Background Districts in north Karnataka have the highest HIV prevalence and female sex worker (FSW) to male population ratio in India. We examined the variability in socio-cultural, behavioural and clinical determinants contributing to HIV and syphilis prevalence in two neighbouring north Karnataka districts.

Methods FSW recruited from targeted intervention clinics responded to an oral questionnaire, underwent clinical examination and provided a blood sample for HIV and syphilis testing. We conducted univariate and multivariate logistic regression with HIV and syphilis as outcomes and with age, place of residence, marital status, literacy, monthly income, alcohol use, age at sexual debut and commercial sex work, clientele over the past week and STI syndromes as variables.

Results 1545 and 1551 FSW were recruited in the two districts. HIV (8% vs 6%) and syphilis prevalence (3% vs 1%) was significantly higher in district A. District A had significantly higher proportions of rural residents (92% vs 81%), devadasi (67% vs 15%), illiteracy (80% vs 64%), higher income (Rs6000 vs Rs5000), clientele per week (6 vs 4) and STI syndromes (16% vs 7%). While age at sexual debut was similar in both districts, significantly higher proportion in district A initiated sex work below the age of 15 (26% vs 11%). Alcohol consumption was higher in B (15% vs 3%). The odds of being HIV positive was significantly higher amongst FSWs with income > Rs5000 per month (AOR 1.61), being devadasi (AOR 2.43), consuming alcohol (AOR 1.64), h/o STI syndrome in the past 6 months (AOR 1.97) or clinically with an STI (1.95).

Conclusion Despite being neighbouring districts with similar socio-demographic backgrounds, significant variability in the prevalence of HIV and syphilis is perhaps contributed by the variability in prevalence of specific socio-cultural factors, behaviours and clinical syndromes of STI.