HIV Transmission and Other Sexually Transmitted Diseases

Key to the understanding of different patterns of spread worldwide are differences in the relative efficiency of heterosexual transmission of AIDS. In the United States, heterosexual contact is relatively inefficient in spreading HIV, with a possibility of conversion estimated at approximately 0.2% with a single sexual contact. In comparison, an infected prostitute in Nairobi may have an HIV transmission rate of 8% with a single sexual contact, rising to 28% if the male was uncircumcised and a genital ulcer was acquired at the same time.

The rate of heterosexual AIDS transmission is significantly increased if the couple (or one partner) already has an ulcerative sexually transmitted disease. This may affect HIV transmission in one of three ways. First, genital ulcers may increase the infectivity of the donor because of blood or serum from the ulcerated area. Second, open sores may increase the susceptibility of the recipient, both due to nonintact skin or mucosa and also because there may be an increased number of CD4 cells at the ulcer site, making cross-infection easier. Finally, various diseases may be cofactors in any HIV initial infection or progression from increased activation of T4 lymphocytes leading to increased production of HIV-infected cells and viral copies.

The sexually transmitted diseases associated with increased HIV infection include syphilis, chancroid, lymphogranuloma venereum, and herpes simplex. These are all common in most areas in which heterosexual transmission occurs. Chlamydia trachomatis is a possible cofactor. Gonorrhea and genital warts, as well as various other nonulcerative sexually transmitted diseases, probably do not increase susceptibility to or transmission of HIV. The incidence of non-AIDS sexually transmitted diseases observed in antenatal clinics in Malawi has been measured by Maher and Hoffman at 42%, with a 32% HIV-positive rate.

Men who have not been circumcised are at increased risk of HIV infection (odds ratio 4.8), with countries in which circumcision is rare closely matching the countries of the "AIDS belt" in Africa. The effect may be due to an increased incidence of ulcerative STDs such as chancroid in uncircumcised males, as well as other factors related to hygiene or a more favorable environment for viral survival and transmission. The relative risk is so striking that some believe circumcision should be considered as an intervention strategy for AIDS control.