Some evidence supports the idea that circumcision may biologically aid the prevention of HIV. First, circumcision may change the microbiome of the penis area, decreasing the number of anaerobic bacteria that were present under the foreskin (Price et al., 2010). The decrease in anaerobic microbes may support the infection of Langerhans cells with HIV, which in turn infect CD4+ cells (Sugaya, Loré, Koup, Douek, & Blauvelt, 2004; Krieger, 2012). Interestingly, the foreskin has many more Langerhans cells than do the rectum or urethra (Hussain & Lehner, 1995). Further, the inner foreskin is susceptible to HIV due to its lack of keratinization (Krieger, 2012), which can help protect the skin from microabrasions and is typically present in areas that are exposed to air.
Many observational studies have been conducted in which HIV rates in populations with circumcised penises were compared to populations with uncircumcised penises. An influential meta-analysis conducted in 2000 found a statistically significant protection from HIV among circumcised men (Weiss, Quigley, & Hayes, 2000). Importantly, the study accounted for confounders by adjusting for age, number of sexual partners, contact with sex workers, infection with STDs, condom use, and many other possible confounding factors. Of all of the studies analyzed, there was quite a bit of heterogeneity—likely because a protective effect would vary between populations due to cultural differences, timing of circumcision, and differences in prevalence of STDs (Weiss, Quigley, & Hayes, 2000). While the findings from this meta-analysis are important, observational studies are inherently flawed because there could be potentially unlimited confounders, and those performing the analysis may not include every study conducted on circumcision and HIV.
Since that meta-analysis of observational studies was conducted in 2000, three heavily influential randomized controlled trials have been conducted and have led the WHO and many health organizations to conclude that circumcision reduces the likelihood of contracting HIV by about 60%. The studies are very similar, so here we will examine only one of them in detail (see “other studies” below). The first study, conducted in 2005 in Orange Farm, a region outside Johannesburg, South Africa, found that circumcision reduced an individual’s likelihood of contracting the virus by 61%—even when controlling for behavioral factors, such as sexual behavior, condom use, and health-seeking behavior (Auvert et al., 2005). The study included 2,580 HIV-negative participants. After the participants were circumcised, follow up face-to-face interviews were conducted and participants were asked the following questions: the number of sexual contacts, the date of first and last sexual contact, the frequency of condom use (never, sometimes, always), and the type of partnership (spousal or non-spousal). Participants also received 15-20 minute counseling sessions including information about STIs in general and HIV in particular and on how to prevent the risk of infection. Participants were also encouraged to attend voluntary counseling and testing in a nearby public clinic or in a voluntary counseling and testing center funded by the project and located in the same building as the investigation center. Condoms were provided in the waiting room of the investigation centre and were also provided by the counselor. Additionally, those in control groups were circumcised after the completion of the study (Auvert et al., 2005).
One other interesting question is whether male circumcision protects females. The only study conducted to answer this was conducted in Rakai, Uganda. The study was closed early because it was not going to be able to answer the question with sufficient statistical power. The preliminary results of this clinical trial suggest that if a couple does not abstain from sex until the surgical wound from the man’s circumcision has completely healed, the woman may be at increased risk of acquiring HIV if her partner is HIV positive (Wawer et al., 2009).
Other studies:
(Gray, Kigozi, Serwadda, Makumbi, & al, 2007)
(Bailey, Moses, Parker, Agot, & al, 2007)
Question comes to mind about ethics of only doing these studies in Africa. Generally, it’s considered unethical to perform research on vulnerable populations or ones that may live in poverty with little education because it is easy to coerce individuals to participate. All of these research studies were conducted in Sub-Saharan Africa, in which many areas of poverty and low education lie. Due to the use of monetary rewards for participation, one might caution researchers on coercion tactics.