The authors point to 32 studies from eight countries that found a significant association between lack of male circumcision and HIV infection. Recent findings from three additional countries reported similar results. In addition, dramatic discrepancies in regional HIV infection rates can be partially explained by circumcision practices, say the authors. In most West African countries, for example, where male circumcision is a widespread practice, HIV prevalence levels are between one and five percent. In comparison, many of the predominately non-circumcising East and South African nations have infection rates approaching 25 percent.
Similar patterns exist in South and Southeast Asia.
Halperin and Bailey estimate that in countries like Nigeria and Indonesia, where no more than a fifth of the men are uncircumcised, roughly 25 percent of HIV infections can be explained by a lack of circumcision. This number jumps to 55 percent for countries such as Zambia and Thailand, where 80 percent or more of men are uncircumcised. The increased risk of infection is attributable to the foreskin of the penis which provides a vulnerable portal of entry to HIV and other pathogens. An intact foreskin also exposes a man to other sexually transmitted diseases such as syphilis, herpes, and chancroid that are known cofactors for HIV infection. Anecdotal evidence suggests that circumcision could lead to better protection against HIV through an increased use of condoms as well, says Halperin.