Taken alongside these last two studies, the increases in STIs in the other studies which, by themselves, were not statistically significant, added up to a consistent trend that was significant. This is a good example of how meta-analysis can add power to a finding.
This study shows several things. It shows that, averaged across all the studies, starting PrEP has been accompanied by a statistically significant increase in STI diagnoses. It shows that this increase is greater in rectal STIs. It shows that the increase in STIs has become more pronounced in the last couple of years.
It also shows that in many of the studies, starting PrEP has also been accompanied by increases in what should perhaps now be called STI risk behaviour – given that the increases in STIs are accompanied by falls in HIV infection.
The researchers say that the data seem to show increases in
the number of partners and/or the number of occasions in which condoms are not
used, rather than the proportion of men who don’t use condoms. In other words,
PrEP does not seem to be associated with a sudden abandonment of condoms, or in
men who always use them stopping use. However, men who are already inconsistent
condom users seem to be increasingly willing to take a chance on not using them.
This is what would be expected if PrEP is preferentially used by those already
at the highest risk of HIV.
The researchers comment that they could not establish the degree of correlation between starting PrEP and increasing ‘risk behaviour’ given that the measures of risk behaviour are so varied and are somewhat out of date. No study, for instance, asked about the actual or perceived viral loads of HIV-positive partners, and none asked specifically about group sex, though PROUD did subdivide risk by number of partners.
They also comment that it is now more important to chart how risk of both STIs and of HIV changes over time in individuals, as they move in and out of ‘seasons of risk’, rather than to document average behaviour over cohorts.
There is no evidence from this study that increases in STI testing may lead to more infections being treated and therefore an eventual fall in STIs. The STI increases were not associated with numbers of tests and therefore are more likely to reflect increased risk than increased diagnosis.
The authors conclude that “Responses to emerging trends in risk compensation need to be balanced against the considerable HIV transmission averted and the long-term prevention impact of greater PrEP coverage.”