signs of the associated life-threatening cancers usually do not appear until years or decades after the initial infection. Because of this phenomenon, many cases of STD-related cancers and other long-term complications are not attributed to a sexually transmitted infection. At both individual and population levels, the lack of a perceived connection between sexually transmitted infections and these serious complications reduces both the perceived significance of STDs and the motivation to undertake preventive action. Although the lag time between exposure to HIV and development of clinical symptoms of AIDS likewise can be quite long, there is greater awareness of the link between unprotected sex and the risk of acquiring HIV, and ultimately AIDS, compared to other STDs.

Increased Susceptibility of Women and Female Adolescents

Age and gender may influence risk for an STD. Specifically, as mentioned in Chapter 2, young women and female adolescents are more susceptible to STDs compared to their male counterparts because of the biological characteristics of their anatomy (Cates, 1990). This is because in puberty and young adulthood, specific cells (columnar epithelium) that are especially sensitive to invasion by certain sexually transmitted organisms, such as chlamydial and gonococcus, extend from the inner cervix out over the vaginal surface of the cervix, where they are unprotected by cervical mucus. These cells eventually recede into the inner cervix with age.

In addition to biological factors, women and female adolescents may also find it more difficult than men to implement protective behaviors, partly because of the power imbalance between men and women (Elias and Heise, 1994; IOM, 1994). For example, condoms are the most effective protection against STDs for sexually active persons, but the decision whether to use a condom is ultimately up to the male partner, and negotiating condom use may be difficult for women (Rosenberg and Gollub, 1992). The determinants of condom use are discussed in Chapter 4.

Other Biological Factors

Other biological factors that may increase risk for acquiring, transmitting, or developing complications of certain STDs include presence of male penile foreskin, vaginal douching, risky sexual practices, use of hormonal contraceptives or intrauterine contraceptive devices, cervical ectopy, immunity resulting from prior sexually transmitted or related infections, and nonspecific immunity conferred by normal vaginal flora.

Lack of male circumcision seems to increase the risk of acquiring and perhaps transmitting certain STDs. A review of 30 published epidemiological studies that examined the relationship between HIV infection and male circumcision concluded that most studies found a statistically significant association between

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