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.