Bridge populations in the spread of HIV/AIDS in Thailand

Objective: To determine the extent to which men provide a bridge population between, commercial sex workers (CSW) and the general female population in Thailand. Design: Sexual network and serological data were collected from a systematic quota sample of low income men and truckers during 1992 in three Thailand provinces. Completed sample size was 1075 men aged 17-45 years and 330 truckers. Methods: Sexual network information was used to identify those men who have sex with both female CSW and non-CSW partners (the 'bridge population'). A new method was used for calculating the partner acquisition rate and to establish the potential number of women exposed to HIV via inconsistent condom use among the bridge population. Results: Approximately 17% of men and 25% of truckers can be included in the bridge population. These men are more likely to be HIV-positive and to have had at least one other sexually transmitted infection in the past year (odds ratio, 2.2 and 3.4, respectively). Consistent condom use with CSW is less than 30%, and is less than 1% with non-CSW partners. As a result, 30 women in the general population were potentially exposed to HIV per 100 sexually active men in the last year: nine women each additional year. Younger men and truckers expose almost twice as many women to HIV; more female peers than wives are exposed. Conclusion: Bridge populations may be as important as 'core groups' for the spread of HIV into the general Thai population. Young men and women are strategic intervention targets because they have more partners, are more likely to be in bridging networks, and are more receptive to condom use.