Microbicides could increase HIV infections

Mathematical models predicting the effect of microbicides show that their effect on HIV incidence and prevalence could vary enormously, according to local conditions. In some cases their adoption could cause an increase in HIV infections. 

Marie-Claude Boily of Imperial College, London, speaking at a symposium on modelling at the Microbicides 2010 Conference in Pittsburgh, said that models predict some paradoxical effects. 

A microbicide may have much more effect in a low-prevalence area than a high-prevalence one; it might reduce HIV infections in people who don’t often use condoms while considerably increasing them in people who use them consistently; and a rectal microbicide, used only for the occasional episode of anal sex, could in some heterosexual populations have more effect than a vaginal microbicide used frequently.