Summary

Epidemiological studies have shown that if people are HIV-negative, having one or more of a number of other common sexually transmitted infections (STIs) considerably increases their risk of becoming infected with HIV.

The same is true in reverse of HIV-positive people: being co-infected with one or more other STIs considerably increases their chances of transmitting HIV, in some cases even if they are on fully suppressive antiretroviral therapy.^1,2

Various studies have found mechanisms behind these increased risks. Therefore, it makes sense to consider whether treating STIs, whether on an individual, targeted, or mass-population level, would reduce HIV incidence or HIV infectiousness amongst those individuals/populations.

A number of small studies have reported some success with this approach. However, only one of the handful of randomised controlled trials (RCTs) that have evaluated STI treatment as an HIV-prevention measure has produced a positive result. All others have failed to make a significant difference. This may be due to the stage of the epidemic reached, to other aspects of trial design (such as the provision of condoms) and to infection patterns in the trial populations (see more below).

STIs encompass a wide variety of different infections, some bacterial and others viral. While most are curable or self-limiting, others, such as herpes, are chronic, lifelong infections, such as HIV. Treatment regimens and RCTs of them are rather different and are dealt with in different sections below.