Population Based Survey of the COVID-19 Outbreak in the Haut-Rhin Department from January to April 2020

Abstract

Background: The department of Haut-Rhin is identified as one of the first clusters of the COVID-19 outbreak in France. The alert was raised by local sanitary authorities on March 3rd, following a week of prayer organized by a Christian church which gathered about 2000 people from February 17th to 21th 2020 in Mulhouse, France and identified as the origin of the epidemic in Haut-Rhin. Our aim was to document the temporal distribution of the COVID-19 cases, to identify the beginning of the outbreak and to evaluate the potential role played by the Christian gathering on the virus propagation. Methods: We conducted an online population-based survey to evaluate if people had symptoms commonly experienced in case of COVID-19 infection and when. The reproduction number was approximated by the number of cases induced in one family. The generation interval was computed as the difference between the occurrence days of successive family cases. The epidemic threshold was estimated from the upper limit of the 95% confidence interval of the incidence moving mean on the last seven days, using December 15th 2019 to January 15th 2020 period as reference. Results: Preliminary results were obtained from data reported by 1244 families representing almost 3.300 individuals. Reproduction number is estimated to 1.4 and generation interval to 4 days. The curve of incidence shows that the epidemic begun before the sanitary alert was given and that some of the attendees to the Christian week of prayer displayed symptoms before the event. The curve of the seven days moving average shows a crossing of the epidemic threshold on January 27th, with a first wave until February 17th. The second wave, much more important, immediately followed with a maximum after mid-March. The epidemic then diminishes rapidly later in March, crossing again the epidemic threshold on April 6th. Discussion: Our results are preliminary and the survey is still ongoing. The epidemic in Haut-Rhin started five weeks before the sanitary alert and the Christian meeting played a secondary role. These results highlight the interest of coupling population-based surveillance to hospital disease surveillance to trigger an alarm earlier in case of emerging disease.