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51% of New HIV Infections from Condom Failure During Anal Sex, Study Finds

, by Emily Land

Editor’s note: The following story reports the findings of a study which were derived using mathematical modeling. The findings reported here and in the study are not based on a clinical study of observed or documented transmission data. Mathematical modeling can be effective in making predictions about behavior, but readers should  approach these types of studies with a critical eye.

BETA Blog serves as a resource on new developments in HIV prevention, evolving approaches to HIV treatment, and strategies for living well with the virus. Stories about published research findings should not be interpreted as an endorsement by San Francisco AIDS Foundation of said findings. Our goal is to inform, empower, and inspire conversation.


A mathematical modeling study, published recently in PLOS One, provides insight into the role that condom failure or misuse is having on the HIV epidemic among men who have sex with men (MSM).  Of the 693 new HIV infections that occurred among MSM in Ontario in 2009, over half (51%) were estimated to have occurred during anal sex with a condom.

A team of Canadian researchers used HIV infection prevalence and incidence data for MSM in Ontario and a number of estimates for MSM not already infected with HIV including the number of total sex acts both oral or anal with HIV-positive partners; the probability of HIV transmission as a function of sex act; the preventive effect of antiretroviral therapy (ART); and an estimate of condom effectiveness. These parameters were then plugged into a mathematical model which was adjusted to fit the total number of yearly HIV infections.

From the over one million condom-protected episodes of anal sex that occurred between HIV-negative men and HIV-positive partners, researchers estimated 355 new HIV infections occurred. Whether or not HIV-positive partners were using ART also had an effect. A total of 341 infections occurred when HIV-positive partners were not on ART, whereas only 13 infections occurred when HIV-positive partners were.

The total number of anal sex episodes without condoms between HIV-negative men and HIV-positive partners was estimated to be much lower—around 100,000 (compared to the over one million condom-protected anal sex encounters). This lower frequency contributes to the smaller proportion of new infections (33%) that arose from unprotected anal sex.

The authors explain, “Though our results may seem surprising, they are actually quite intuitive. If condoms are used in a majority of sexual acts and condom effectiveness is less than 100%, it follows logically that a significant proportion of HIV infections would be due to condom failure.”

Over 1.3 million episodes of oral sex without a condom were estimated to have occurred between HIV-negative men and HIV-positive partners throughout the year. Although oral sex is known to be a lower-risk activity for HIV transmission, it was estimated to contribute 112 new infections during the year—a transmission rate of about 9 infections per 100,000 oral sex acts—accounting for 16% of new HIV infections that occurred among MSM in Ontario in 2009. This estimation includes instances when the HIV-positive partner was not on ART (with an associated transmission rate of about 16.5 per 100,000) and when the HIV-positive partner was on ART (with a much lower associated transmission rate of about 0.6 per 100,000).

“Although the risk of transmission in oral sex per act is low, those not on suppressive ART therapy may be 27 times more likely to transmit HIV,” explains Robert Palmer, one of the study’s lead researchers.

The researchers opted to err on the conservative side when they selected a measure of condom effectiveness, potentially overestimating how well condoms work. They note that the success rate used in their mathematical estimation (87.1%) is actually much higher than the estimate of condom effectiveness at preventing HIV transmission during anal sex specified by the U.S. Centers for Disease Control (67%). Implications of this difference may be that an even greater percentage of HIV infections are caused by condom failure—even higher than the 51% predicted by the current model.

Yet the authors are quick to caution against using their finding to deter condom use or publicize their ineffectiveness. Condom failure can be due to a number of factors, such as breakage, slippage, and “non-optimal use,” which can include delayed condom application so that the HIV-negative partner is exposed to virus in his partner’s pre-ejaculate.  Rather, the authors interpret their results as evidence that condoms “need to be used more effectively in this population, [so that] condom effectiveness can more closely approximate condom efficacy.”

They further explain that, “condoms have been and should remain an important tool in our armamentarium for reducing the risk of HIV transmission among MSM.”

These findings also hold implications for the important role that pre-exposure prophylaxis (PrEP) may play in further reducing infections that may occur when condoms fail. PrEP is a prevention strategy where HIV-negative individuals take antiretroviral medications to reduce risk of HIV infection.

“We are just now learning about the limitations of condom use. When condoms are used perfectly, they are protective against HIV and some other STIs. Yet, in practice, perfect condom use often does not occur.  PrEP is another very effective way to prevent HIV transmission. Adherence to PrEP has to be good, but not perfect.  And PrEP—unlike condoms—can be used anytime during the day as opposed to in the heat of the sexual moment,” explains Robert Grant, MD, MPH, of the Gladstone Institutes, the University of California at San Francisco, and San Francisco AIDS Foundation.

Selected Sources

Remis, R. and others. HIV transmission among men who have sex with men due to condom failure. PLOS One 9(9). September 11, 2014.


One Response to 51% of New HIV Infections from Condom Failure During Anal Sex, Study Finds

  1. Andrew says:

    I’m pretty surprised that this paper is being reported on so uncritically. A glance at the paper itself shows the inputs to the model are pretty dubious (to put it kindly). I think the headlines (and indeed the content of the paper) here have real potential to confuse and worry people needlessly. Rather than just repeating questionable conclusions you should be digging deeper into whether those conclusions are sound or not.