An Outbreak Investigation of Acute Viral Diarrhea in a Private Elementary School, Maenum Sub-district, Koh Samui District, Surat Thani, Thailand, 13 - 17 July 2015

Abstract

Background: On July 12th, 2015, Office of Disease Prevention and Control Region 11 Nakhon Si Thammarat received notification of acute diarrhea cluster among students in a private school, Maenum, subdistrict, Koh Samui, Surat Thani from a hospital. We started outbreak investigation during July 13th – 17th, 2015. The objectives aimed to confirmed diagnosis and outbreak, to know the magnitude of outbreak, to identify the source, etiology and risk factor of the outbreak and to give a recommendation for control and prevention measures.
Methods: Active case finding was conducted in the school. A case was defined as a person in this school who had loose stool at least 3 times or watery diarrhea at least 1 time in 24 hours with one of the following symptom; fever, abdominal pain or vomiting during June 1st – July 17th 2015. Analytic study was carried out by retrospective cohort study. We collected water and stool samples for identify enteropathogenic bacteria by culture and virus by molecular testing.
Results: Totally 41 cases were met case definition and overall attack rate was 19.11%. All cases were students. Median of age was 7 years with minimum 2.5 years and maximum 11 years. The highest specific attack rate by class was in grade 1 (43.33%) followed by grade 4 (35.00%) and grade 5 (26.32%). Majority of the cases developed fever (73.2%), followed by loose stool (65.9%) and abdominal pain (48.8%). The outbreak pattern was a mixed type of propagated source and common source. Contacting with ill person who had been vomiting or diarrhea and brushing at 2nd floor station were the significant and independent risk factors for this outbreak. The molecular testing in the stool samples were positive norovirus for 1 case and poisitive rotavirus for 1 case. Water and food handler’s finger swabs were positive Bacillus cereus (75.00%), Aeromonas caviae (25.00%), Aeromonas veronii biovar sobria (12.5%), Aeromonas hydrophila (12.5%) and brushing water at 2nd floor station was positive norovirus. In addition, residual chlorine levels in the water were below 0.1 ppm in all reservoir.
Discussions and Conclusions: The cause of this outbreak was compatible with virus particular norovirus and rotavirus. There was evidence of the virus contaminated in the water system. We suggested that, in immediate action the school must clean and disinfection in the water systems with hyperchlorination and for long term action, the school must rebuilt the water storage tank and move to on the ground. We educated the teacher how to disinfection of contaminated area and cloth by sodium hypochlorite.