Epidemiological studies

In HIV-positive people, the presence of herpes greatly increases their risk of passing HIV on to others.

A study of US gay men presented at the 2008 CROI Conference¹ found that when the HIV-positive partner had HSV-2 and his HIV-negative partner did not, it made HIV transmission 16 times more likely.

Researchers traced 43 recent sexual partners of a group of men being evaluated for possible acute (i.e. very recent) HIV infection. Phylogenetic analysis showed that 14 of the HIV-positive men had transmitted HIV to their partners, while 29 had not. Individuals who transmitted HIV were more likely to have a bacterial STI at the time of testing than ones who did not (50% versus 7%, p= <0.003). HSV-2 raised the likelihood of transmission, but only when the HIV-positive partner had HSV-2 and the recipient did not. In these circumstances, transmission was 16 times more likely. If both partners had HSV-2, transmission was no more likely than if neither had it, or if the recipient had it but the HIV-positive partner did not.

This study is one of the few that has directly demonstrated the link between herpes and HIV transmission. This is partly because many African studies that have linked genital ulcer disease (GUD) with HIV transmission have not specified whether genital ulcers were caused by herpes or some other organism. One widely cited study from Rakai found that the presence of GUD doubled to tripled the risk of HIV transmission, but could not say how much of the GUD was due to herpes.² The proportion of GUD caused by herpes may be increasing over time. In South Africa, surveys of gold miners³ have found that in 1986 chancroid was responsible for 53% of GUD and herpes for only 1.3%. By 1998, the proportion due to chancroid was down to 38% and the proportion due to herpes was up to 28% - and this only counts GUD where the source of infection could be isolated.