Effect of condom-use measures in predicting sexually transmitted diseases: variation by individual and contextual factors of sexual risk.

Inconsistent findings in the global literature regarding the effectiveness of condom use against sexually transmitted diseases (STDs) may result from variations in the measurement of condom use. In this study, we assess the sensitivity and specificity of six condom-use measures in predicting STD infection, and assess the difference in sensitivity and specificity by type of sexual partner (clients versus stable partners), type of STD, ethnicity (Han versus non-Han), years of formal schooling (≤6 versus >6 years) and level of risk of STD exposure (high versus low). Cross-sectional data were obtained from 454 female sex workers (FSWs) in Guangxi, China. Measurements of condom use were created along types of use (any use, consistent use, correct use, or the combination of consistent and correct use) and periods of recall (life time, last month or recent three sexual episodes). Measures of consistent use had higher sensitivity and lower specificity than measures of any use in predicting STDs among FSWs, regardless of the recall period and type of sexual partner. Incorporating correct use improved the measures of consistent use. Measures of consistent use and the combination of consistent and correct use demonstrated high sensitivity in predicting particular STDs. They showed higher sensitivity in predicting STDs among FSWs who reported higher risk for STD exposure than among FSWs who reported lower risk of exposure to STDs. In conclusion, the findings suggest the superiority of consistent use and correct use of condoms in predicting STD infection. The findings also underscore the importance of considering the context of sexual risk such as type of sexual partner and risk of exposure to STD infection when we measure condom use. Future studies of condom effectiveness should collect and quantify these contextual and individual factors among the target population.