Norovirus strikes hundreds at obstacle race in France

In June 2015, near Nice in the Alpes-Maritimes department, an acute gastroenteritis (AG) outbreak occurred among participants of an obstacle race. An investigation in 2 phases was conducted to identify the source of infection and document the extent of the outbreak.

tough_mudder_16-340x227During phase 1, a message on Facebook asked the racers to report by email any symptoms. In phase 2, a retrospective study was conducted through an interactive questionnaire for all participants. Cross-sectional descriptive studies were conducted, completed by an analytical study of the potential risks factors. Microbiological and environmental investigations were conducted in order to identify the responsible agent. An analysis of antidiarrhoeal drugs reimbursements was conducted with data from the French national health insurance to confirm the epidemiological investigation.

During phase 1, on 8229 registered participants, at least 1001 adults reported an AG, which was resolved in 48H.

In phase 2, the risks factors of AG identified were due to: younger participants, first hour of departure time and ingestion of mud. Twenty stool specimens traced were negative for bacteriological research. Only 4 stool specimens were sent to the CNR of enteric viruses. They were all positive for Norovirus genogroup1 and genotype 2 (GI.2), strain of human origin.

Indicator bacteria were negative in the drinking water and positive in the muddy water. Outbreak origin was due to human transmission: a norovirus possibly introduced by stools or vomiting from one or more persons infected, transmitted through contaminated muddy water.

For the future, recommendations for the organisation of such events should be proposed. The risks related to these races should be assessed to guide health authorities and to guide organizers in their awareness of potential risks factors.

Investigation of an outbreak of acute gastroenteritis among participants of an Obstacle Adventure Race Alpes-Maritimes

S Giron, C Six