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BACKGROUND: An outbreak of gastroenteritis occurred in August 2013 and affected at least 19 individuals associated with a Japanese-style restaurant (Restaurant X) in Springfield, Missouri.
METHODS: An epidemiological, microbiological and environmental investigation was conducted. A total of 33 people were interviewed to determine the extent of the gastroenteritis outbreak at Restaurant X. Of those 33 interviewed, 19 experienced symptoms indicative of norovirus and 8 of those were confirmed with norovirus genogroup 2, type 4, Sydney (GII.4.Sydney). An environmental inspection of the restaurant was performed to identify any food and/or environmental hazards that may lead to the spread of disease.
RESULTS: The suspect event leading to disease exposure occurred at approximately 6:30 pm on Saturday, August 17, 2013 at Restaurant X. The suspect index case was seated at a table in the back of the restaurant. During dinner, she became ill and vomited on the way into the bathroom. A busboy used a towel to clean up the dining room/lobby area that was contaminated with vomit. The restaurant was unable to identify the index case, which prevented epidemiology staff from interviewing or obtaining stool specimens for testing. Of the 19 symptomatic individuals (8 patrons and 11 employees) interviewed, nausea was the most common symptom reported (100%), followed by vomiting (94%), diarrhea (89%), and fever (22%). The average incubation period for individuals reporting illness was 25 hours and the average duration of symptoms was 29 hours. Disease onset dates ranged from August 18th through the 20th for patron groups and August 19th through the 23rd for employees. Analysis of employee assignments and customer locations on a floor plan of Restaurant X, demonstrated a correlation between illness and proximity to the vomiting incident. Investigators failed to identify a probable food source for disease transmission further supporting the hypothesis of environmental transmission.
CONCLUSIONS: While person-to-person spread is the primary mode of disease transmission for norovirus, there is convincing evidence that aerosolization of the virus via vomiting or diarrhea plays a significant role in the spread of disease. With this in mind, the most likely source of disease spread in Restaurant X was environmental contamination due to a vomiting incident that occurred in the dining room area on August 17, 2013. This hypothesis is supported by a review of the restaurant floor plan in addition to the average incubation periods and disease onset dates for patrons of Restaurant X.