The Effects of Circumcision on the Penis Microbiome

Here is an interesting study. Using men from the intervention arm of the Ugandan RCT, the researchers studied the microbiological flora of the penis before and after circumcision.

The researchers found that there was a significant change in the types of bacteria found on the penis. In particular, the number of anaerobic bacteria fell significantly following circumcision.

The discovery that circumcision alters the penile flora is nothing new. Many studies have investigated this previously (for an overview see refs 12-22 in my letter here), and have come to similar conclusions.

The authors speculate that the presence of anaerobic bacteria on the uncircumcised penis might promote inflammatory conditions which activate immune cells that, in turn, act as a magnet for HIV.

It also, of course, helps to explain the fact that circumcised males enjoy reduced risk of urinary tract infections and local infections such as balanitis.

Cost-effectiveness of newborn circumcision in reducing lifetime HIV risk among US males.

Here is a fascinating study by researchers from the CDC. Using data from randomised controlled trials, they modelled the effect of neonatal circumcision on lifetime risk of HIV in the United States.

The authors assumed (as far as I can tell) that circumcision had an effect only on heterosexual transmission. This is a conservative assumption, so we should bear in mind that the results will also be conservative estimates.

They found that neonatal circumcision "reduced the 1.87% lifetime risk of HIV among all males by about 16%" (that is, it reduced by about 0.3% to about 1.6%). This effect varied by race, from 7.9% for white men to 20.9% for black men. They also found "lower expected HIV-related treatment costs and a slight increase in [Quality-adjusted life years]".

The CDC's forthcoming recommendations re neonatal circumcision are in the news at the moment (see, for example, Debate on circumcision heightened as CDC evaluates surgery [Washington Post, 19 Jan]), and of course there is much speculation about what those recommendations will be. To my mind, there's an interesting clue in the conclusions of this paper:

Racial and ethnic groups who could benefit the most from circumcision may have least access to it due to insurance coverage and state Medicaid policies, and these financial barriers should be addressed. More data on the long-term protective effect of circumcision on heterosexual males as well as on its efficacy in preventing HIV among MSM would be useful.

(Emphasis added.)