Northern Thailand has one of the highest rates of HIV-1 infection in Southeast Asia. It is also home to a large number of Burmese migrants, believed to be at high risk of HIV. Our 1999 survey of 429 Burmese migrant workers of Shan ethnic origin in Chiang Mai province found a 4.9% rate of HIV-1 prevalence (5.7% men, 3.8% women). This figure is almost double that of comparable population groups in Chiang Mai, e.g. pregnant women and military recruits. HIV prevention programmes are urgently needed for this vulnerable population.
Currently, the northern region of Thailand has the highest prevalence of HIV-1 in the country . Prevalence in the early 1990s was reported to be as high as 57% among female sex workers (FSW), 40% among male patients at sexually transmitted disease clinics, and 10% among pregnant women . Burma (Myanmar) has also reported high rates (11%) among pregnant women in areas of Shan State bordering northern Thailand, and among injection drug users – 74% in Rangoon, 84% in Mandalay, and 91% in Myitkyina [2,3]. Many migrant workers in Thailand, the majority of which are ethnic Shans, have legally and illegally crossed the border in pursuit of higher income jobs and a better standard of living . Little is known about these Burmese migrants, although they are assumed to have a higher risk of HIV-1 than the Thai general population . We conducted a cross-sectional survey of Burmese migrants in northern Thailand to estimate the prevalence of HIV-1 and to identify demographic and behavioural risk factors associated with HIV-1 infection in this population.
During June and July of 1999, we recruited 429 ethnic Shan migrant workers from their work sites in Chiang Mai province (the city of Chiang Mai and four surrounding districts of Sansai, Maetang, Hangdong, and Maerim). Study participants completed a standard questionnaire administered face-to-face by trained interviewers and provided oral fluids for HIV testing (Epitope Inc., Beaverton, OR, USA). Positive enzyme immunoassay test results (Vironostika HIV-1 Microelisa System, Organon, Oss, the Netherlands) were confirmed by Western blot (Orasure, Organon Teknika Corporation, Durham, NC, USA).
Table 1 shows the sample characteristics, HIV-1 prevalence rates, and factors associated with HIV-1 infection.
Our study of Burmese migrant workers in Chiang Mai showed an overall HIV-1 prevalence rate of 4.9% (5.7% among men and 3.8% among women). This is almost double the rates of infection found in comparable population groups in Chiang Mai province, e.g. 21-year-old male military recruits (2.3%) and pregnant women (2.1%) . These HIV-1 infection rates were also more than double those estimated by the UNAIDS/WHO for the general Thai (2.2%) and Burmese adult population (1.9%) . This finding confirms our hypothesis that Burmese migrant workers are at increased risk of HIV-1 infection. Earlier studies [5,7] among ethnic Shan hill tribe villagers in northern Thailand in 1994 and among ethnic Shan migrant workers attending public hospitals in northern Thailand in 1996 found HIV-1 prevalence rates of 8.75 and 3%, respectively. Although the designs of these studies and our study are markedly different, these data show HIV-1 infection to be common among ethnic Shan.
We found that married workers in our study who live with a spouse had a higher risk of HIV-1 infection than those who lived alone; i.e. being single appears to be protective against HIV-1 infection. This finding contrasts with the assumption that single adults are at higher risk of HIV-1 and sexually transmitted disease infection. Being married is possibly associated with being older, and thus marriage may be a surrogate for the duration of exposure. Alternatively, those who are married may be more likely to visit FSW or intersects with some cultural behaviours of which we are unaware.
Visiting FSW has been shown to be a leading risk factor for HIV-1 infection in many parts of the world where HIV-1 is endemic. In one survey of male conscripts in northern Thailand , those who had sex with FSW were more than twice as likely to become HIV-1 infected than those who did not. A study of ethnic minorities in northern Thailand  also found an association between a history of sex with an FSW and HIV-1 infection among men. Although not statistically significant, we found an infection rate more than twofold higher among men who had ever visited an FSW compared with those who had not.
Our data also showed a higher risk of HIV-1 infection among workers employed in industrial settings than those with higher incomes. This finding may be explained by the fact that industrial sites and entertainment services usually concentrate in or near the city centre. Working in these urban areas may have exposed our study participants to an environment conducive to high-risk activities such as frequenting FSW. Their higher incomes may have provided them with the financial means to participate in such activities.
The Royal Thai Government has been trying to stem the influx of Burmese migrants into Thailand. One of the concerns raised is the risk of HIV-1 transmission from Burmese migrant workers to the general Thai population. Our study shows that Burmese migrants who arrived recently appeared to be less likely to be HIV-1 infected than those who arrived at an earlier date. The association between the duration of stay in Thailand (as a proxy for exposure to the Thai HIV-1 epidemic) and the risk of HIV-1 infection suggests that the transmission of HIV-1 between Burmese migrants and Thai nationals is bidirectional. Currently, little collaboration exists between Thai and Burmese health officials to prevent the spread of HIV-1 between the two countries . More bilateral cooperation must be sought to minimize the cross-border risk of HIV-1 infection among Burmese migrants.
The fear of deportation or other undesirable consequences of contact with authorities may have affected the representativeness of our study population and thus the reliability of our data. Nevertheless, our study is one of the first attempts to understand the transmission of HIV infection among Burmese migrants in northern Thailand. More research is needed to validate our study findings.
Thailand's vigorous HIV-1 prevention efforts have been praised for their success in stabilizing the HIV-1 epidemic. These efforts have, however, mostly focused on the general Thai population [9–14]. As our data indicate, Burmese migrant workers are at increased risk of HIV-1 infection. Immediate actions to help this vulnerable population could markedly reduce the spread of HIV-1 both among Burmese migrant workers and Thai nationals.
Frits van Griensvenc,d
Esther S. Hudesb
Jeffrey S. Mandelb
The authors appreciate the helpful collaborations of Achara Thawitwaboonpol-Entz of the College of Population Studies; of Vilai Chinveschakitvanich of the Institute of Health Research, Chulalongkorn University, Bangkok, Thailand; of Dr Varda Soskolne, Department of Social Medicine, School of Public Health and Community Medicine, The Hebrew University, Jerusalem, Israel; of Ms Chanitra Watcharapin of Organon Teknika (Thailand); of Ms Nancy Young and Dr Timothy D. Mastro of the Thai MOPH-US CDC Collaboration, Nonthaburi, Thailand; for their help in conducting this study, and of the Migrant Assistance Program, Chiang Mai, Thailand, for providing Shan language educational materials.
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