People with high viral load most likely to report sex that could pass on HIV

Half of those most likely to pass on HIV were not on treatment, despite guidelines

Keith Alcorn
Published: 18 December 2017

People with HIV who had high viral load were more likely to report vaginal or anal sex without a condom with a partner of unknown or different HIV status, a US study of people with detectable viral load has found.

Viral loads tended to be lower among those people with a detectable viral load who reported always using condoms, or who reported condomless sex only with other people with HIV.

The findings are published in the journal Sexually Transmitted Infections by a research team led by Dr Michael Stirratt of the Division of AIDS Research at the US National Institute of Mental Health.

The study looked at people who have a viral load above 1500 copies/ml. Research shows that undetectable viral load (below 50 copies/ml) eliminates the risk of HIV transmission; a large study in Uganda found no cases of HIV transmission from people with viral loads below 1500 copies/ml. Understanding sexual behaviour among people in HIV care with viral loads above 1500 copies/ml is therefore important if healthcare providers are to manage patients with a detectable viral load.

The researchers note that around one-third of people living with diagnosed HIV who were followed over a two-year period in a study of more than 250,000 people living with HIV in the United States had a detectable viral load above 1500 copies/ml. Furthermore, that study found that the period of detectable viral load above 1500 copies/ml lasted for an average of 316 days.

The researchers identified people with detectable viral load at six university-affiliated hospitals in the United States as part of an intervention study designed to improve control of viral load and to improve retention in HIV care. During the study, participants were asked to fill out an online interview about their sexual behaviour during the previous two months, with the assurance that the results would be completely anonymised and would not form part of their medical record.

Participants were asked if they had had anal or vaginal sex in the previous two months, and if they had had anal or vaginal sex without a condom. Participants who answered 'yes' had to specify whether condomless sex was with “someone you knew was HIV-positive” or “with someone who was HIV-negative or whose HIV status you didn’t know”.

The study enrolled 1315 people with viral loads above 1500 copies/ml, 61% of whom were taking antiretroviral treatment. The sample was 38% men who have sex with men, 32% heterosexual men and 30% women. Sixty-two per cent of the participants were black, 18% white, 18% Hispanic and 2% other.

Just over one-third of the sample reported anal or vaginal sex in the past two months (37%) and 60% reported that they always used a condom. Just under 30% reported that they only had condomless sex with other people living with HIV, and only 14% reported condomless sex with partners of unknown or different HIV status. This group comprised 68 people, of whom 43 had viral loads above 10,000 copies/ml. Twenty-one of those had viral loads above 50,000 copies/ml (very high).

Serosorting and condomless sex with partners of different or unknown HIV status were each reported more frequently by men who have sex with men, but the researchers found no difference in sexual risk behaviour according to whether the viral load was in the range of 1500 copies/ml to 10,000 copies/ml, or higher. Condomless sex with partners of different or unknown HIV status, and serosorting, were less common in people taking antiretroviral therapy, although this trend was not found to be statistically significant in a multivariate analysis which adjusted for factors such as race, risk category and viral load level.

The authors caution that they cannot estimate the viral load at the time of sexual activity, but they do know that all participants had a viral load measurement above 1500 copies/ml no more than four months prior to the interview, and 90% of samples tested were obtained no more than two months before the study interview.

They also note that because they did not interview people with viral loads below 1500 copies/ml – including those with undetectable viral loads – they cannot say to what extent their findings reflect wider patterns of sexual behaviour, especially among men who have sex with men. Nor do they know how many sexual partners their interviewees had, whether those of different HIV status were using pre-exposure prophylaxis (PrEP), or how frequently condomless sex took place with partners of different HIV status.

The authors emphasise that only a small proportion of people with detectable viral load reported sexual behaviour with the potential to transmit HIV, but these individuals tended to have especially high viral loads. The authors say that among those on treatment, poor medication adherence and over-reporting of medication adherence are the most likely explanations for high viral loads. Nevertheless, the study also found that 39% of all people who qualified for the study did so because they were not taking antiretroviral treatment at the time of the study (2014-2015) when treatment was already recommended for all US patients with HIV. Half of all people reporting condomless sex with partners of unknown or different HIV status were not taking antiretroviral therapy.

“Directing interventions to patients in care with high viral loads and concurrent sexual transmission risk behaviours could strengthen HIV prevention,” the authors conclude.


Stirratt MJ et al. Characterising HIV transmission risk among US patients with HIV in care: a cross-sectional study of sexual risk behaviour among individuals with viral load above 1500 copies/ml. Sex Transm Infect, published online first, 2 November 2017, doi:10.1136/sextrans-2017-053178

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