Shifts in condom use following microbicide introduction: should we be concerned?

OBJECTIVES Abandoning condoms for microbicides is termed 'condom migration'. This study estimated the reduction in condom use that can be tolerated following the introduction of an HIV- and sexually transmitted disease (STD)-efficacious microbicide without increasing an individual's risk of HIV infection, and explored how microbicide use affects HIV-risk. DESIGN Development of a static mathematical model to compare how different combinations of condom and microbicide use affect individual risk of HIV and STD infection at a particular point in time. METHODS The model is used to identify the 'break-even point' at which any increased risk associated with condom migration is counter-balanced by the protection afforded with microbicides. Data from Benin is used as a case-example. RESULTS Considering a 50% HIV- and STD-efficacious microbicide, groups that use condoms with 25% consistency or less could cease using condoms without increasing their risk if they use microbicides in 50% or more of sex acts. However, migration may increase risk if the initial condom-consistency is high (> 70%) and microbicide-consistency is low (< 50% of non-condom-protected acts). For the Benin case-example, if condoms are initially used in 70% or less of sex acts, and if consistency of condom use is sustained following microbicide introduction, there will be a 20% or greater reduction in HIV-risk if the microbicide is used in 50% of non-condom-protected sex acts. CONCLUSIONS There are likely to be many situations in which the benefits of microbicide use outweigh the negative impact of condom migration, and where microbicides could substantially reduce HIV-risk.