Response to Foss et al., ‘Care should be taken when promoting microbicide use among sex workers who are able to use condoms consistently’

Abstract

Mathematical modeling analyses by ourselves and Foss et al. predicted that vaginal microbicides could substantially reduce the risk of HIV acquisition. Our analysis purposely considered a high-risk group of women namely female sex workers (FSW) in a high prevalence resource-constrained setting. We determined that increasing microbicide use would have a greater impact on reducing risk than increasing microbicide efficacy. We also quantified the break-even threshold for the level of condom replacement that could be tolerated given microbicide efficacy and usage so that the risk of HIV acquisition would not increase .We predicted that even if the microbicides that become available are low to moderately effective the probability that risk in FSW would increase (as a result of replacing condoms with microbicides) would be low. Furthermore in our threshold analysis we considered the worst-case scenario of complete condom replacement; if only partial condom replacement occurred results would be more optimistic. Our conclusions assume low-to-moderate condom use before the introduction of microbicides. (excerpt)