The EpiGEH device monitors waterborne acute gastroenteritis (AGE) epidemics. It crosses data from the National Health Insurance Data System (SNDS) with the map of drinking water distribution units (UDI) in France to identify AGE epidemics potentially linked to water contamination tap. Contamination of distributed water can, in certain cases, occur following heavy precipitation which leads to runoff which may be accompanied by an increase in the load of pathogenic agents in the raw water. The objective of this study was to propose a methodology for constructing and evaluating a rainfall indicator and alarm predictive of an epidemic risk based on data from waterborne epidemics investigated; and on this basis to identify among the signals of the EpiGEH device, those for which the influence of rain was plausible. Data from 30 waterborne AGE epidemics confirmed by a field investigation and occurring between 2010 and 2021 were used to select the rainfall indicator and calibrate the rainfall alarm. On these epidemics, the influence of rain was considered plausible (positive alarm) when the estimated rainfall indicator exceeded the 4th quintile of monthly rainfall. The rainfall indicator was then applied to the 9,510 signals from the EpiGEH system recorded between 2010 and 2021. The rainfall alert conditions were met for 3.5% of the signals (n=312) with a delay between the start of the rains and the first cases (period of exposure to rain) of fifteen days (respectively 9.3% of signals (n=837) with a delay of 21 days). The Provence-Alpes-Côte d’Azur, Corsica, Occitanie and Auvergne-Rhône-Alpes regions were those for which the proportion of signals associated with a positive rainfall alarm was the highest (from 11.0% to 14.5%) .For the signals affected by a positive alarm, the average time between exceeding the rainfall reference threshold and the appearance of the first cases of GEA in the detected epidemic was 5.4 days. The main added value of these analyzes lies in the possibility of identifying among the signals detected by the EpiGEH device, those for which the vulnerability of drinking water production systems to precipitation played a determining role. The corresponding water distribution units should be prioritized to strengthen their resilience to adverse weather conditions, in order to better secure against epidemic risk. More in-depth studies integrating land type and land use data would be necessary to refine the link between rainfall and the risk of occurrence of water-borne AGE epidemics.
Auteur : Pouey Jerome, Mouly Damien
Year of publication: 2024
Collection : Studies and surveys
