Cluster of COVID-19 in Northern France: A Retrospective Closed Cohort Study

Abstract

Background: The Oise department in France has been heavily affected by COVID-19 in early 2020. Methods: Between 30 March and 4 April 2020, we conducted a retrospective closed cohort study among pupils, their parents and siblings, as well as teachers and non-teaching staff of a high-school located in Oise. Participants completed a questionnaire that covered history of fever and/or respiratory symptoms since 13 January 2020 and had blood tested for the presence of anti-SARS-CoV-2 antibodies. The infection attack rate (IAR) was defined as the proportion of participants with confirmed SARS-CoV-2 infection based on antibody detection. Blood samples from two blood donor centres collected between 23 and 27 March 2020 in the Oise department were also tested for presence of anti-SARS-CoV-2 antibodies. Findings: Of the 661 participants (median age: 37 years), 171 participants had anti-SARS-CoV-2 antibodies. The overall IAR was 25.9% (95% confidence interval (CI) = 22.6-29.4), and the infection fatality rate was 0% (one-sided 97.5% CI = 0 - 2.1). Nine of the ten participants hospitalised since mid-January were in the infected group, giving a hospitalisation rate of 5.3% (95% CI = 2.4 –9.8). Anosmia and ageusia had high positive predictive values for SARS-CoV-2 infection (84.7% and 88.1%, respectively). Smokers had a lower IAR compared to non-smokers (7.2% versus 28.0%, P <0.001). The proportion of infected individuals who had no symptoms during the study period was 17.0% (95% CI = 11.2 – 23.4). The proportion of donors with anti-SARS-CoV-2 antibodies in two nearby blood banks of the Oise department was 3.0% (95% CI = 1.1 - 6.4). Interpretation: The relatively low IAR observed in an area where SARS-CoV-2 actively circulated weeks before confinement measures indicates that establishing herd immunity will take time, and that lifting these measures in France will be long and complex. Trial Registration: This study was registered with ClinicalTrials.gov (NCT04325646). Funding Statement: OS lab is funded by Institut Pasteur, ANRS, Sidaction, the Vaccine Research Institute (ANR10-LABX-77), Labex IBEID (ANR-10-LABX-62-IBEID), “TIMTAMDEN” ANR-14-CE14-0029, “CHIKV-ViroImmuno” ANR-14-CE14-0015-01 and the Gilead HIV cure program. LG is supported by the French Ministry of Higher Education, Research and Innovation.ME lab is funded by Institut Pasteur, Labex IBEID (ANR-10-LABX-62-IBEID), Reacting, EU grant Recover, ANR Oh’ticks. HM received core grants from the G5 Institut Pasteur Program, the Milieu Interieur Program (ANR-10-LABX-69-01) and INSERM. C.P. is supported by a fellowship from the Agence Nationale de Recherches sur le Sida et les Hepatites Virales (ANRS). SVDW lab is funded by Institut Pasteur, CNRS, Universite de Paris, Sante publique France, Labex IBEID (ANR-10-LABX-62-IBEID), REACTing, EU grant Recover. Declaration of Interests: The authors declare no competing interests. Ethics Approval Statement: Ethical approval by the Comite de Protection des Personnes Ile de France III. Informed consent was obtained from all participants.