An outbreak investigation of Hepatitis A in 8 provinces along the upper gulf of Thailand, February–June 2017

Abstract

Background: In February 2017, Department of Disease Control was notified several cases of hepatitis A from two central provinces. After situation reviewed, we found hepatitis A outbreak in several provinces along the upper Gulf of Thailand. An outbreak investigation was conducted during February-June 2017 to identify the cause of the outbreak.
Methods: A descriptive study was conducted by reviewed medical records of patients diagnosed with Hepatitis and other diseases that may have similar symptoms during September 2016 -June 2017 in 8 provinces in the outbreak area. Matched case–control study was conducted. The case was a confirmed case with onset from 8 January to 20 February 2017. The control was a person who had age not differed from the cases than 5 years, stayed in a same village with the case and had negative anti-HAV IgM and IgG by ELISA. Environmental and laboratory studies were conducted, including collected water and foods samples in the epidemic area for HAV testing.
Results: Totally 191 cases were identified including 155 confirmed cases. The male to female ratio was 1.01:1. The median age was 25 years old, ranged 2-73 years old. The onset dates were from 27 September 2016 to 24 June 2017. Epidemic curve was similar to a common source outbreak. The case–control study showed pickled mussel consumption significantly increased the risk (adjusted odds ratio 2.35, 95% CI 1.07–5.16). Environmental studies found that the pickled mussel has potential contamination in several steps, from the shellfish farms to cleaning process at the pickle mussel factories. DNA sequencing of the cases showed similar patterns between provinces. Hepatitis A virus was identified from the intestine of pickled mussel that collected from the Maeklong Railway market, Samut Songkhram province.
Conclusions: This widespread and prolong hepatitis A outbreak in provinces along the upper Gulf of Thailand might associated with pickled mussels consumption. However, due to limitations in the investigation process, the specific source of contamination could not be identified. The interventions such as educated people, increased chlorine residue in tap water, and improved environmental sanitation in the area were implemented.