UNAIDS estimate that one infection will be avoided for every 5 to 15 men circumcised

In the high HIV prevalence countries of southern Africa, between five and fifteen men will need to be circumcised to prevent one HIV infection in the ten following years, at a cost of between $150 and $900 per infection prevented.

These are the conclusions of an expert review of mathematical models of the impact of male circumcision, organised by UNAIDS, WHO and the South African Centre for Epidemiological Analysis, and published in the open access journal PLoS Medicine.

The group also concluded that even if circumcised men either reduced their use of condoms or resumed sex too soon after the operation, circumcision would remain beneficial on a population level. They also concluded that women will indirectly benefit from circumcision.

Although there is compelling evidence from randomised controlled trials that male circumcision can reduce the risk of men acquiring HIV through heterosexual sex, the longer-term population-level impact of introducing or expanding male circumcision services remains uncertain. Questions have remained about the cost-effectiveness of male circumcision as an HIV prevention measure in the short, medium, and long term.

A number of different mathematical models have been developed to estimate the likely impact (and several have been previously described on aidsmap.com). However, the models have used different baseline assumptions and input variables, and so have sometimes produced slightly different results.

In order to come to a consensus about a number of key questions related to the impact of male circumcision, an expert group was convened to review the findings from six previous modelling studies.

Most of the models were based on assumptions from settings where at least 80% of men are not currently circumcised, where HIV is predominantly spread through heterosexual transmission and where HIV prevalence is greater than 15% of the general population. Prevalence is this high in southern African countries such as Zimbabwe, Zambia, Botswana, Namibia and South Africa, but not elsewhere in the continent.

The published paper does not contained detailed numerical projections of the impact of circumcision in various circumstances, and concentrates on the situation in the highest prevalence countries. The group used the modelling studies to come to a broad consensus on the answers to the key questions.

What is the expected impact on HIV incidence?

The models predict that, over ten years, one new HIV infection would be averted for every five to 15 men circumcised. In some circumstances, if almost all men are circumcised, HIV incidence could be reduced by around 30–50% in ten years.

In countries with a somewhat lower HIV incidence and prevalence, circumcision would have less impact. The group agreed that in such countries, circumcision programmes which focused on specific subpopulations could have a substantial impact. Such groups could be chosen on the basis of their low rates of circumcision or their higher HIV risk (men with HIV-positive partners; men with sexually transmitted infections; soldiers, truck drivers, migrant workers, etc).

What is the impact on women?

Circumcision does not directly benefit women, and if men resume sex too soon after being circumcised, women are actually at increased risk of HIV infection.

However the group concluded that women would benefit indirectly because their likelihood of meeting an HIV-positive male partner would decline. Moreover, reductions in sexually transmitted infections in both men and women would reduce women’s risk of acquiring HIV.

What is the impact of circumcising HIV-positive men?

Circumcision of an HIV-positive man does not reduce his risk of transmitting the virus. In fact, if a man with HIV resumes sex too soon after circumcision, incomplete healing could lead to an increased risk of HIV transmission. Two models addressed this issue, and concluded that this is unlikely to have an impact on a population level because the post-healing time is relatively short.

Moreover the group noted that systematic exclusion of men with HIV from circumcision might lead to stigma for all uncircumcised men. One model indicated that targeting circumcision to men with the highest risk of HIV exposure will provide the greatest overall benefit, even though this will also recruit more men with HIV infection.

What is the effect of risk compensation?

If men believe that circumcision protects them fully against infection, there is the possibility of an increase in sexual risk-taking. Three models suggested risk compensation by circumcised men and their partners would only have a “small effect” at the population level, unless it was to the extent of complete abandonment of condoms.

However, if increases in risk-taking took place across the entire adult population, this would substantially reduce the benefit of circumcision. The group recommend intensive communication campaigns to prevent this occurring.

Do the effects vary by age group of men circumcised?

The models showed that circumcising men who have not started sexual activity leads to the greatest population-level benefit in the long term, but circumcising 25 to 34-year olds has the biggest benefit in the first 20 years. Circumcising 50-year old men has little effect on HIV incidence.

The group did not find that circumcising new-born babies would be cost-effective. Although circumcision at this stage is safer and cheaper, the impact on HIV would not be seen for over 20 years.

How do the effects vary with speed of service scale-up?

The group concluded that rapid initial scale-up leads to a greater impact and is more cost-effective, with fewer circumcisions required to avert one infection, at a lower cost.

What are the discounted savings?

The models estimated that each infection that is prevented because of circumcision costs between $150 and $900, calculated over a ten-year time period. When calculated over twenty years, the cost per prevented infection is $100 to $400. Costs will be higher in lower prevalence countries.

These costs are based on $30-$60 per adult circumcision, and a life-time treatment cost of $7,000 per HIV infection (first-line therapy only).

Implementation

Findings from the modelling studies have been used to refine and validate a pragmatic, decision-makers' programme planning tool which can model what the scale-up of male circumcision may achieve and cost in specific settings.