Objective: Mobile populations are thought to be at high risk for HIV-1 infection. This study aims to determine the prevalence of HIV-1 infection, HIV-1 subtypes and socio-demographic and behavioural risk factors among fishermen in the Gulf of Thailand and the Andaman Sea.
Methods: A cross-sectional survey, consisting of face-to-face interviews and the collection of oral fluid samples, was conducted in Samut Sakorn, Ranong, Songkhla and Traat Provinces, Thailand, between January and April 1998. Oral fluid samples were double-tested for HIV-1 antibody by IgG antibody capture enzyme-linked immunosorbent assay and enzyme immunoassay, and confirmed by Western blot. The presence of subtypes B' and E was assessed using a peptide enzyme immunoassay.
Results: Of the 818 fishermen (582 Thai, 137 Burmese, 99 Khmer) 15.5% were HIV-1 positive: 14.6% among Thai, 16.1% among Burmese and 20.2% among Khmer. Of the 119 HIV-1 positive samples available for subtyping, 72 (61%) were subtype E, 15 (13%) were subtype B'; the subtype could not be determined for 32 (27%) samples. Sixteen per cent of subjects had ever visited a commercial sex worker outside Thailand. This behaviour was more prevalent among Khmer (40%) than among Thai and Burmese (12%). In univariate logistic regression analysis, being 25 to 32 years of age, compared with being older or younger; working as a fisherman between 4 and 10 years, compared with working for a shorter or longer period; being unmarried; being a steersman or mechanic, compared with being a skipper or ship hand; greater number of visits to commercial sex workers; having visited a commercial sex worker outside Thailand; alcohol or drug use before or during sex; being tattooed; and having a history of sexually transmitted disease were significantly related to prevalent HIV-1 infection. Male-to-male sex and injection drug use were rarely reported in this population. In multivariate analysis, being 25 to 32 years of age, being unmarried, having a tattoo and a greater number of visits to commercial sex workers remained in the model to predict HIV-1 prevalence. A history of drug injection was predictive for infection with HIV-1 subtype B'.
Conclusions: These findings indicate a high HIV-1 prevalence among fishermen in the Gulf of Thailand and the Andaman Sea. Risk factor analysis suggests that heterosexual intercourse is the major mode of transmission in this population. Increased efforts to reduce the spread of HIV-1 among this epidemiologically important group are urgently needed.