Norovirus outbreak in five schools of Nakorn Ratchasima Province, Thailand, 2016

Abstract

Backgrounds: On 24^th November 2016, Bureau of Epidemiology (BoE) received notification of 216 food poisoning cases in 5 schools in Nakorn Ratchasima province. BoE, Office of Disease prevention and control 9th region and Nakorn Ratchasima Provincial Health Office jointly conducted an investigation to identify the causative organism of the outbreak, to find the implicated food and water of the outbreak, to describe the contamination method and to identify the source of the outbreak.
Methods: Active case finding was done to find further cases in school. Rectal swab specimens were collected in acute gastroenteritis cases that still had symptoms. Retrospective cohort study was done in school with highest attack rate. Unmatched case-control study was performed in school that received food and water ingredients from more than one source. Environmental survey and specimens’ collection were done in schools and suspected potential sources of contamination.
Results: There were 518 acute gastroenteritis cases in school A, B, C, D and E with attack rates of 8.69%. Most cases consumed ice with water and presented with abdominal pain, nausea and vomiting. Laboratory results revealed positive Norovirus from polymerase chain reaction (PCR) in 6 of 17 specimens (35.29%). Retrospective cohort study was done in school D and revealed association between consuming ice with drinking water and occurrence of the outbreak, adjusted OR was 3.59 (95% CI 1.58–8.14). Ice factory A was suspected because 4 schools received ice from this factory. Unmatched case-control study was done in school A and revealed association between consuming ice from ice factory A and occurrence of the outbreak, adjusted OR was 3.35 (95% CI 1.58–7.10). Ice production pathway of ice factory A was a closed system. Laboratory result from ice specimen of ice factory A revealed positive for Vibrio cholerae non O1/non O139/non 141 without cholera toxin.
Conclusions: This was an acute gastroenteritis outbreak in multiple schools caused by Norovirus. Ice consumed with other drinks was associated with occurrence of the outbreak which presented mainly as upper gastrointestinal symptoms. Ice factory A was suspected as the source of the outbreak, however the method of contamination was unknown.