Case studies of bias in real life epidemiologic studies Bias File 9. Male circumcision for HIV prevention: from confounding to causality Compiled by Madhukar Pai, MD, PhD Jay S Kaufman, PhD Department of Epidemiology, Biostatistics & Occupational Health McGill University, Montreal, Canada
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[email protected] THIS CASE STUDY CAN BE FREELY USED FOR EDUCATIONAL PURPOSES WITH DUE CREDIT 1 Bias File 9. Male circumcision for HIV prevention The story of male circumcision for HIV prevention is a long and fascinating one. Ecological studies in the 1980s and early 1990s provided early evidence that in African countries where male circumcision is practised, HIV seroprevalence was considerably lower than in areas where it is not practised. For example, Moses and others published an ecological study using data from 41 countries in Africa, with results supporting this hypothesis (figure). In the 1990s and early 2000s, a large number of observational studies were done, mostly cross-sectional studies (e.g. Auvert B et al. AIDS 2001), with a few case- control (e.g. Quigley M et al. AIDS 1997) and cohort (e.g. Gray RH et al. AIDS 2000) studies. Although many of these observational studies showed a protective effect of circumcision, they were highly controversial because of concerns about bias and confounding. In 2005, a systematic review was published in the Lancet Infectious Diseases by Siegfried et al., and this review included 37 observational studies on circumcision and HIV. At that time, there were no published randomized controlled trials (RCTs) on this topic. The review concluded that "although most studies show an association between male circumcision and prevention of HIV, these results may be limited by confounding, which is unlikely to be adjusted for." The panel from the paper by Siegfried provides a list of potential confounding variables.