To determine the prevalence of hepatitis B surface antigen (HBsAg) and antibody to hepatitis delta virus (anti-HDV) and associated factors among migrant sex workers in Chiangmai, Thailand. Methods: This cross-sectional study was conducted at various sexual entertainment venues in Chiangmai, Thailand, in 2019. Consenting participants were interviewed using a questionnaire, and plasma was tested for hepatitis B virus (HBV) markers (DiaSorin, Italy) and anti-HDV antibody (DIA.PRO Diagnostic Bioprobes, Italy), if HBsAg-positive. Associations between HBsAg positivity or HDV antibody and potential factors were examined using univariable and multivariable logistic regression analysis. Results: A total of 396 migrant sex workers, half of them female, were recruited between February and September 2019. Their median age was 25 years (interquartile range 22-30 years) and 95% were Burmese. Overall, HBsAg prevalence was 11.4%; 8.1% in females and 14.7% in males (Chi-square, p = 0.040). One-third were still susceptible to HBV. No HBsAg-positive participants had anti-HDV antibodies. HBsAg positivity was associated with being male (adjusted odds ratio (aOR) 3.01, 95% confidence interval (CI) 1.25-7.68, p = 0.014), having attended school (aOR 4.50, 95% CI 1.26-15.98, p = 0.020), being separated/ divorced/widowed (aOR 5.77, 95% CI 1.48-22.52, p = 0.012), and having unprotected sex (aOR 3.38, 95% CI 1.31-8.71, p = 0.012). Conclusions: In this young population, higher HBsAg prevalence in males may be related to sexual transmission, indicating the need for HBV screening programs linked with HBV prevention and care.

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Thailand has integrated Hepatitis B (HB) vaccine for newborns into the national Expanded Program on Immunization since 1992. The HB vaccination coverage was reported >96% in 2019 but the coverage among inhabitants of remote rural areas, particularly among hill-tribe children, remains unclear. This cross-sectional study aims to investigate the hepatitis B virus (HBV) seroprevalence among hill-tribe children living in 3 different areas in Omkoi District, Chiang Mai province, Thailand during September-November, 2018. Plasma samples were first tested for hepatitis B surface antigen (HBsAg). Sample negative for HBsAg were then tested for antibody to hepatitis B surface antigen (anti-HBs) levels and antibody to hepatitis B core antigen (anti-HBc). A total of 419 hill-tribe children were recruited, their median age was 11 years (interquartile range 9-12 years). Eighteen children (4.3%, 95%CI 2.6-6.7) were HBsAg positive. Among 401 remaining children, 269 had no HBV markers (67.1%, 95%CI 62.3-71.7), 91 (22.7%, 95%CI 18.7-27.1) were positive for anti-HBs only, 23 (5.7%, 95%CI 3.7-8.5) were positive for anti-HBc and anti-HBs, and 18 (4.5%, 95%CI 2.7-7.0) positive for anti-HBc only. The high prevalence of children susceptible to HBV infection and the high proportion of HBV infected children indicate that vaccination strategy needs to be improved in this rural area. Moreover, HBV serologic investigations are necessary in other rural areas to improve HB vaccination coverage. Keywords: Hepatitis B virus; Prevalence; Vaccination; Serological markers; Children; Thailand

Zika virus (ZIKV) epidemiological data in Thailand are limited. We assessed ZIKV IgG seroprevalence among young adults during 1997–2017 and determined factors associated with ZIKV IgG seropositivity. This retrospective laboratory study included randomly selected subjects aged 18–25 years participating in large clinical studies conducted in Thailand during 1997–2017. Stored plasma samples were analyzed for ZIKV IgG using an ELISA test (Anti-Zika Virus IgG, EUROIMMUN, Lübeck, Germany). Sociodemographic, clinical and laboratory data were used in univariable and multivariable analyses to identify factors associated with ZIKV IgG positivity. Of the 1648 subjects included, 1259 were pregnant women, 844 were living with HIV and 111 were living with HBV. ZIKV IgG seroprevalence was similar among the HIV-infected and -uninfected pregnant women (22.8% vs. 25.8%, p-value = 0.335) and was overall stable among the pregnant women, with a 25.2% prevalence. Factors independently associated with ZIKV IgG positivity included an age of 23–25 years as compared to 18–20 years, an HIV RNA load below 3.88 log10 copies/mL and birth in regions outside northern Thailand. Our study shows that a large proportion of the population in Thailand probably remains susceptible to ZIKV infection, which could be the ground for future outbreaks. Continued surveillance of ZIKV spread in Thailand is needed to inform public health policies.