On 27 September 2017, a local hospital reported to the Regional Health Agency (RHA) Auvergne-Rhône-Alpes, 5 suspected cases of leptospirosis. These cases (5 young men) took part in a canyoning weekend with a group of 26 persons in the Grenant River (Savoie, 73) during the second weekend of September. Four of them were hospitalized with fever, myalgia, arthralgia, thrombocytopenia and kidney, liver or neurological disorders. A multidisciplinary investigation team was set up in order to describe the outbreak, identify the likely source of infection and implement the necessary control measures.

The RHA asked canyoning clubs, laboratories, hospitals and general practitioners around the Grenant River to report possible cases to ensure all of them were identified. A possible case was a person of the group with symptoms compatible with leptospirosis between 9 September and 15 October 2017, and a confirmed case was a possible case with laboratory evidence (a biological test was proposed to each possible case). Each positive case was confirmed by the national reference center for leptospirosis (Institut Pasteur). A standardized questionnaire was used to interview each member of the group and collect demographic characteristics, clinical and biological information, recreational exposures during the whole weekend and information on individual protective measures used against leptospirosis. In the same time, environmental investigation was performed to explore potential infectious reservoirs and environmental conditions near to the canyoning site.

Twenty-three participants of the group answered to the questionnaire. Three were unreachable. Five confirmed cases of leptospirosis were identified, either by PCR or serology. For two cases, the species L. kishneri was identified by sequencing and Microscopic Agglutination Test (MAT) analysis detected the serogroup grippotyphosa. The only environmental risk exposure identified was canyoning in the Grenant river water. During the activity, all the participants wore a full body wetsuit. Only the absence of gloves could be notice. Two cases reported some skin lesions, but no significant wounds. Several members mentioned the presence of cows on the riverside, which are a possible reservoir of leptospira. No wild animals were seen around the canyoning site or near the camping where the participants were staying during the weekend. However, the river surroundings are known as hunting areas where hunters eviscerate wilds animals. A significant flow with muddy water was also described by all of them. Moreover, this weekend has been preceded by heavy rainfall after a long dry period and environmental investigation pointed out the spreading of manure on the edge of the river.

According to the results, the most appropriate hypothesis is a contamination by contact of water with mucous membranes during canyoning activity. We observed many favorable environmental conditions including significant rainfall, presence of cows and manure spreading near to the canyoning site. The formal identification of the contamination source was not possible, but it was reported that in this region, Grippotyphosa is the third serogroup responsible for bovine leptospirosis. The RHA immediately suspended the canyoning activities in the Grenant until the end of the season. This request has also been related by social and professional networks. In addition, health professionals and all canyoning sites were informed about the outbreak, leptospirosis risk and individual prevention measures. We recommend to check compliance with the regulations on manure spreading, improve the application of preventive measures to practice fresh water sport, raise awareness about importance and benefit of a rapid medical consultation in case of symptoms, and recommend to health professionals in the region an active surveillance of cases to rapidly identify areas of transmission.