Objectives: To estimate HIV and sexually transmitted infection (STI) prevalence within the general population of Mysore district, and to examine differences in the distribution of risk factors associated with HIV prevalence stratified by sex.

Methods: A community-based study was conducted in Mysore, Karnataka state, southern India, between October 2005 and November 2006; final sample size 4653. A face-to-face interview was conducted, and blood and urine specimens collected to measure HIV and STI prevalences. Risk factors for HIV among men and women were examined using weighted and clustered logistic regression.

Results: Weighted HIV prevalence was 0.8% [95% confidence interval (CI) 0.52-1.09] overall and 0.7% (0.35-1.08) and 0.9% (0.51-1.37) in rural and urban populations, respectively. The prevalence of syphilis, gonorrhoea and chlamydial infection was 2.8% for men and 1.8% for women. In multivariate analysis, higher HIV prevalence was associated with ever having used a condom [odds ratio (OR) 2.75, 95% CI 1.01-7.47] and number of lifetime partners for men (OR 6.9, 95% CI 2.18-21.91). For women, HIV infection was associated with condom use at last sexual intercourse (OR 10.51, 95% CI 2.05-53.79), number of lifetime partners and reporting 'don't know' for whether ever had anal sex (OR 9.10, 95% CI 1.14-72.34).

Conclusions: HIV prevalence in the general population of Mysore was found to be comparable to recent prevalence estimates for Karnataka state, and also similar to recent prevalence estimates from antenatal clinic attenders for the district. Few modifiable risk factors for HIV infection were identified. There is evidence from this study that high-risk behaviour may have been underreported, but the prevalence of STI was generally low.