The role of disease-specific infectivity and number of disease exposures on long-term effectiveness of the latex condom.

BACKGROUND Condom use is a primary prevention strategy for sexually transmitted infections (STIs). Consistent condom use substantially reduces the risk of HIV infection. Similar levels of effectiveness for reducing the risk of other STIs have not been established. Differences in disease-specific infectivity and the number of exposures to an infected partner may explain differences in condom effectiveness. GOAL The goal was to examine the impact of differing infectivities and increasing numbers of exposures on theoretical condom effectiveness. STUDY DESIGN Mathematical modeling using estimated disease-specific infectivities and condom failure rates. RESULTS Condom effectiveness decreases as disease-specific infectivity and the number of exposures to infection risk increase. CONCLUSIONS Condom effectiveness for decreasing STI risk is influenced by disease infectivity and the number of exposures. Generalizations from studies of relatively uninfectious STIs to highly infectious STIs or from short-term studies to longer-term situations will overestimate condom effectiveness.