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Cluster of COVID-19 in northern France: A retrospective closed cohort study

Arnaud Fontanet 1, 2, * Laura Tondeur 1 Yoann Madec 1 Rebecca Grant 1, 3 Camille Besombes 1 Nathalie Jolly 4 Sandrine Fernandes Pellerin 4 Marie-Noëlle Ungeheuer 5 Isabelle Cailleau 6 Lucie Kuhmel 7 Sarah Temmam 8 Christèle Huon 8 Kuang-Yu Chen 9 Bernadette Crescenzo 10 Sandie Munier 10 Caroline Demeret 10 Ludivine Grzelak 11, 12 Isabelle Staropoli 11, 12 Timothée Bruel 11, 12 Pierre Gallian 13, 14 Simon Cauchemez 15 Sylvie van der Werf 10 Olivier Schwartz 11, 12 Marc Eloit 8, 16 Bruno Hoen 1
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 midJanuary 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.
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Contributor : Caroline Demeret <>
Submitted on : Friday, February 19, 2021 - 3:32:45 PM
Last modification on : Thursday, April 15, 2021 - 3:08:17 PM

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Arnaud Fontanet, Laura Tondeur, Yoann Madec, Rebecca Grant, Camille Besombes, et al.. Cluster of COVID-19 in northern France: A retrospective closed cohort study. 2021. ⟨pasteur-03147081⟩

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