Lopping off foreskins reduces HIV transmission. But we haven’t always known that. Indeed when I was in grad school (not ALL that long ago) I remember being given a paper overlaying a map of tribal circumcision practices in Africa with HIV rates. The paper concluded that circumcision might slow the spread of HIV; it was held up as an example of bad epidemiology.
HIV is low where circumcision is high, yes, just as TB is low where Mercedes ownership is high. But that doesn’t mean circumcision protects you from HIV any more than driving a Merc protects you from TB. And then the lecture about confounding factors such as religion, which may affect both the “explanation” — circumcision — and the thing we’re trying to explain — HIV. Leading to next week’s lecture, about how all will be neatly explained by the randomised controlled trial, the Rolls Royce of study designs.
It may have been a weak paper, but it turns out it was true. We know that because colleagues did go on to do the Rolls Royce studies, randomly assigning some guys to get snipped and others to stay in one piece. The men who lost their foreskins were 60% less likely to get HIV than the men who didn’t go under the knife. According to Jeffrey Klausner and colleagues, writing in Future Medicine, “male circumcision is the only modality for preventing sexual HIV transmission that has been proven to work by the highest standards of scientific evidence; specifically, findings from multiple randomized controlled trials”.
Hang on a minute. That implies that other methods have been proven not to work. But that is absolutely not true. Condom promotion has worked exceptionally well in many settings, most famously in the brothels of Thailand, slashing new sexual infections from nearly 120,000 a year in 1989 to 12,000 a year in 2005 (see AIDS in Asia: warning – gargantuan pdf file). It hasn’t been shown to work by the “highest standards of scientific evidence” precisely because it IS so efficient. We KNOW condoms work to prevent the spread of HIV. It would therefore be unethical to randomly assign people who might be at risk for infection to a “No condom use” group, just for the sake of the highest standards if scientific evidence. Sometimes, common sense trumps randomised controlled trials. If you’re not convinced, please read the British Medical Journal’s seminal paper: Parachute use to prevent death and major trauma related to gravitational
challenge: systematic review of randomised controlled trials