The study is by the Desmond Tutu HIV Centre at the University of Cape Town. It found that 75% of men as opposed to 32% of women were able to predict when they were going to have sex. About a third of respondents said they had sex at least once a week. None of the study participants, 52% of whom were women with an average age of 28, said they had sex every day.
"Although these results are preliminary findings of a larger study, they're significant in the sense that they may indicate that intermittent pre-exposure prophylaxis will work better among men," said study author Professor Linda-Gail Bekker. "It also shows us that weekends are the periods when the most protection will be needed."
Intermittent pre-exposure prophylaxis is when an antiretroviral pill is taken a few days a week to prevent infection. Three large studies have found that a daily dose of Truvada, which contains two types of antiretrovirals (ARVs), can reduce a person's chances of contracting HIV by up to 75%. However, in many of the studies, some participants did not take their pills regularly, resulting in significantly lower levels of protection.
Bekker's study – which is part of a larger study being conducted in South Africa, Thailand and the United States – aims to establish what the most favoured and efficient intermittent dose of Truvada would be for HIV protection. "What people are asking is, can you get away with less dosing, because obviously that can reduce side effects and costs, and it might be more amenable because we are talking about healthy, uninfected individuals having to take a daily pill," said Bekker. "We only have efficacy data for daily pill use and all three studies showed that the closer individuals got to 100% daily use, the closer they got to 100% protection."
Some participants are given Truvada daily, some three times a week and another group only takes it before and after sex. "We're trying to see which of those groups of people finds it easier to adhere to, bearing in mind that if you do sexually driven dosing, you're going to need to know when you're going to have sex," said Bekker. "We're also trying to find out if a pill before and after sex provides sufficient drug levels for HIV protection but even in this setting there may need to be a lead in dosing period to get adequate levels in the blood."
Bekker emphasised that pre-exposure prophylaxis is not meant to be a lifelong treatment; it's rather a "seasonal" intervention. "It's much like using oral contraception – there are periods in your life when you need it and times that you don't."
One of the advantages of pre-exposure prophylaxis is that it is self-controlled; in other words, you are able to use it without having to get your partner's approval. In that context, should it be introduced on a large scale, it could be focused on risk groups that are particularly vulnerable to infection, such as gay and bisexual men, sex workers and women hoping to have a baby.
"Women trying to conceive will obviously have sex without condoms and men who have sex with men are more vulnerable to infection because of anal sex," Bekker said.
"Pre-exposure prophylaxis can also be lifesaving for someone in a discordant couple where one person is HIV-positive and not yet on HIV treatment," she said.