Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 33
HIV infection and Its Epidemiology
In the 20 months since the publication of Confronting AIDS, much has
been learned about the clinical history of HIV infection and about the
dimensions of the epidemic. New information has arisen from continuing
clinical observation, surveillance systems, and epidemiological studies. In
this chapter, we focus on some important aspects of the disease and the
epidemic in areas in which new data have either confirmed or altered initial
impressions or in which a deeper understanding of the disease has emerged.
These areas include the causative agent of AIDS, the proportion of seropo-
sitive persons who will develop AIDS, HIV infection as a continuum of
conditions, the modes and efficiencies of HIV transmission, and the preva-
lence and incidence of HIV infection and the dimensions of the epi-
demic in the United States (global epidemiology is discussed in Chapter 71.
HIV: THE ETIOLOGIC AGENT OF AIDS
Early in the epidemic, epidemiological analysis of the pattern of the
spread of AIDS showed it to be reminiscent of that for hepatitis B virus,
an observation that pointed scientists in the right direction in their search
for an etiologic agent. In 1983 and 1984 several researchers identified a
retrovirus that is now understood to be HIV as the cause of AIDS. The
committee believes that the evidence that HIV causes AIDS is scientifically
conclusive.
That a particular organism causes a disease is demonstrated by a
confluence of evidence linking the two: HIV and AIDS have been so
33
OCR for page 34
34 CONFRONTING AIDS: UPDATE l 988
linked in time, place, and population group. For example, in San
Francisco, the examination of frozen blood from a cohort of homosexual
men showed the appearance of antibodies to HIV as early as 1978. At that
time, the prevalence of HIV infection was probably less than 5 percent in
the population of male homosexuals in San Francisco. The first cases of
AIDS in homosexual men in San Francisco were detected in 1981 (CDC,
19811. This association between the cumulative incidence of HIV infec-
tion and of AIDS cases is the epidemiological pattern that must exist if
HIV and AIDS are causally associated: the virus must be newly intro-
duced into the population, it must become widely prevalent, and its
dissemination must precede the incidence of AIDS (Winkelstein, 19881.
The conjunction heralded by the joint appearance of HIV and AIDS has
been confirmed by their continued association. HIV seropositivity rates
in defined subpopulations of homosexual men in San Francisco and New
York City and in IV drug abusers in New York City are associated with
later cases of AIDS in the same groups (Curran et al., 19881. In San
Francisco, these subpopulations can be further broken down by neigh-
borhood of residence, in which the association between HIV seropositiv-
ity and AIDS is also high (Winkelstein et al., 1987b). Conversely, AIDS
is unknown in populations that are free of HIV antibodies.
The virus has been isolated from persons with AIDS; as assay tech-
niques have improved, close to 100 percent of affected individuals can be
found to harbor the virus (Booth, 19881. The virus is not found in persons
who are not at risk for infection. These points are supported by epidemi-
ological data from the ongoing San Francisco Men's Health Study, which
began in 1984. Among 374 homosexual men who remained uninfected
with HIV during the first 30 months of follow-up, no cases of AIDS
occurred. Among 36 homosexual men who became infected with HIV
during this period, 3 cases of AIDS (8 percent) occurred. Among 399
study subjects who were infected with HIV when they entered the study,
52 (13 percent) developed AIDS. None of the heterosexual men in the
study acquired HIV infection, and none developed AIDS. The probability
that this distribution might have occurred by chance is less than one in a
million (Winkelstein, 1988~.
Perhaps the clearest evidence linking HIV to AIDS is to be found in the
tragic results of blood transfusions in the United States and around the
world. The transmission of HIV in contaminated blood and blood
products has been clearly linked to AIDS (Curran et al., 1984~; in the
United States, over 1,500 reported cases of AIDS are associated with
blood transfusions. Since routine screening of the blood supply for
antibodies to HIV began in 1985, HIV transmission by this route has
practically disappeared. Nevertheless, 13 recipients from 7 donors who
initially tested negative for HIV antibodies are known to have acquired
OCR for page 35
HIV INFECTION AND ITS EPIDEMIOLOGY 35
HIV infection between March 1985 and October 1987 (Ward et al., 19881.
The 7 donors, who were tested at the time of donation, probably had
negative test results because testing occurred soon after infection and
before the development of detectable antibodies. On later retesting,
however, all 7 donors were found to have detectable HIV antibodies in
their blood. Of the 13 recipients, 1 developed AIDS, and 3 developed
HIV-related illnesses. Of the 3 developing illness, 1 was an infant twin
who received transfusions shortly after birth; her fraternal twin, who
received no transfusions, remained healthy. Thus, 13 people with no
other risk factors became infected, and 4 of them developed the illness
after receiving transfusions from donors who were initially thought to be
free of infection. After careful investigation, the donors were found, in
fact, to have HIV infection.
The causal role of HIV in AIDS is also supported by the high risk (30
to 50 percent) of perinatal HIV transmission from an infected mother to
her infant (CDC, 1987b) and the subsequent diagnosis of AIDS in the
infected infants.
The pathogenesis of HIV infection how the organism causes dis-
ease is still incompletely understood. Several mechanisms have been
proposed for the profound immunodeficiency that results from HIV
infection, including the aggregation of uninfected and infected T lympho-
cytes into multinucleated syncytia that subsequently die, the infection of
stem cells, and the inhibition of lymphocyte functions by viral products.
A complete understanding of a disease's pathogenesis, however, is not a
prerequisite to knowing its etiology.
PROPORTION OF INFECTED INDIVIDUALS WHO
WILL DEVELOP AIDS
As epidemiological cohorts of HIV-infected individuals are observed
over time, a larger and larger proportion of seropositive persons has been
seen to develop AIDS. The available data suggest that the great majority
of HIV-infected persons will eventually progress to AIDS in the absence
of effective therapy to slow or halt the infection's progression.
The cohort of individuals that has been studied longest in relation to
AIDS is a group of gay men in San Francisco who were enrolled in a study
of hepatitis B virus vaccine in the late 1970s. As part of the study, blood
samples were collected, from which serum was saved and frozen.
Because this group of men was later found to be at high risk for AIDS,
samples of the frozen serum were analyzed for HIV infection, and
infected individuals have been followed for clinical and laboratory evi-
dence of AIDS. Almost no cases of AIDS occurred during the first 2 years
after infection was discovered. After 8~/2 years, more than 40 percent of
OCR for page 36
36 CONFRONTING AIDS: UPDATE 1988
the infected cohort has developed AIDS; a similar proportion has
developed symptoms of HIV infection and is expected to progress to
AIDS. Statistical modeling of the incidence of AIDS in this cohort
predicts the possibility that 100 percent will develop AIDS within 13 years
after initial infection (G. W. Rutherford, San Francisco Department of
Public Health, personal communication, 1988~.
The analysis of another cohort of 288 seropositive homosexual men in
San Francisco who were seropositive when the study began shows that 22
percent have developed AIDS after 3 years of observation. Another 19
percent have clinical symptoms of infection, and an additional 24 percent
demonstrate laboratory evidence of immunologic compromise. Projec-
tions for this cohort are that 50 percent of the men will develop AIDS
within 6 years of observation (or probably 9 years of infection) and that
many more will develop the disease in subsequent years (Moss et al.,
1988).
Data from individuals infected with HIV through blood transfusions
and data from persons with hemophilia suggest that the rate of progres-
sion from HIV infection to AIDS increases with age. The exception to this
pattern is newborns, who have the highest progression rate of all age
groups (Eyster et al., 1987; Medley et al., 19871. The progression rate in
adults with hemophilia appears to be similar to that in male homosexuals
(Goedert and Blattner, in press).
THE SPECTRUM OF HIV INFECTION
In grappling with a new disease, especially one that quickly assumes
epidemic proportions, terminology and definitions become vital for clin-
ical management of patients, data gathering and research, and decisions
about coverage and reimbursement. In 1982 CDC developed a definition
of AIDS for surveillance purposes that relied on the presence of oppor-
tunistic infections and malignancies; in August 1987 the definition was
revised to incorporate two other syndromes indicative of AIDS: dementia
and wasting syndrome (see Appendix B). Yet fairly early in the epidemic,
it became apparent that many infected individuals who suffered from
clinical symptoms and laboratory abnormalities signaling the presence of
HIV infection did not meet the CDC criteria for the disease. For example,
persistent generalized Iymphadenopathy (PGL) was thought to be asso-
ciated with an increased risk of developing AIDS, especially when
combined with oral candidiasis and certain laboratory abnormalities.
Another group of patients displayed other chronic symptoms of AIDE
fever, weight loss, night sweats, chronic diarrhea, and fatigue and a high
proportion of this group also exhibited laboratory abnormalities. Even so,
these patients did not fit what had become the standard definition of the
OCR for page 37
HIV INFECTION AND ITS EPIDEMIOLOGY 37
disease, although some of them seemed to develop AIDS at a rapid
pace. They were described as having AIDS-related complex (ARC), and
the ARC clinical syndrome was eventually incorporated in a CDC
definition (although it was never used as a basis for case reporting).
Clinicians noted, however, that even this definition failed to include
some patients who appeared to be at high risk for progressing to AIDS.
A third, more broadly defined syndrome was termed the AIDS-related
condition.
Today, with a better understanding of the natural history of HIV
infection and with more precise laboratory assessments of disease pro-
gression, the committee believes that the term ARC is no longer useful,
either from a clinical or a public health perspective, and that HIV infection
itself should be considered a disease. It is more accurate to describe HIV
infection as a continuum of conditions, ranging from the acute, transient,
mononucleosis-like syndrome associated with seroconversion, to asymp-
tomatic HIV infection, to symptomatic HIV infection, and, finally, to
AIDS, a spectrum that encompasses a great variety of clinical symptom-
atology. The terms ARC and PGL do not have the precise prognostic
implications they were once thought to have. For instance, it is now
known that the presence of persistent, generalized lymphadenopathy in
and of itself does not imply a worse prognosis than HIV seropositivity.
For clinical (treatment or research) purposes, a patient can be more
accurately described by a combination of a description of symptoms and
laboratory evidence of immune dysfunction rather than by terms such as
ARC or PGL.
Experience with cohorts of infected individuals indicates that a major-
ity of HIV-infected individuals shows some evidence of progressive
immunodeficiency and is likely to develop AIDS in the absence of
effective therapy. AIDS, a dramatic and devastating syndrome, caught
the attention of physicians and public health officials earlier than the
milder manifestations of HIV infection, but it is now clear that AIDS is
end-stage HIV infection. Like many other progressive disease processes,
both infectious and noninfectious, HIV has an asymptomatic period that
varies in length.
Viewing HIV infection as a disease is important because it may
eventually be amenable to treatment. The drug zidovudine (i.e., AZT) has
been shown to prolong the life of AIDS patients; it and other drugs are
currently being tested to determine whether they also halt or slow disease
progression in infected asymptomatic individuals. If an effective therapy
is found, HIV infection will need to be treated early, just as diseases such
as gonorrhea are often diagnosed and treated in asymptomatic infected
patients. Even though no treatment is available, diagnosing HIV infection
is still important now so that opportunistic infections and malignancies
OCR for page 38
38 CONFRONTING AIDS: UPDATE 1988
ACUTE ASYMPTOMATIC
STAGE SEROPOSITIVE TRANSITION LATE
4 ' it,
-
-
VIRUS
ANTIBODY
-
AIDS
\ /\
VIRUS
,_
-
_ ~
/CD4 CELLS /
WEEKS
YEARS
FIGURE 1 The course of disease from HIV infection to AIDS. Source: Courtesy
of David Baltimore, Whitehead Institute for Biomedical Research, Cambridge,
Massachusetts.
can be recognized as early as possible. Many treatments for these
complications are more effective and less toxic when initiated early.
Considering HIV infection a disease is important to other aspects of the
AIDS crisis. From a public health perspective, the population of most
interest is the group infected with the virus, because these persons are
capable of infecting others. In addition, as discussed in Chapter 5,
medical care coverage should be based on symptoms associated with HIV
infection rather than on arbitrary definitions of when "disease" begins. A
terminology that reflects the progression of the disease from the initial,
acute stage of infection to asymptomatic HIV infection and finally to
symptomatic HIV infection and AIDS (Figure 1) would be useful for
clinical treatment and for society's management of the disease. CDC has
developed a classification system (see Appendix B) that might form the
basis for such a terminology.
MODES AND EFFICIENCIES OF HIV TRANSMISSION
Epidemiological data continue to support the observation that HIV
transmission is limited to sexual contact, the sharing of contaminated
OCR for page 39
HIV INFECTION AND ITS EPIDEMIOLOGY 39
needles and syringes, exposure to infected blood or blood products,
transplantation of infected organs or tissue, and transmission from mother
to child either across the placenta or during delivery. A recent follow-up
investigation of more than 1,100 AIDS cases that were initially reported to
CDC as having no identified risk factors has shown that transmission in
these individuals was also limited to the recognized routes (Castro et al.,
19881. Finally, additional data from studies of health care workers (CDC,
1988d), nonsexual household contacts (Friedland and Klein, 1987), and
insect bites (CDC, 1986) all support the conclusion that HIV is not
transmitted by casual contact or insect bites. A change in HIV transmis-
sion modes would be biologically unprecedented in a virus. There is no
evidence that HIV is capable of such a change.
Heterosexual Transmission
It has been clearly documented that HIV infection can be transmitted
from men to women and from women to men through vaginal and anal
intercourse (Fischl et al., 1987; Goedert et al., 1987; Padian et al., 1987a;
Peterman et al., 19884. So far, however, the heterosexual spread of the
virus in the United States has been confined mainly to persons whose
sexual partners acquired HIV by other means for example, by sharing
contaminated needles and syringes or from blood transfusions.
Evidence to date shows that the spread of infection among heterosex-
uals has been rather slow in instances in which neither partner can be
classified in a known risk category (CDC, 1988b). In nine seroprevalence
surveys of heterosexual men and women attending sexually transmitted
disease (STD) clinics in six cities, the prevalence of HIV infection ranged
from O to 2.6 percent (CDC, 1987b). STD clinics treat individuals in the
community who, because of their sexual behavior, are most likely to be
infected with HIV. In studies conducted in clinics in which data were
collected during personal interviews and not through self-administered
questionnaires, and in which seropositive individuals were reinterviewed
to obtain better information about their risk status, the prevalence of HIV
infection ranged from O to 1.2 percent among persons with no known risk
factors. The results obtained from large-scale studies of over 36 million
blood donations and 1.5 million military personnel (in which there are
indications of the self-exclusion of persons at high risk) show that the
overall prevalence of HIV has been less than 1 percent in these popula-
tions for the period 1985 to 1987. This low prevalence among heterosex-
uals (compared to the 20 to 50 percent prevalence among male homosex-
uals) appears to indicate that the virus is not spreading rapidly in
populations that are considered to be primarily low-risk groups.
To become complacent in the face of this apparent trend would be a
mistake, however. Heterosexual transmission of the virus is an estab-
OCR for page 40
40 CONFRONTING AIDS: UPDATE 1988
fished fact; although the numbers are small, cases acquired through
heterosexual transmission are the fastest growing group of AIDS cases in
the United States. Indeed, in parts of Africa, heterosexual transmission of
HIV is great enough to sustain AIDS in an epidemic status (see Chapter
7~. It is useful to review the African experience with AIDS and attempt to
pinpoint conditions that may augur changes in the patterns of disease
spread in the United States.
It is believed that, in Africa, HIV infection appeared in great numbers
first in the heterosexual community and that prostitution has played a
major role in its spread. Prostitution is not uncommon in some urban
areas in central and east Africa, and the prevalence of HIV infection is
quite high (25 to 88 percent) among the prostitutes tested in some of those
areas (Kreiss et al., 1986; Plot et al., 1988~. Case-control studies have also
shown that sexual activity with female prostitutes is more common among
men with AIDS than among controls; African patients with AIDS also
report contact with more heterosexual partners than do controls (Quinn
et al., 19861. On the other hand, homosexuality and IV drug abuse do
not play a major role in HIV transmission in Africa (Plot et al., 1988~.
In addition, STDs, in particular, genital ulcers, are fairly prevalent in
some sexually active populations in Africa and are associated with an
increased risk of infection, perhaps by providing a more direct portal of
entry into the bloodstream. The contamination of the African blood
supply and frequent exposure to unsterilized needles and syringes in
both medical settings and ritual practices may also be important factors
in the spread of AIDS among the African heterosexual population.
Furthermore, African heterosexual adults show chronically activated
immune systems more frequently than American heterosexual men,
which may be a factor that increases their susceptibility to HIV
infection (Quinn et al., 19871.
The pattern of disease spread in the United States has been much
different. Here, the epidemic began in a few cities and within a closed
community male homosexuals in which high-risk behaviors were prac-
ticed (multiple partners and receptive anal intercourse). These behaviors
enhanced the rapid spread of HIV infection within that community, which
also had high STD rates, another factor that may have increased the risk
for HIV infection. The observation that the spread of HIV infection into
the heterosexual community appears to be much slower suggests that one
or more of the following may be true: (1) there has been relatively little
sexual contact between this pool of infected men and heterosexuals; (2)
heterosexuals probably change partners less frequently than homosexual
men; and (3) vaginal intercourse may not spread the virus as easily as anal
intercourse. Consequently, HIV infection in the heterosexual population
in the United States has been somewhat contained.
OCR for page 41
HIV INFECTION AND ITS EPIDEMIOLOGY 41
Similarly to the appearance of disease among homosexual men, HIV
infection also ~ame~onounced in communities of IV drug abusers who
practiced high-risk behaviors—in this instance, frequent drug injections
and the sharing of contaminated drug injection equipment. These behav-
iors are the functional equivalents of frequent receptive anal intercourse
and multiple sexual partners among homosexual men. Here also, the
spread of infection was rapid but contained (Robertson et al., 1986; Des
Jarlais et al., 1988~. The potential for the spread of infection beyond the
IV drug-abusing population is discussed below.
- Will HIV infection reach epidemic proportions in the `'general" het-
erosexual population in the United States, and are the conditions neces-
sary for such an epidemic already in place? Sustaining the spread of the
disease requires a "chain of transmission" from individuals practicing
high-risk behaviors to their partners and from them to individuals with no
known risks. This chain of transmission would have to include sufficient
numbers of infected women interacting with men who would not other-
wise be at high risk. Such a reservoir of infected women might be created
in several ways: one mechanism is bisexuality; another probably more
significant avenue is IV drug abuse (Guinan and Hardy, 1987; Moss et al.,
1987~. Of all IV drug abusers, 90 percent are heterosexuals, and 30
percent are women. Moreover, between 30 and 50 percent of female IV
drug abusers have engaged in prostitution. Thus, there exists the possi-
bility that a pool of infected prostitutes might be created (whose source of
infection is the sharing of contaminated needles and syringes). HIV
infection could then enter the heterosexual community from male cus-
tomers of female prostitutes.
To date, most of the cases of AIDS among heterosexuals have resulted
from IV drug abuse, and the number of infected addicts is growing.
Moreover, seroprevalence among heterosexuals with no known risk
factors is higher in areas of the country in which seroprevalence among
IV drug abusers is high. This correspondence means that IV drug abusers
play a pivotal role in the spread of HIV to adults through heterosexual
transmission (and to infants through perinatal transmission).
For 1987, a 30 percent increase in syphilis was reported in the United
States (CDC, 1988c), primarily among heterosexuals. Higher rates were
reported for blacks and Hispanics than for whites. In addition, the areas
reporting the largest absolute increases in syphilis cases (i.e., Florida,
New York City, and California) were also areas that have high rates of
HIV infection. The increases in syphilis cases suggest that behavior that
increases the probability of HIV infection among heterosexuals is not
being effectively curtailed.
In sum, the evidence to date is that heterosexual HIV transmission
occurs from men to women and from women to men through vaginal and
OCR for page 42
42 CONFRONTING AIDS: UPDATE 1988
anal intercourse. The virus is capable of spreading among heterosexuals,
but so far the prevalence of infection in the heterosexual population with
no known risks for infection is low. Yet the extent of future heterosexual
spread is uncertain. A "window of opportunity" apparently exists for
preventing the further spread of infection to the heterosexual population.
Efficiencies of Transmission
The modes of HIV transmission are well documented. What is not as
clear is how easily or how "efficiently" HIV is transmitted by a particular
route if an individual is exposed. Specially designed epidemiological
studies provide information that helps to estimate the probability of HIV
transmission by the various known routes.
Blood Transfusions. The efficiency of this transmission route can be
estimated using studies of the recipients of blood from donors who were
subsequently found to have AIDS or HIV antibodies. Between 66 and 100
percent of blood transfusion recipients became infected if donors either
tested positive for antibodies to HIV or later became antibody positive or
developed AIDS (Ward et al., 1987~. Furthermore, recipients were more
likely to become infected if the transfusion occurred close to the time the
donor developed symptoms. All recipients of blood transfusions became
infected if the donors developed AIDS within 23 months of the donation
(Ward et al., 1987~. Thus, the large dose of the virus a transfusion
represents, coupled with this particular route, appears to be quite efficient
as a transmission path.
Perinatal Transmission. Risk of transmission can also be estimated
from studies that evaluate the risk that an HIV-infected pregnant
woman will deliver an infected infant. The results from such studies
suggest that the probability of HIV transmission from mother to infant
ranges from 30 to 50 percent (CDC, 1987b). Some studies suggest that
the risk of transmission is higher for infants born to mothers who have
symptoms of HIV infection during pregnancy or who show evidence of
immunosuppression (Mok et al., 1987; Nzilambi et al., 1987; Plot et al.
1988).
IV Drug Abuse. Information on HIV transmission through the sharing
of contaminated needles and syringes is hard to gather because of the
illicit nature of IV drug abuse. However, several studies have shown that
once HIV is introduced into a community, its spread is rapid among IV
drug abusers and a majority of them soon becomes infected (Novick et
al., 1986; Robertson et al., 1986; Des Jarlais et al., 1988~. In New York
City, where there are large numbers of infected IV drug abusers, the
patterns of needle-sharing behavior include the practice of renting used
needles and other drug paraphernalia in "shooting galleries" in which IV
OCR for page 43
HIV INFECTION AND ITS EPIDEMIOLOGY 43
drug abusers gather (Friedland and Klein, 19871. Studies of IV drug
abusers have shown an association between HIV seropositivity and both
the frequency of drug injections and the sharing of drug injection
equipment (Chaisson et al., 1987b; Marmor et al., 19871.
Homosexual Transmission. The risk of HIV transmission from recep-
tive anal intercourse between homosexual men has been estimated,
although partner tracing among homosexuals can be difficult in situations
in which there have been multiple sexual partners (Grant et al., 1987~.
Cohort and case-control studies of homosexual men (Darrow et al., 1987;
Kingsley et al., 1987; Moss et al., 1987; Winkelstein et al., 1987) show that
the risk of HIV infection is greatest for persons who engage in receptive
anal intercourse. The risk of infection is less for partners who engage in
insertive anal intercourse, and the risk appears even lower for oral
receptive intercourse.
Heterosexual Transmission. Estimates of the risk of heterosexual
transmission have been derived from studies of the sex partners of
infected persons. In this study design, an index case (the infected person)
is identified, and the antibody status of his or her sexual partner is
determined at entry and observed over time. In several studies of female
partners of IV drug abusers, the risk of infection was reported to be about
50 percent (Curran et al., 1988~. Studies of the male sex partners of female
IV drug abusers found similarly large risks of infection, although the
numbers of male partners tested were small. In these studies, HIV
transmission by the sharing of contaminated needles and syringes cannot
be ruled out.
The risk of transmission is lower for female partners of hemophiliacs
and bisexual men and for partners of transfusion-infected persons than it
is for male or female partners of IV drug abusers (Padian, 1987; Padian et
al., 1987a; Curran et al., 1988; De Gruttola and Mayer, 1988; Johnson,
19881. In studies of the wives or female partners of hemophiliacs, the risk
of infection was about 10 percent. Studies of female partners of bisexual
men reported a risk of transmission of around 25 percent. Risks of
similar magnitude have been found in studies of the spouses of
transfusion-infected persons. In a recent study, of the 55 wives who had
sexual contact with their infected partners, 10 (18 percent) became
seropositive (Peterman et al., 1988~. In this study, the risk of infection
was not related to the number of sexual contacts a woman had with her
infected spouse; in fact, seropositive wives reported fewer sexual
contacts and were somewhat older than seronegative wives. This result
suggests that, in addition to behavioral factors, biological factors
probably play a role in determining how easily HIV is transmitted.
There may be differences in transmissibility as a result of changes in the
infectiousness of the infected individual over time. Thus, heterosexual
OCR for page 46
46 CONFRONTING AIDS: UPDATEl988
PREVALENCE AND INCIDENCE OF HIV INFECTION
IN THE UNITED STATES
The importance of accurate descriptions of the prevalence and inci-
dence of HIV infection, both at present and for the future, cannot be
overstated. Defined cases of AIDS are only the clinical end stage of the
devastating effects produced by HIV infection. The description of HIV
infection by demographic characteristics and other distinguishing features
helps determine which groups to target for intervention strategies to
prevent the further spread of infection.
HIV Prevalence in Groups at Recognized Risk
In November 1987, CDC summarized current knowledge of the prev-
alence and incidence of HIV infection for various segments of the United
States population according to age, sex, race or ethnic group, and
geographic area (CDC, 1987b). The report reviewed data obtained from
several sources (including federal agencies, health departments, and
medical centers) on the prevalence of HIV infection as measured by the
presence of HIV antibodies in the blood (i.e., seroprevalence).
The observed prevalence of HIV infection is highest in those risk
groups that account for the majority of AIDS cases reported to CDC.
Still, caution is needed in interpreting prevalence data. For example, the
prevalence of HIV infection may be seen to vary in STD clinics in
different geographic areas because the background prevalence in any two
communities may be different. Other problems in comparing data arise
from differences in questionnaire design, the inclusion or exclusion of
symptomatic individuals in reports of seroprevalence, and differences in
the demographic characteristics of the individuals being tested. Further,
reported prevalence may be higher or lower than the true prevalence for
a given group depending on who "walked in the door" (i.e., most of these
surveys are based on self-selected samples).
Estimates of the prevalence of HIV infection in homosexual and bisexual
men based on data from 23 cities range from 10 to 70 percent, with most
estimates falling between 20 and 50 percent (CDC, 1987b). Prevalence is
highest in cohorts of homosexual men in San Francisco. Yet the data
probably overestimate the true prevalence of HIV infection in this group
because most of the respondents to these surveys were persons who were
either seeking medical attention for STDs or who were concerned that their
past or present sexual behavior had placed them at risk (Curran et al., 19881.
The populations of IV drug abusers appear to be less mobile than the
population of homosexual men, as larger differences in HIV prevalence are
reported by geographic area. Surveys consistently show very high preva-
OCR for page 47
HIV INFECTION AND ITS EPIDEMIOLOGY 47
fence (50 to 60 percent) in major East Coast cities with geographic or close
cultural connections to New York City and northern New Jersey; prevalence
is much lower (less than 5 percent) in other areas of the country (CDC,
1987b). Most of the surveys measuring prevalence in IV drug abusers are
conducted at facilities for chronic heroin abuse treatment. It is thought that
only 10 to 20 percent of the estimated 1.2 million drug abusers in the United
States are currently in treatment and that those not in treatment may be
habitual users whose risk for HIV infection is even greater (CDC, 1987b).
The prevalence of HIV infection for persons with hemophilia ranges from
15 percent to more than 90 percent, depending on the type and severity of
hemophilia and, in turn, the amount of clotting factor received (CDC, 1987b).
Persons with severe hemophilia A have the highest prevalence (approxi-
mately 70 percent), whereas persons with hemophilia B or mild hemophilia
A have a somewhat lower prevalence (approximately 35 percent). Within
these clinical categories, however, prevalence is uniform throughout the
country, reflecting the distribution of clotting factor concentrate received
before 1985. Only hemophiliacs who seek treatment are tested; conse-
quently, the prevalence reported here may be an overestimate of the true
prevalence for hemophiliacs as a group (CDC, 1987b).
The prevalence of HIV in female prostitutes in the United States varies
from 0 percent to more than 50 percent. Seropositivity is higher in black
and Hispanic prostitutes than in white prostitutes. The differences in
prevalence appear to be related to the extent of IV drug abuse in the
groups tested and the background HIV prevalence in IV drug abusers in
the area (CDC, 1987b).
In studies of seroprevalence conducted among persons who are hexers
sexual sex partners of HIV-infected persons but who have no other identi-
fiable risk factors for HIV infection, prevalence ranged from less than 10
percent to 60 percent (CDC, 1987b). As noted earlier in this chapter, surveys
in STD clinics of heterosexual men and women who do not belong to any risk
group and who do not have partners in any risk group report prevalences
ranging from 0 percent to 2.6 percent, depending on the population studied
and the method of data collection. Seroprevalence is higher among hetero-
sexuals in areas in which seroprevalence in IV drug abusers is high.
However, such studies may overrepresent the true prevalence of HIV
among heterosexuals because people surveyed in STD clinics may be more
sexually active than the "general" heterosexual population.
HIV Prevalence Among Selected Segments of the
General Population
The prevalence of HIV infection in the population at large has been
estimated primarily from studies of various special populations: blood
OCR for page 48
48 CONFRONTING AIDS: UPDATE 1988
donors, civilian applicants to the military, Job Corps entrants, sentinel
hospital patients, and newborn infants (whose antibody status at birth
reflects the presence or absence of antibodies in their mothers) (CDC,
1987b). More than 36 million blood or plasma donations in the United
States have been tested for HIV antibodies since 1985. HIV prevalence
among first-time donors for the period 1985 to 1987 was 0.04 percent.
Prevalence was much higher for men than for women and higher for
blacks and Hispanics than for whites. Since October 1985, blood samples
from over 1.5 million applicants for military service have also been tested
for HIV antibodies. The prevalence of HIV infection increases with age
for applicants between the late teens and late twenties. Prevalence by
birth year cohorts also increased from the first screening period
(1985-1986) to the second (1986-1987~. As with blood donors, seroposi-
tivity was higher for men than for women and higher for blacks and
Hispanics than for whites. The overall prevalence (for October 1985 to
September 1987), adjusted for the age, sex, and racial and ethnic
composition of the U.S. adult population aged 17 to 59 years, was 0.14
percent. Since March 1987, HIV antibody screening has been conducted
for new members of the Job Corps who participate in residential training
programs. This program recruits rural and inner-city disadvantaged
youths aged 16 to 21. Provisional data from the first 25,000 entrants
showed a seroprevalence of 0.33 percent. The prevalence of infection in
the nation as a whole is probably higher than what has been observed in
blood donors, applicants to the military, and Job Corps entrants, as
persons at highest risk for infection are probably underrepresented.
To avoid the self-selection bias associated with volunteer programs,
anonymous HIV antibody testing has also recently begun on selected
hospital patients (excluding AIDS cases and other conditions related to
HIV infection) at sentinel hospitals. Based on the first 8,668 test results,
the age- and sex-adjusted prevalence of infection was 0.32 percent. This
sample represents hospitalized patients who are at low risk for infection.
In addition, the hospitals selected to participate in the program may
service specialized segments of the community; therefore, the data
collected are not representative of all hospitalized patients.
Several states have begun programs to assess the prevalence of HIV
infection in women of childbearing age by testing for HIV antibodies in
their newborns. Maternal antibodies against HIV cross the placenta and
are therefore present in the baby's blood. A baby with antibodies to HIV
may or may not itself be infected; however, the presence of antibodies in
the baby's blood always indicates that the mother is infected. Neonatal
blood specimens are routinely collected in hospitals to test for metabolic
disorders; the test for HIV antibodies has been added to this program. A
recent study has reported that 1 of every 476 women (0.2 percent) giving
OCR for page 49
HIV INFECTION AND ITS EPIDEMIOLOGY 49
birth in Massachusetts was antibody positive during the period December
1986 to June 1987. The prevalence of HIV infection differed according to
the type and location of the maternity hospitals. Prevalence was highest
in inner-city hospitals (0.8 percent), lower in mixed urban and suburban
hospitals (0.25 percent), and lowest in suburban and rural hospitals (0.09
percent) (Hoff et al., 1988~. In New York, the prevalence of HIV infection
among women delivering babies in hospitals in the five New York City
boroughs between November 1987 and February 1988 was 1.45 percent;
the prevalence of HIV infection among women delivering babies in
hospitals outside the metropolitan area was 0.18 percent (Novick et al.,
1988).
Incidence of New Infections
Data on the incidence (the number of new infections over time) of HIV
infection are more difficult to obtain than prevalence data, but they are
crucial for longer term projections of the course of the epidemic.
Evidence from eight cohort studies of gay men suggest a lower HIV
incidence rate in that population for 1985-1987 than in the earlier part of
the decade (CDC, 1987b). This observed decline in the incidence of
infection may be attributed to several factors, but it is consistent with
reports of a decline in other sexually transmitted diseases in this group
(CDC, 1988c) as well as changes in sexual behavior (Winkelstein et al.,
1987a). Serologic screening of blood and plasma donors and heat treat-
ment of factor concentrate, as well as efforts to exclude donors at high
risk, have also reduced the rate of new infection among transfusion
recipients and hemophiliacs since 1985. In contrast, HIV incidence
appears to be increasing in IV drug abusers in New York City and San
Francisco (Chaisson et al., 1987a; Des Jarlais et al., 1987; Schoenbaum et
al., 1987~. These data suggest that the epidemic of HIV infection in the
United States may be viewed as a series of overlapping smaller epidem-
ics, each with its own dynamics and time course (Curran et al., 1988~.
National Estimates of HIV Infection
In 1986, CDC estimated the size of various segments of the population
that were known to be infected (i.e., male homosexuals, IV drug abusers,
hemophiliacs, heterosexuals with no known risks), as well as the preva-
lence of HIV infection for each of these groups. It then calculated from
these estimates that 1 to 1.5 million people in the United States were
currently infected with HIV. In November 1987, CDC reviewed these
estimates and modified them slightly based on new information about the
size of the various populations and new seroprevalence data for these
OCR for page 50
50 CONFRONTING AIDS: UPDATE 1988
groups. In retrospect, the 1986 estimates made by CDC appear to have
been too high. CDC now estimates that between 945,000 and 1.4 million
Americans currently are infected with HIV. The major limitation of both
the original and the revised estimates is the unknown size of the
homosexual population that engages in at-risk behaviors (CDC, 1987b).
CDC will continue to update national estimates of the prevalence of HIV
infection as more information is gathered. Other groups and investigators
have also estimated the prevalence of HIV infection in the United States;
these estimates have been both higher and lower than those made by
CDC, ranging from 400,000 to 2.2 million for the end of 1987 (De Gruttola
and Lagakos, 1987; Harris, 19874. Such estimates provide an overall
picture of the magnitude of the epidemic; however, seroprevalence and
incidence data on specific groups at risk are more important because they
offer the necessary information to target prevention strategies and eval-
uate their effectiveness in curbing the epidemic.
The Program of HIV Surveys and Studies
CDC has responded to the urgent need to monitor the spread of HIV
infection by instituting a series of seroprevalence studies and surveillance
systems (Dondero et al., 19881. In approximately 30 metropolitan areas in
the United States, blood samples will be routinely collected from persons
treated at STD clinics, drug abuse treatment centers, family planning and
women's health clinics, and tuberculosis clinics, as well as from selected
hospital admissions and newborns. These studies will provide local
officials with information on HIV prevalence so that interventions can be
designed to control HIV infection in specific settings. The surveys of
newborns will provide some of the most valuable information because
sample selection is unbiased; the entire population of childbearing moth-
ers is included. As noted earlier, testing for HIV antibodies, which will
occur in approximately 30 states, will be added to already existing
programs that routinely test newborns for metabolic disorders. These
surveys will, therefore, be population based and, by providing informa-
tion on the antibody status of newborns, will reflect the prevalence of
infection in mothers delivering in these hospitals.
In addition to these activities, studies of HIV infection will continue in
civilian applicants to the military services, active duty military personnel,
blood donors, and Job Corps entrants. Surveys of HIV prevalence will
also be conducted in other populations of special interest such as patients
from emergency rooms, patients using other hospital services, students
on college campuses, and prisoners. The National Center for Health
Statistics (NCHS) will also conduct a study to determine the feasibility of
a nationwide household seroprevalence survey. In addition, NCHS also
OCR for page 51
HIV INFECTION AND ITS EPIDEMIOLOGY 51
plans to include anonymous HIV antibody testing of an estimated 17,000
blood specimens collected from adults over a 6-year period as part of the
National Health and Nutrition Examination Survey.
It is important to note that some of these surveys will be "blinded"
(i.e., HIV antibody testing will be done on blood specimens collected for
other purposes with personal information on the individual permanently
removed) to avoid the uninterpretable impact of self-selection bias. Other
surveys, however, will be nonblinded. In these settings, volunteer par-
ticipants will be interviewed to evaluate risk factors for HIV transmis-
sion.
AIDS CASES IN THE UNITED STATES
In October 1986, when Confronting AIDS was published, approxi-
mately 24,500 cases of AIDS had been reported to CDC. As of May 1988,
62,200 cases of AIDS had been reported since June 1981, and 35,051 of
these had ended in death (CDC, 1988a). An additional 10 to 20 percent of
cases are believed to have been missed by the surveillance system. The
number of cases reported each year continues to increase, although the
rate of increase is less steep than it was earlier in the decade. Cases have
been reported from all 50 states and the District of Columbia.
Since the publication of Confronting AIDS, the distribution of cases by
risk group as well as by sex, race, age, and geographic area has not
changed substantially: 63 percent of cases are homosexual or bisexual
men not known to have abused IV drugs, 19 percent are heterosexual IV
drug abusers, 7 percent are both male homosexuals and IV drug abusers,
1 percent are patients with hemophilia and related disorders, 4 percent are
persons who acquired the disease through heterosexual contact, 3 percent
are recipients of blood transfusions, and 3 percent are cases in which risk
information is undetermined because it is incomplete (patients have died,
refused to be interviewed, or have been lost to follow-up) or the patients
are still under investigation. This 3 percent also includes men reporting
contact with a prostitute and patients with no identifiable risk factor. Of
the 981 cases of AIDS among children that had been reported to CDC by
May 1988, 77 percent are offspring of a parent with AIDS or at high risk
for AIDS. Of the remaining pediatric cases, 6 percent are children with
hemophilia, 14 percent are transfusion recipients, and 4 percent are
children for whom risk information cannot be determined.
Over the past 2 years, the largest increases in new cases have been
observed in two groups: heterosexual partners of HIV-infected individu-
als and children whose mothers abuse IV drugs or are sexual partners of
men at high risk. There is an overrepresentation of blacks and Hispanics
in both of these groups. The only group showing a steady decline in AIDS
OCR for page 52
52 CONFRONTING AIDS: UPDATE 1988
incidence over the past 2 years has been children with transfusion-
associated AIDS. This decline is attributed to the screening of blood and
blood products that began in early 1985 and to the rather short incubation
period of 12 months or less observed for children with transfusion-
associated AIDS. It is now thought that more than 80 percent of HIV
infection in children can be directly linked to IV drug abuse in the mother
or father.
THE DEMOGRAPHIC IMPACT OF AIDS
AIDS has already begun to alter the demographic characteristics of
New York City and San Francisco. A disease that was virtually unknown
to Americans 8 years ago, AIDS is now the leading cause of death in New
York City among men aged 25 to 44 and women aged 25 to 34. In 1986,
mortality from AIDS was the eighth leading cause of years of potential life
lost before the age of 65 in the United States (CDC, 1988b). Recent data
from New York City indicate that 1 of every 66 infants born between
November 1987 and February 1988 tested positive for HIV antibodies,
reflecting the prevalence of HIV infection in women of childbearing age in
that city (Novick et al., 1988~. In San Francisco, approximately 50
percent of the male homosexual population is infected with the virus,
suggesting the possible future devastation of a large component of the
city's population. In 1986, New York City and San Francisco accounted
for approximately 40 percent of all AIDS cases; by 1991 these two cities
will account for less than 20 percent of cases nationwide (Morgan and
Curran, 1986), suggesting that other metropolitan areas will soon face
major economic and demographic losses.
AIDS cases occur in higher proportions in black and Hispanic popula-
tions than in white populations (on the West Coast, the proportion is 3
times higher in black and Hispanic than in white populations and 12 times
higher on the East Coast), mainly as a result of higher HIV prevalence in
black and Hispanic IV drug abusers and their sex partners and offspring.
Recent data also suggest that the virus is spreading more rapidly among
blacks and Hispanics at risk than among other population groups,
especially in Northeastern cities, suggesting that the future composition
of AIDS cases will consist primarily of poor, urban minorities.
FUTURE RESEARCH NEEDS
Epidemiological studies are the main source of information on the
prevalence and incidence of HIV infection and AIDS, the modes and
efficiencies of HIV transmission, the proportion of infected individuals
who progress to AIDS, serologic markers of disease progression, and the
OCR for page 53
HIV INFECTION AND ITS EPIDEMIOLOGY 53
distribution of behaviors associated with increased exposure to HIV.
Epidemiological studies have also provided some of the strongest evi-
dence for the association between HIV infection and AIDS. Whether or
not these studies are prevalence or incidence surveys, cohort or case-
control in design, they provide essential data to understand and control
the epidemic.
Although much has been learned about the epidemiology of HIV
infection, more research is needed to address its many unanswered
questions. The committee therefore strongly urges continued epidemiolog-
ical research in support of appropriate prevention and control measures.
CDC must be provided with the necessary funding to ensure that
personnel, space, and technical resources are adequate to the task of
continuing epidemiological research.
REFERENCES
Booth, W. 1988. A rebel without a cause of AIDS. Science 239: 1485-1488.
Castro, K. G., A. R. Lifson, C. R. White, T. J. Bush, M. E. Chamberland, A. M. Lekatsas,
and H. W. Jaffe. 1988. Investigations of AIDS patients with no previously identified risk
factors. J. Am. Med. Assoc. 259:1338-1342.
CDC (Centers for Disease Control). 1981. Kaposi's sarcoma and Pneumocystis pneumonia
among homosexual men—New York City and California. Morbid. Mortal. Wkly. Rep.
30:305-308.
CDC. 1986. Acquired immunodeficiency syndrome (AIDS) in western Palm Beach County,
Florida. Morbid. Mortal. Wkly. Rep. 35:609-612.
CDC. 1987a. Antibody to human immunodeficiency virus in female prostitutes. Morbid.
Mortal. Wkly. Rep. 36:157-161.
CDC. 1987b. Human immunodeficiency virus infection in the United States: A review of
current knowledge. Morbid. Mortal. Wkly. Rep. 36(suppl. 6):1-48.
CDC. 1987c. Revision of the CDC surveillance case definition for acquired immunodefi-
ciency syndrome. Morbid. Mortal. Wkly. Rep. 36(suppl. 1):3S-1SS.
CDC. 1988a. AIDS weekly surveillance report—United States, May 16. Atlanta, Gal: CDC.
CDC. 1988b. Changes in premature mortality United States, 1979-1986. Morbid. Mortal.
Wkly. Rep. 37:47-48.
CDC. 1988c. Continuing increase in infectious syphilis United States. Morbid. Mortal.
Wkly. Rep. 37:35-38.
CDC. 1988d. Update: Acquired immunodeficiency syndrome and human immunodeficiency
virus infection among health-care workers. Morbid. Mortal. Wkly. Rep. 37:229-239.
Chaisson, R. E., D. Osmond, A. R. Moss, H. W. Feldman, and P. Bernacki. 1987a. HIV,
bleach, and needle sharing. Lancet 1:1430.
Chaisson, R. E., A. R. Moss, R. Onishi, D. Osmond, and J. R. Carlson. 1987b. Human
immunodeficiency virus infection in heterosexual intravenous drug users in San Fran-
cisco. Am. J. Public Health 77:169-172.
Curran, J. W., D. N. Lawrence, H. Jaffe, J. E. Kaplan, L. D. Zyla, M. Chamberland, R.
Weinstein, K.-J. Lui, L. B. Schonberger, T. J. Spira, W. J. Alexander, G. Swinger, A.
Ammann, S. Solomon, D. Auerbach, D. Mildvan, R. Stoneburner, J. M. Jason, H. W.
Haverkos, and B. L. Evatt. 1984. Acquired immunodeficiency syndrome (AIDS) associ-
ated with transfusions. N. Engl. J. Med. 310:69-75.
OCR for page 54
54 CONFRONT7NGAiDS:UPDATE~g88
Curran, J. W., H. W. Jaffe, A. M. Hardy, W. M. Morgan, R. M. Selik, and T. J. Dondero.
1988. Epidemiology of HIV infection and AIDS in the United States. Science
239:610-616.
Darrow, W. W., D. F. Echenberg, H. W. Jaffe, P. M. O'Malley, R. H. Byers, J. P. Getchell,
and J. W. Curran. 1987. Risk factors for human immunodeficiency virus (HIV) infections
in homosexual men. Am. J. Public Health 77:479-483.
De Gruttola, V., and S. W. Lagakos. 1987. The value of doubling time in assessing the course
of the AIDS epidemic. Paper prepared for the Institute of Medicine Workshop on Modeling
the Spread of Infection with Human Immunodeficiency Virus and the Demographic Impact of
Acquired Immune Deficiency Syndrome, Washington, D.C., October 15-17.
De Gruttola, V., and K. H. Mayer. 1988. Assessing and modeling heterosexual spread of the
human immunodeficiency virus in the United States. Rev. Infect. Dis. 10:138-150.
Des Jarlais, D. C., S. R. Friedman, M. Marmor, H. Cohen, D. Mildvan, S. Yancovitz, U.
Mathur, W. El-Sadr, T. J. Spira, J. Garber, S. T. Beatrice, A. S. Abdul-Quader, and J. L.
Sotheran. 1987. Development of AIDS, HIV seroconversion, and potential cofactors for
T4 cell loss in a cohort of intravenous drug users. AIDS 1: 105-111.
Des Jarlais, D. C., S. R. Friedman, and R. L. Stoneburner. 1988. HIV infection and
intravenous drug use: Critical issues in transmission dynamics, infection outcomes, and
prevention. Rev. Infect. Dis. 10:151-158.
Dondero, T. J., M. Pappaioanou, and J. W. Curran. 1988. Monitoring the levels and trends
of HIV infection: The Public Health Service's HIV Surveillance Program. Public Health
Rep. 103:213-220.
Eyster, M. E., M. H. Gail, J. O. Ballard, H. Al-Mondhiry, and J. J. Goedert. 1987. Natural
history of human immunodeficiency virus infections in hemophiliacs: Effects of T-cell
subsets, platelet counts, and age. Ann. Intern. Med. 107:1-6.
Fischl, M. A., G. M. Dickinson, G. B. Scott, N. Klimas, M. A. Fletcher, and W. Parks.
1987. Evaluation of heterosexual partners, children, and household contacts of adults with
AIDS. J. Am. Med. Assoc. 257:640-644.
Friedland, G. H., and R. S. Klein. 1987. Transmission of the human immunodeficiency
virus. N. Engl. J. Med. 317:1125-1135.
Gerberding, J. L., C. E. Bryant-LeBlanc, K. Nelson, A. R. Moss, D. Osmond, H. F.
Chambers, J. R. Carlson, W. L. Drew, J. A. Levy, and M. A. Sande. 1987. Risk of
transmitting the human immunodeficiency virus, cytomegalovirus, and hepatitis B virus to
health care workers exposed to patients with AIDS and AIDS-related conditions. J.
Infect. Dis. 156:1-8.
Goedert, J. J., and W. A. Blattner. In press. The epidemiology and natural history of human
immunodeficiency virus. In AIDS: Etiology, Diagnosis, Treatment and Prevention, 2nd
ea., V. T. DeVita, S. Hellman, and S. A. Rosenberg, eds. Philadelphia: Lippincott.
Goedert, J. J., M. E. Eyster, R. J. Biggar, and W. A. Blattner. 1987. Heterosexual
transmission of human immunodeficiency virus: Association with severe depletion of
T-helper lymphocytes in men with hemophilia. AIDS Res. Hum. Retrovir. 3:355-361.
Grant, R. M., J. A. Wiley, and W. Winkelstein. 1987. Infectivity of the human immunode-
ficiency virus: Estimates from a prospective study of homosexual men. J. Infect. Dis.
156: 189-193.
Guinan, M. E., and A. Hardy. 1987. Epidemiology of AIDS in women in the United States:
1981 through 1986. J. Am. Med. Assoc. 257:2039-2042.
Harris, J. E. 1987. The AIDS epidemic: Looking into the 1990s. Technol. Rev. 90:59-64.
Hearst, N., and S. B. Hulley. 1988. Preventing the heterosexual spread of AIDS. Are we
giving our patients the best advice? J. Am. Med. Assoc. 259:2428-2432.
Henderson, D. K., A. J. Saah, B. J. Zak, R. A. Kaslow, H. C. Lane, T. Folks, W. C.
Blackwelder, J. Schmitt, D. J. LaCamera, H. Masur, and A. S. Fauci. 1986. Risk of
OCR for page 55
HIV INFECTION AND ITS EPIDEMIOLOGY 55
nosocomial infection with human T-cell lymphotropic virus type III/lymphadenopathy-
associated virus in a large cohort of intensively exposed health care workers. Ann. Intern.
Med. 104:644-647.
Hoff, R., V. P. Berardi, B. J. Weiblen, L. Mahoney-Trout, M. L. Mitchell, and G. F. Grady.
1988. Seroprevalence of human immunodeficiency virus among childbearing women.
Estimation by testing samples of blood from newborns. N. Engl. J. Med. 318:525-530.
Johnson, A. M. 1988. Heterosexual transmission of human immunodeficiency virus. Br.
Med. J. 296:1017-1020.
Kingsley, L. A., R. Kaslow, C. R. Rinaldo, Jr., K. Detre, N. Odaka, M. VanRaden, R.
Detels, B. F. Polk, J. Chmiel, S. F. Kelsey, D. Ostrow, and B. Visscher. 1987. Risk
factors for seroconversion to human immunodeficiency virus among male homosexuals.
Lancet 1:345-349.
Kreiss, J. K., D. Koech, F. A. Plummer, K. K. Homles, M. Lightfoote, P. Plot, A. R.
Ronald, J. O. Ndinya-Achola, L. J. D'Costa, P. Roberts, E. N. Ngugi, and T. C. Quinn.
1986. AIDS virus infection in Nairobi prostitutes. Spread of the epidemic to east Africa.
N. Engl. J. Med. 314:414-418.
Marmor, M., D. C. Des Jarlais, H. Cohen, S. R. Friedman, S. T. Beatrice, N. Dubin, W.
El-Sadr, D. Mildvan, S. Yancovitz, U. Mathur, and R. Holzman. 1987. Risk factors for
infection with human immunodeficiency virus among intravenous drug abusers in New
York City. AIDS 1:39-44.
Medley, G. F., R. M. Anderson, D. R. Cox, and L. Billard. 1987. Incubation period of AIDS
in patients infected via blood transfusion. Nature 328:719-721.
Mok, J. Q., C. Giaquinto, A. De Rossi, I. Grosch-Worner, A. E. Ades, and C. S. Peckham.
1987. Infants born to mothers seropositive for human immunodeficiency virus. Prelimi-
nary findings from a multicentre European study. Lancet 1:1164-1168.
Morgan, W. M., and J. W. Curran. 1986. Acquired immunodeficiency syndrome: Current
and future trends. Public Health Rep. 101:459-465.
Moss, A. R. 1987. AIDS and intravenous drug use: The real heterosexual epidemic. Br.
Med. J. 294:389-390.
Moss, A. R., D. Osmond, P. Bacchetti, J.-C. Chermann, F. Barre-Sinoussi, and J. Carlson.
1987. Risk factors for AIDS and HIV seropositivity in homosexual men. Am. J.
Epidemiol. 125:1035-1047.
Moss, A. R., P. Bacchetti, D. Osmond, W. Krampf, R. E. Chaisson, D. Stites, J. Wilber,
J.-P. Allain, and J. Carlson. 1988. Seropositivity for HIV and the development of AIDS
or AIDS related condition: Three-year follow-up of the San Francisco General Hospital
cohort. Br. Med. J. 296:745-750.
Novick, D. M., M. J. Kreek, D. C. Des Jarlais, T. J. Spira, E. T. Khuri, J. Ragunath, V. S.
Kalyanaraman, A. M. Gelb, and A. Miescher. 1986. Abstract of clinical research findings:
Therapeutic and historical aspects. Pp. 318-320 in Proceedings of the 47th Annual
Scientific Meeting, Committee on Problems of Drug Dependence (1985), L. Harris, ed.
Rockville, Md.: National Institute on Drug Abuse.
Novick, L. F., D. Berns, R. Stricof, and R. Stevens. 1988. New York State l~epartment of
Health newborn seroprevalence study. Interim report draft. Albany. March 15.
Nzilambi, N., R. W. Ryder, F. Behets, H. Francis, E. Bayende, A. Nelson, J. M. Mann, et
al. 1987. Perinatal HIV transmission in two African hospitals. P. 158 in Abstracts of the
Third International Conference on AIDS, Washington, D.C., June 1-5.
Padian, N. S. 1987. Heterosexual transmission of acquired immunodeficiency syndrome:
International perspectives and national projections. Rev. Infect. Dis. 9:947-960.
Padian, N., L. Marquis, D. P. Francis, R. E. Anderson, G. W. Rutherford, P. M. O'Malley,
and W. Winkelstein, Jr. 1987a. Male-to-female transmission of human immunodeficiency
virus. J. Am. Med. Assoc. 258:788-790.
OCR for page 56
56 CONFRONTING AIDS: UPDATE Eggs
Padian, N., J. Wiley, and W. Winkelstein. 1987b. Male-to-female transmission of human
immunodeficiency virus (HIV): Current results, infectivity rates, and San Francisco
population seroprevalence estimates. P. 171 in Abstracts of the Third International
Conference on AIDS, Washington, D.C., June 1-5.
Peterman, T. A., R. L. Stoneburner, J. R. Allen, H. W. Jaffe, and J. W. Curran. 1988. Risk
of human immunodeficiency virus transmission from heterosexual adults with transfusion-
associated infections. J. Am. Med. Assoc. 259:55-58.
Piot, P., F. A. Plummer, F. S. Mhalu, J.-L. Lamboray, J. Chin, and J. M. Mann. 1988.
AIDS: An international perspective. Science 239:573-579.
Quinn, T. C., J. M. Mann, J. W. Curran, and P. Piot. 1986. AIDS in Africa: An
epidemiologic paradigm. Science 234:955-963.
Quinn, T. C., P. Piot, J. B. McCormick, F. M. Feinsod, H. Taelman, B. Kapita, W.
Stevens, and A. S. Fauci. 1987. Serologic and immunologic studies in patients with AIDS
in North America and Africa. The potential role of infectious agents as cofactors in human
immunodeficiency virus infection. J. Am. Med. Assoc. 257:2617-2621.
Robertson, J. R., A. B. V. Bucknall, P. D. Welsby, J. J. K. Roberts, J. M. Inglis, J. F.
Peutherer, and R. P. Brettle. 1986. Epidemic of AIDS related virus (HTLV-III/LAV)
infection among intravenous drug abusers. Br. Med. J. 292:527-529.
Schoenbaum, E. E., P. A. Selwyn, D. Hartel, R. S. Klein, K. Davenny, and G. H.
Friedland. 1987. HIV seroconversion in intravenous drug abusers: Rate and risk factors.
P. 117 in Abstracts of the Third International Conference on AIDS, Washington, D.C.,
June 1-5.
Ward, J. W., D. A. Deppe, S. Samson, H. Perkins, P. Holland, L. Fernando, P. M. Feorino,
P. Thompson, S. Kleinman, and J. R. Allen. 1987. Risk of human immunodeficiency virus
infection from blood donors who later developed the acquired immunodeficiency syn-
drome. Ann. Intern. Med. 106:61-62.
Ward, J. W., S. D. Holmberg, J. R. Allen, D. L. Cohn, S. E. Critchley, S. H. Kleinman, B.
A. Lenes, O. Ravenholt, J. R. Davis, M. G. Quinn, and H. W. Jaffe. 1988. Transmission
of human immunodeficiency virus (HIV) by blood transfusions screened as negative for
HIV antibody. N. Engl. J. Med. 318:473-478.
Winkelstein, W., Jr. 1988. Epidemiological observations on the causal nature of the
association between infection by the human immunodeficiency virus and the acquired
immunodeficiency syndrome. Paper presented at the Scientific Forum on the Etiology of
AIDS, American Foundation for AIDS Research, Washington, D.C., April 9.
Winkelstein, W., Jr., M. Samuel, N. S. Padian, J. A. Wiley, W. Lang, R. E. Anderson, and
J. A. Levy. 1987a. The San Francisco Men's Health Study. III. Reduction in human
immunodeficiency virus transmission among homosexual/bisexual men, 1982-86. Am. J.
Public Health 76:685-689.
Winkelstein, W., Jr., D. M. Lyman, N. Padian, R. Grant, M. Samuel, J. A. Wiley, R. E.
Anderson, W. Lang, J. Riggs, and J. A. Levy. 1987b. Sexual practices and risk of
infection by the human immunodeficiency virus. The San Francisco Men's Health Study.
J. Am. Med. Assoc. 257:321-325.
Representative terms from entire chapter:
human immunodeficiency
