transmitting STDs, such as gender and other preexisting or concurrent STDs including HIV infection, were discussed. Other biological factors that contribute to the spread of STDs include the lack of conspicuous signs and symptoms manifested by infected persons, the long lag time from initial infection to signs of severe complications, and the propensity of STDs to more easily infect young women and female adolescents than men. In addition, the committee summarizes the potential impact of male circumcision, vaginal douching, risky sexual practices, and other factors on the spread of STDs or risk of sequelae.

Asymptomatic Infections

As discussed in Chapter 2, many STDs either do not produce acute symptoms or clinical signs of disease or do not produce symptoms sufficiently severe for an infected individual to seek medical attention. For example, as many as 85 percent of women with chlamydial infection are asymptomatic (Fish et al., 1989; Judson, 1990; Stamm et al., 1990). A study of college women seen for routine gynecological examinations found that 79 percent of those who tested positive for chlamydial had no symptoms of disease (Keim et al., 1992). Asymptomatic infection also contributes to the spread of viral STDs including HIV infection, hepatitis B virus infection, genital herpes, and human papillomavirus infection. HIV infection is a prime example of how certain STDs that may go unrecognized for many years allow wide dissemination of infection before it is detected and treated. Lack of awareness that most cases of certain STDs are asymptomatic or otherwise unrecognized leads many susceptible persons to falsely believe that it is possible to tell whether a potential partner is infected with an STD, and similarly explains why many infected asymptomatic persons fail to take precautions to avoid transmitting their infection. Even when symptoms are present, many STDs have nonspecific signs and symptoms, making them difficult to diagnose without laboratory tests. Asymptomatic infection, therefore, is an extremely important biological factor that reduces the likelihood that infected individuals will seek health care and/or receive appropriate diagnoses. This hinders detection and treatment of the infection, increases the period of infectiousness, and thereby promotes the spread of the infection.

Lag Time to Complications

Another biological factor that contributes to the STD epidemic is the long period of time (sometimes years or decades) from initial infection until the appearance of clinically significant problems. The best examples of sexually transmitted pathogens and complications that have long lag times are (a) human papillomavirus and cervical cancer and (b) hepatitis B virus and liver cancer. In both instances, the initial phase of the infection is often asymptomatic and creates obstacles to detection and treatment, as noted above. In addition, the clinical



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