Hepatitis A outbreak: A threat of untreated tap water in school, Sungai Kolok District, Narathiwat Province, Thailand

Abstract

On November 12, 2023, a cluster of hepatitis A (HAV) infected students and personnel in a primary school in Sungai Kolok District was notified. We investigated the causes of the outbreak and risk factors to establish and implement control measures. Both retrospective cohort, descriptive and analytical epidemiological studies including environmental investigation were conducted. Active case finding was performed. A case was defined as a person in the school who has at least two symptoms of jaundice, fever, dark urine, loss of appetite, fatigue, nausea or vomiting, abdominal pain, dyspepsia, epigastric pain, and right subcostal pain between June 1, 2023 and April 5, 2024. Stool samples were tested for hepatitis A virus genetic materials and HAV genotype, while serum samples were tested for anti-HAV IgM. In addition, water supply, drinking water, and ice samples were tested for free chlorine, coliform bacteria, hepatitis A virus, and HAV genotype. We found 26 cases with illness onset occurring between July 29, 2023 and December 27, 2023, resulting in an overall attack rate of 15.2% (26/171). The affected individuals were aged 7 to 29 years (median 11 years). The water supply was from the untreated shallow well near the septic tank. No soap was provided and 94% of students and staff did not wash their hands after using the bathroom and before eating. Moreover, it was found that 69.6% abluted themselves using untreated tap water before praying and 21.1% swallowed it while rinsing their mouth. Laboratory results detected anti-HAV IgM and hepatitis A virus genotype IA in patients, which are consistent with the strain found in the water supply. Additionally, no free chlorine was present in the water supply, and coliform bacteria were detected in both the water supply and drinking water samples. Analytical studies did not identify statistically significant risk factors. Chlorine tablets, clean water, and soap were temporarily provided. Since establishing a permanent treated water supply in January 2024, no cases have been reported. The cause of the outbreak is likely from untreated water supply and poor hygiene. Improving water quality, sanitation, and hygiene is crucial for preventing future outbreaks.