Previous studies of anti-HAV IgG prevalence in Thailand.

<p>Previous studies of anti-HAV IgG prevalence in Thailand.</p

Declining Trend of Hepatitis A Seroepidemiology in Association with Improved Public Health and Economic Status of Thailand

<div><p>Hepatitis A virus (HAV) is transmitted via the fecal-oral route from contaminated food or water. As part of the most recent survey of viral hepatitis burden in Thailand, we analyzed the current seroprevalence of HAV in the country and compared with data dating back to 1971. From March to October, 2014, a total of 4,260 individuals between one month and 71 years of age from different geographical regions (North = 961; Central = 1,125; Northeast = 1,109; South = 1,065) were screened for anti-HAV IgG antibody using an automated chemiluminescent microparticle immunoassay. Overall, 34.53% (1,471/4,260) possessed anti-HAV IgG antibody, and the age-standardized seroprevalence was 48.6%. Seroprevalence rates were 27.3% (North), 30.8% (Central), 33.8% (Northeast) and 45.8% (South) and were markedly lower than in the past studies especially among younger age groups. The overall trend showed an increase in the age by which 50% of the population were anti-HAV IgG antibody: 4.48 years (1971–1972), 6 (1976), 12.49 (1990), 36.02 (2004) and 42.03 (2014).This suggests that Thailand is transitioning from low to very low HAV endemicity. Lower prevalence of HAV correlated with improved healthcare system as measured by decreased infant mortality rate and improved national economy based on increased GDP per capita. The aging HAV immuno-naïve population may be rendered susceptible to potential HAV outbreaks similar to those in industrialized countries and may benefit from targeted vaccination of high-risk groups.</p></div

Correlation between infant mortality rate (per 1,000 live births), GDP, and age at which 50% of the population possessed anti-HAV antibody.

<p>Infant mortality rates (pink graphs), GDP per capita (blue graphs), and the mean age at 50% anti-HAV IgG positivity in the population (black line) are indicated. Half of the population around the mean age is denoted in gray areas.</p

The frequency of anti-HAV IgG positivity in each age group.

<p>Numbers above the line charts indicate the total seroprevalence for each age group.</p

Regions and demographics of individuals assessed for immunity to HAV.

<p>Regions and demographics of individuals assessed for immunity to HAV.</p

Total hepatitis A infection cases and morbidity rates in Thailand.

<p>Data available from 2003 to 2014 (excluding 2004) from the Bureau of Epidemiology, Thai Ministry of Public Health, are presented as line charts. Rates are indicated per 100,000 persons.</p

Map of Thailand and the domicile of study participants.

<p>Seven provinces from the four regions (North, violet; Northeast, green; Central, blue; and South, yellow) are shown. Districts within a given province are denoted in different colors depending on the population density (range 0 to ≥ 601 individuals/km²). Number of study participants from each district is indicated.</p

Comparison of anti-HAV IgG positivity from 1971 to 2014.

<p>Seroprevalence data from this and other studies were plotted as line charts. The dotted line denotes 50% anti-HAV IgG positivity. Intersection with the seroprevalence curve indicates the mean age at which 50% of the individuals in the population possessed anti-HAV IgG (denoted by the numbers on the line graphs) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0151304#pone.0151304.ref016" target="_blank">16</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0151304#pone.0151304.ref018" target="_blank">18</a>].</p

The Success of a Universal Hepatitis B Immunization Program as Part of Thailand’s EPI after 22 Years’ Implementation

<div><p>Hepatitis B vaccination for newborns was introduced in two provinces in 1988 as part of Thailand’s Expanded Program on Immunization (EPI), and extended to the whole country in 1992. Our previous studies showed that children and adolescents who were born after the implementation of this program had a carrier rate of less than 1%, compared with 5–6% before implementation. In 2014 we performed hepatitis B serosurveys among 5964 subjects in the different geographic regions of the country to evaluate the long-term immunogenicity and impact of universal hepatitis B vaccination in newborns as part of the 22-year EPI program, by assessing HBsAg, anti-HBc and anti-HBs seropositivity status. The number of HB virus (HBV) carriers, both children and young adults, who were born after universal HB vaccination was markedly reduced. The carrier rates among the age groups 6 months to 5 years, 5–10, 11–20, 21–30, 31–40, 41–50 and >50 years were respectively 0.1, 0.29, 0.69, 3.12, 3.78, 4.67 and 5.99%. The seropositivity rate for HBsAg in the post-EPI group was 0.6%, whereas in the pre-EPI group it was as high as 4.5% (<i>p</i><0.001). HBV infection by means of detectable anti-HBc had also drastically declined in the population born after the HB vaccine was integrated into the EPI program. We estimated that the total number of HBV carriers amounted to 2.22 million, or 3.48% of the total population, most of whom are adults. The HB vaccine is the first vaccine shown to be effective in preventing the occurrence of chronic liver disease and hepatocellular carcinoma. Universal vaccination campaign will contribute to the eventual eradication of HBV-associated disease.</p></div

Documented hepatitis A outbreaks in Thailand from 1984 to 2014.

<p>Circles denote outbreak events in different regions (North, purple; Central, blue; Northeast, green; South, yellow). Circle sizes correspond to the number of individuals affected. Outbreak in a calendar year is denoted as solid lines; those that continued to the following year are denoted in dashed lines. Line length corresponds to the recorded outbreak period.</p