Early chains of transmission of COVID-19 in France, January to March 2020

Abstract

Introduction SARS-CoV-2, the virus that causes COVID-19, has spread rapidly worldwide. In January 2020, a surveillance system was implemented in France for early detection of cases and their contacts to help limit secondary transmissions. Aim To use contact-tracing data collected during the initial phase of the COVID-19 pandemic to better characterise SARS-CoV-2 transmission. Methods We analysed data collected during contact tracing and retrospective epidemiological investigations in France from 24 January to 30 March 2020. We assessed the secondary clinical attack rate and characterised the risk of a contact becoming a case. We described chains of transmission and estimated key parameters of spread. Results During the study period, 6,082 contacts of 735 confirmed cases were traced. The overall secondary clinical attack rate was 4.1% (95% confidence interval (CI): 3.6–4.6), increasing with age of index case and contact. Compared with co-workers/friends, family contacts were at higher risk of becoming cases (adjusted odds ratio (AOR): 2.1, 95% CI: 1.4–3.0) and nosocomial contacts were at lower risk (AOR: 0.3, 95% CI: 0.1–0.7). Of 328 infector/infectee pairs, 49% were family members. The distribution of secondary cases was highly over-dispersed: 80% of secondary cases were caused by 10% of cases. The mean serial interval was 5.1 days (interquartile range (IQR): 2–8 days) in contact tracing pairs, where late transmission events may be censored, and 6.8 (3–8) days in pairs investigated retrospectively. Conclusion This study increases knowledge of SARS-CoV-2 transmission, including the importance of superspreading events during the onset of the pandemic.

Seroprevalence Survey of Anti-SARS-CoV-2 Antibodies in a Population of Emilia-Romagna Region, Northern Italy

“…Our results also showed a different distribution by age group, with higher seroprevalence in older individuals, particularly those aged 60-69 years and >70 years (18.6% and 18.0%, respectively). In France, during the first wave, the risk of becoming a case was higher for contacts aged 60-74 years (adjusted odds ratio-AOR: 2.0, 95% CI: 1.2-3.3), and older than 75 years (AOR: 2.1, 95% CI: 1.1-3.9), compared with the reference group of 15-29 years [32]. Further relevant data concerned the high seroprevalence of individuals aged <20 years (17.1%).…”

SARS-CoV-2 and the role of close contact in transmission: a systematic review

“…The positive findings from studies that performed GS and phylogenetic analysis with identical strains supports the hypothesis that SARS-CoV-2 transmission occurs in close contact settings. The routes of transmission are unclear but may include direct and indirect contact and/or large droplet or short-range aerosol transmission as possible explanations for the identified identical strains in close contacts [3][4][5] . The failure of the majority of studies to report Ct values casts doubts on the strengths of any reported associations because of the likelihood of false positives, as is the lack of (and variation in) reporting of the timelines for sample collections.…”

“…Helsingen 2020 3 Paireau 2020 4 Kuwelker 2020 5 Lyngse 2020 6 Jones 2020 7 Chen 2020 8 Fontanet 2020 9 Armann 2020 10 Charlotte 2020 11 Angulo-Bazan 2020 12…”

“…Many national governments have implemented prevention and control measures and vaccines are now being approved and administered; the overall global spread of the virus now appears to be slowing 2 , but the virus continues to evolve. Current evidence from epidemiologic and virologic studies suggest SARS-CoV-2 is primarily transmitted via exposure to infectious respiratory fluids such as fine aerosols and respiratory droplets, and to a lesser extent through fomites; however, the relative contributions of the different modes of transmission is not completely understood [3][4][5] . Controversy still exists about how the virus is transmitted and the relative frequency of the modes of transmission and if these modes may be altered in specific settings 6,7 .…”

“…Necessary updates Several of the preprints included in the systematic review and/or cited in the manuscript have been published; given that this manuscript is outdated and an update is needed, authors should take that opportunity to update preprints that have been published and make sure their findings remain unchanged and adjust accordingly. Some of the preprints now published are: Helsingen 2020 3 Paireau 2020 4 Kuwelker 2020 5 Lyngse 2020 6 Jones 2020 7 Chen 2020 8 Fontanet 2020 9 Armann 2020 10 Charlotte 2020 11 Angulo-Bazan 2020 12 …”