National cartography of water points for the presence of Vibrio spp. in Belgium

Introduction: Most Vibrio spp. are environmental and non-pathogenic, but they can also cause illnesses such as wound infections and gastroenteritis. Invasive clinical cases of vibriosis have also been described in Belgium after water contact (De Keukeleire et al., 2018). These recent years, an universal increase occurred in the number of reports of human infections involving non-O1, non-O139 V. cholerae and other Vibrio spp. Waters for recreational use such as lakes and sea water are not yet monitored for Vibrio spp. That is why the Belgian national reference center conducted a study, by doing a cartography of Belgian water points for the presence of Vibrio spp. to evaluate its possible impact on public health.

Methods:

Sampling of waters was performed monthly between May and September 2021. These were done in different areas in Wallonia (Butchenbach, Robertville, Warfaaz lakes) and in Flanders (Blaarmeersen, Donk, Donkvijver, Boerenkreek lakes) including samplings in the North Sea (Knokke). The temperature and pH of the water were systematically recorded. The collected water was then filtrated, cultured and the “most probable number” method was used for bacterial quantification. The growing colonies were identified by Maldi-Tof and multiplex PCR.
Results:
No Vibrio spp. was found in the screened water points in Wallonia. However, several Vibrio spp. (Non -O1, Non-O139 Vibrio cholerae, Vibrio alginolyticus and Vibrio parahaemolyticus) were isolated at notable concentrations from different water points of Flanders (Blaarmeersen, Donkvijverand and Boerencreek) and from the North Sea. The monthly calculated concentration of Vibrio spp. was correlated with an increase of the water temperature as in June (22°C) the Vibrio cholerae concentration was evaluated at 110 CFU/ml while in August (24.2°C), the concentration reached >11000 CFU /ml. No impact of the pH was observed.
Conclusion:
Our study demonstrate the presence of Vibrio spp. at concentrations able to cause human infections in different water points mostly in the North of Belgium. This study supports the recommendation to include Vibrio spp. in water quality controls in order to define if water recreational activities are harmless for humans in Belgium.