Wednesday, 21 October 2009

Foreskin surface area and HIV risk

The African randomised controlled trials were amazingly productive. Not only were the direct results of the trials (namely proving the causative effect of circumcision in reducing HIV risk) important, but they also provided an environment for many interesting piggy-back studies.

This is an interesting new paper. Entitled "Foreskin surface area and HIV acquisition in Rakai, Uganda (size matters)", it is essentially an analysis of the relationship between the surface area of the foreskin and the risk of HIV infection among control-arm participants in two of the HIV RCTs.

Here's the key finding:
Mean foreskin surface area was significantly higher among men who acquired HIV (43.3 cm2, standard error 2.1) compared with men who remained uninfected (36.8 cm, standard error 0.5, P = 0.01).
This is logical, really: given that the foreskin increases the risk of HIV infection, one would expect more foreskin to further increase the risk. It might, in principle, be information that would be useful in targetting circumcision: men with longer foreskins could, for example, be warned that their risk is greater. But the information will prove most useful, I believe, in helping researchers as they continue to investigate the mechanisms by which circumcision is protective.

For those uncomfortable with metric measurements, 43.3 square centimetres is 6.71 square inches, and 36.8 square centimetres is 5.7 square inches. To my knowledge, this is the first study of foreskin surface area in the literature - I have never been able to identify any evidence for the "15 square inches" commonly claimed by the anti-circumcision lobby, which appears to be merely a guess, and apparently a rather over-inflated guess. So now that we have hard data, we can expect to see that figure disappear. I wish I wasn't joking - I've never yet seen the anti-circumcision lobby abandon any of their myths in the face of contrary evidence - but I might be pleasantly surprised.

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