APPENDIX C
Glossary

A

Acute disseminated encephalomyelitis.

A clinical syndrome characterized by acute depression of consciousness and multifocal neurologic findings that usually occur a few days or weeks following vaccine administration or virus-like disease. It is characterized pathologically by diffuse loci of perivenular inflammation and demyelination. See Chapter 3.

ADEM.

See Acute disseminated encephalomyelitis.

Anaphylaxis.

Generalized anaphylaxis is an acute, often explosive, systemic reaction characterized by pruritus, generalized flush, hives, respiratory distress, and vascular collapse and, occasionally, by seizures, vomiting, abdominal cramps, and incontinence. It occurs in a previously sensitized person who again receives the sensitizing antigen. See Chapter 4.

Arthralgia.

Pain in a joint or joints.

Arthritis.

Inflammation of a joint or joints detectable as swelling, redness, and tenderness.

Arthropathy.

Any joint disease.

Arthus reaction.

A reaction that follows injection of an antigen into an animal in which hypersensitivity has been previously established and that involves infiltrations, edema, sterile abscesses, and in severe cases, gangrene. See Chapter 4.

Aseptic meningitis.

An inflammation of the meninges with typical changes in the cerebrospinal fluid, including increased numbers of leukocytes, normal glucose, and absence of bacteria on examination and culture.



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Adverse Events Associated with Childhood Vaccines: Evidence Bearing on Causality APPENDIX C Glossary A Acute disseminated encephalomyelitis. A clinical syndrome characterized by acute depression of consciousness and multifocal neurologic findings that usually occur a few days or weeks following vaccine administration or virus-like disease. It is characterized pathologically by diffuse loci of perivenular inflammation and demyelination. See Chapter 3. ADEM. See Acute disseminated encephalomyelitis. Anaphylaxis. Generalized anaphylaxis is an acute, often explosive, systemic reaction characterized by pruritus, generalized flush, hives, respiratory distress, and vascular collapse and, occasionally, by seizures, vomiting, abdominal cramps, and incontinence. It occurs in a previously sensitized person who again receives the sensitizing antigen. See Chapter 4. Arthralgia. Pain in a joint or joints. Arthritis. Inflammation of a joint or joints detectable as swelling, redness, and tenderness. Arthropathy. Any joint disease. Arthus reaction. A reaction that follows injection of an antigen into an animal in which hypersensitivity has been previously established and that involves infiltrations, edema, sterile abscesses, and in severe cases, gangrene. See Chapter 4. Aseptic meningitis. An inflammation of the meninges with typical changes in the cerebrospinal fluid, including increased numbers of leukocytes, normal glucose, and absence of bacteria on examination and culture.

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Adverse Events Associated with Childhood Vaccines: Evidence Bearing on Causality The most common causes include viral infection and noninfectious causes such as lead poisoning. Attenuated. Having decreased virulence; used especially for live virus vaccines. Attenuation is achieved either through selection of less virulent mutants or through physiologic alteration by exposure to unfavorable conditions. Attributable risk (exposed). The rate of a disease or other outcome in exposed individuals that can be attributed to the exposure. Synonymous with risk difference and excess risk. This measure is estimated by subtracting the rate of the outcome (usually incidence or mortality) among unexposed individuals from the rate among exposed individuals. It is assumed that causes other than the one under investigation have had equal effects on exposed and unexposed groups and that the effects of different causes are additive. This term is often used, incorrectly, to denote the attributable fraction among exposed individuals in the population. B Bayes theorem. A theorem in probability theory. In epidemiology, it is used to obtain the probability of disease in a group of people with some characteristic on the basis of the overall rate of that disease (the prior probability of disease) and of the likelihoods of that characteristic in healthy and diseased individuals. The most familiar application is in clinical decision analysis where it is used for estimating the probability of a particular diagnosis given the appearance of some symptom or test result. Bias. Deviation of results or inferences from the truth, or processes leading to such deviation. Any trend in the collection, analysis, interpretation, publication, or review of data that can lead to conclusions that are systematically different from the truth. Not to be confused with prejudice or partisan point of view, as is the conventional usage. Brachial neuritis. Also known as brachial plexus neuropathy or as neuralgic amyotrophy. A neuropathy which presents as a deep, steady, often severe aching pain in the shoulder and upper arm. See Chapter 3. C Case-control study (Syn: case-comparison study). A controlled observational study that starts with the identification of persons with the disease or condition (adverse event) of interest and a suitable control (comparison) group of persons without the disease. The relation of an attribute (e.g., immunization) to the disease is examined by comparing the diseased and nondiseased groups with regard to how frequently the attribute is present, or if quantitative, the levels of the attribute, in each of the groups. Cohort study. (Syn: prospective, follow-up study). A controlled observational study in which subsets of a defined population can be identified who

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Adverse Events Associated with Childhood Vaccines: Evidence Bearing on Causality are, have been, or in the future may be exposed or not exposed, or exposed in different degrees, to a factor or factors hypothesized to influence the probability of occurrence of a given disease (adverse event) or other outcome. The essential feature of the cohort design is observation of the population for a sufficient length of time to generate reliable incidence or mortality rates. Confidence interval. A range of values estimated for a given variable. The range has a specified probability, e.g., 95 percent, of including the true value of the variable. The specified probability is called the confidence level. Controlled study. Controlled studies are studies that use a comparison group that differs from the subjects of the study in either disease experience (outcome) or allocation to a regimen (exposure). Allocation to a regimen can be random, as in a randomized clinical trial, or nonrandom, as in an observational cohort study or a case-control study. E EAE. See Experimental allergic encephalomyelitis. EAN. See Experimental allergic neuritis. Ecologic study. A study in which the units of analysis are populations or groups of people, rather than individuals. Encephalitis. Refers to an encephalopathy caused by an inflammatory response in the brain. This is usually manifested with systemic constitutional symptoms, particularly fever and pleocytosis of the cerebrospinal fluid. However, the terms encephalopathy and encephalitis have been used imprecisely and even interchangeably in the literature. Encephalopathy. Refers to a variety of conditions affecting the brain resulting in alterations in the level of consciousness, ranging from stupor to coma. At times, febrile seizures, afebrile seizures, and epilepsy have been considered components of encephalopathy. However, the terms encephalopathy and encephalitis have been used imprecisely and even interchangeably in the literature. See Chapter 3. Erythema multiforme. An inflammatory eruption characterized by symmetrical erythematous, or edematous lesions of the skin or mucous membranes. It is usually nonpruritic, lasts several days, and leaves no sequelae. Stevens-Johnson syndrome is a rare, severe, potentially fatal form of erythema multiforme that is associated with bullous lesions. Experimental allergic encephalomyelitis. Also known as EAE. An experimental model for acute disseminated encephalomyelitis. See Chapter 3. Experimental allergic neuritis. Also known as EAN. An experimental model of Guillain-Barré syndrome. See Chapter 3. G GBS. See Guillain-Barré syndrome.

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Adverse Events Associated with Childhood Vaccines: Evidence Bearing on Causality Guillain-Barré syndrome. Also known as postinfectious neuritis or acute inflammatory demyelinating polyneuritis, it is a syndrome characterized by rapid onset of flaccid motor weakness with depression of tendon reflexes and inflammatory demyelination of peripheral nerves. Commonly abbreviated as GBS. See Chapter 3. H Haemophilus influenzae. A haemophilus found normally in the human nasopharynx; the influenza bacillus. Strains with polysaccharide capsules, of six types (designated a to f), may cause disease. Type b is the most frequent. The organism was the commonest cause of meningitis in children before introduction of the vaccine against the organism. It also causes sinusitis, otitis media, pneumonia, arthritis, and a fulminating epiglottitis and obstructive laryngitis. The organism was once considered, mistakenly, the cause of pandemic influenza. Also called Pfeiffer's bacillus. Hepatitis B. Inflammation of the liver caused by hepatitis B virus. The infectious agent may circulate in the blood for long periods of time (months or years) and is characteristically transmitted by parenteral, percutaneous, or permucosal inoculation of even minute amounts of blood, blood products, or bodily secretions. The disease may be acute or chronic, symptomatic or asymptomatic. Also called viral hepatitis type B, homologous serum hepatitis, human serum jaundice, and homologous serum jaundice. Hepatitis B virus. A virus of an unnamed family that is composed of a membrane-bound particle called a Dane particle containing double-stranded circular DNA and a DNA polymerase. It is one of the major causes of posttransfusion hepatitis. Human disease can be characterized by acute or chronic hepatitis or an asymptomatic carrier state. Transmission is predominantly via parenteral routes or contact with infected blood. Also called serum hepatitis virus (outmoded). I Immunization. The process of rendering a subject immune or of becoming immune. In this report the term has been accepted to be synonymous with vaccination. See Vaccination. active i. Inoculation with a specific antigen to induce an immune response. passive i. The conferral of specific immunity by the administration of sensitized lymphoid cells or serum from immune individuals. Inactivate. To make biologically inactive, as viruses or bacteria, toxins, or serum complement, by any of various means, such as by physical means (exposure to X rays, ultraviolet irradiation, or heating) or by exposure to chemical agents or to immunologic antagonists.

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Adverse Events Associated with Childhood Vaccines: Evidence Bearing on Causality Inactivated polio vaccine (IPV). A sterile suspension of three types of inactivated polioviruses. The viruses are grown separately in monkey renal tissue cultures and are then inactivated and combined. The vaccine is administered subcutaneously and confers active immunity against poliomyelitis. Also called Salk vaccine and killed poliovirus vaccine. Infantile spasms. A condition characterized by sudden flexion of the arms, forward flexion of the trunk, and extension of the legs. The attacks last only a few seconds but may be repeated many times a day. They are restricted to the first 3 years of life, often to be replaced by other forms of seizures. Insulin-dependent diabetes mellitus. Also known as juvenile diabetes or type I diabetes. A disease characterized most frequently by low or absent levels of circulating endogenous insulin. See Chapter 7. IPV. See Inactivated Polio vaccine. J Juvenile diabetes. An autoimmune disease characterized most frequently by low or absent levels of circulating endogenous insulin (more properly called insulin-dependent diabetes mellitus). K Koch's postulates. Koch stated that these postulates should be met before a causative relationship between a particular bacterial parasite or disease agent and the disease in question can be accepted. 1. The agent must be shown to be present in every case of the disease by isolation in pure culture. 2. The agent must not be found in cases of other diseases. 3. Once isolated, the agent must be capable of reproducing the disease in experimental animals. 4. The agent must be recovered from the experimental disease produced. M Monitoring System for Adverse Events Following Immunization (MSAEFI ). A passive surveillance system designed and monitored by the Centers for Disease Control for the purpose of collecting nationwide data on adverse events temporally associated with receipt of vaccines purchased with federal, state, or local government funds. See Vaccine Adverse Event Reporting System. Mononeuropathy. Neuropathic dysfunction limited to the distribution of a single peripheral nerve that is large enough to be named. See Chapter 3. MSAEFI. See Monitoring System for Adverse Events Following Immunization. Multiple sclerosis. A chronic central nervous system demyelinating disease in which the lesions occur in multiple locations and at different times.

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Adverse Events Associated with Childhood Vaccines: Evidence Bearing on Causality O Odds ratio (OR). In studies of adverse events following immunization, the odds ratio generally refers to the exposure-odds ratio, which, for a set of case-control data, is the ratio of the odds of exposure among the cases to the odds of exposure among controls (noncases). When the adverse event under study is rare, the odds ratio is a good estimate of the relative risk. Optic neuritis. Represents a central demyelinating disease of the optic nerve anterior to the optic chiasm. It can occur as a solitary unexplained monophasic disease or it may be an early sign of multiple sclerosis. See Chapter 3. P Paralytic poliomyelitis. A paralytic disease caused by invasion of the poliovirus into the central nervous system and death of nerve cells in the anterior horn of the spinal cord, the brainstem, and in the motor cortex. The muscle paralysis is usually asymmetrical. Peripheral mononeuropathy. See Mononeuropathy. R Relative risk (RR). The ratio of the risk of disease, death, or other outcome among the exposed to the risk among the unexposed. Generally derived from controlled cohort studies or clinical trials. If used in conjunction with adverse events following immunization, when the adverse event under study is rare, the odds ratio is a good estimate of the RR. Residual seizure disorder. Recurrent, afebrile seizures; also known as epilepsy. Reye syndrome. An acute and occasionally fatal childhood syndrome of encephalopathy and fatty degeneration of the liver marked by rapid development of brain swelling and altered levels of consciousness. Risk difference. See attributable risk. S Sensorineural deafness. A form of hearing loss resulting from pathologic changes in the end organ structures within the cochlea or in the neural connections between the cochlea and the cochlear nuclei. See Chapter 3. Stevens-Johnson syndrome. See Erythema multiforme. Serum sickness. Caused by interaction between antigen and antibody in the circulation with the formation of antigen-antibody complexes in an environment of antigen excess. Symptoms include urticaria, swelling, arthritis, and fever. See Chapter 4. Subacute sclerosing panencephalitis (SSPE). A rare form of encephalitis involving both grey and white matter that can affect children and adolescents that is characterized by insidious onset of a progressive cerebral dysfunction occurring over the course of weeks or months. See Chapter 3. Sudden infant death syndrome (SIDS). The unexpected and unexplained death of an apparently well, or virtually well, infant. SIDS is the most

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Adverse Events Associated with Childhood Vaccines: Evidence Bearing on Causality common cause of death of infants between ages 2 weeks and 1 year, accounting for one-third of all deaths in this age group. T Thrombocytopenia. A severe decrease in the number of platelets, the cells involved in clotting. Thrombocytopenia may stem from failure of platelet production, splenic sequestration of platelets, increased platelet destruction, increased platelet utilization, or dilution of platelets. Thrombocytopenic purpura. Severe thrombocytopenia characterized by mucosal bleeding and bleeding into the skin in the form of multiple petechiae, most often evident on the lower legs, and scattered small ecchymoses (bruises) at sites of minor trauma. In children, idiopathic thrombocytopenic purpura is usually self-limited and follows a viral infection. Transverse myelitis. A clinical syndrome characterized by the acute onset of signs of spinal cord disease, usually involving the descending motor tracts and the ascending sensory fibers, suggesting a lesion at one level of the spinal cord. It can occur in isolation or as part of a multifocal demyelinating disease such as multiple sclerosis or acute disseminated encephalomyelitis. See Chapter 3. V Vaccination. Inoculation with a vaccine for the purposes of inducing immunity. In this report the term has been accepted to be synonymous with immunization. See Immunization. Vaccine. A material containing live attenuated or killed microorganisms, or constituents of microorganisms, capable of eliciting protection against infection. Vaccine Adverse Event Reporting System (VAERS). A passive surveillance system intended to collect reports of reactions to vaccines that is under the aegis of the Centers for Disease Control and Prevention and the U.S. Food and Drug Administration. This system replaces the Monitoring System for Adverse Events Following Immunization (MSAEFI) and a similar system formerly run by the Food and Drug Administration. See Chapter 10. VAERS. See Vaccine Adverse Event Reporting System.