Analysis of COVID-19 Transmission Sources in France by Self-Assessment Before and After the Partial Lockdown: Observational Study

Abstract

Background We developed a questionnaire on a web application for analyzing COVID-19 contamination circumstances in France during the second wave of the pandemic. Objective This study aims to analyze the impact on contamination characteristics before and after the second partial lockdown in France to adapt public health restrictions to further prevent pandemic surges. Methods Between December 15 and 24, 2020, after a national media campaign, users of the sourcecovid.fr web application were asked questions about their own or a close relative’s COVID-19 contamination after August 15, 2020, in France. The data of the contamination’s circumstances were assessed and compared before and after the second partial lockdown, which occurred on October 25, 2020, during the second wave of the pandemic and was ongoing on December 24, 2020. Results As of December 24, 2020, 441,000 connections on the web application were observed. A total of 2218 questionnaires were assessable for analysis. About 61.8% (n=1309) of the participants were sure of their contamination origin, and 38.2% (n=809) thought they knew it. The median age of users was 43.0 (IQR 32-56) years, and 50.7% (n=1073) were male. The median incubation time of the assessed cohort was 4.0 (IQR 3-5) days. Private areas (family’s or friend’s house) were the main source of contamination (1048/2090, 50.2%), followed by work colleagues (579/2090, 27.7%). The main time of day for the contamination was the evening (339/961, 35.3%) before the lockdown and was reduced to 18.2% (86/473) after the lockdown (P<.001). The person who transmitted the virus to the user before and after the lockdown was significantly different (P<.001): a friend (382/1317, 29% vs 109/773, 14.1%), a close relative (304/1317, 23.1% vs 253/773, 32.7%), or a work colleague (315/1317, 23.9% vs 264/773, 34.2%). The main location where the virus was transmitted to the users before and after the lockdown was significantly different too (P<.001): home (278/1305, 21.3% vs 194/760, 25.5%), work (293/1305, 22.5% vs 225/760, 29.6%), collective places (430/1305, 33% vs 114/760, 15%), and care centers (58/1305, 4.4% vs 74/760, 9.7%). Conclusions Modalities of transmissions significantly changed before and after the second lockdown in France. The main sources of contamination remained the private areas and with work colleagues. Work became the main location of contamination after the lockdown, whereas contaminations in collective places were strongly reduced. Trial Registration ClinicalTrials.gov NCT04670003; https://clinicaltrials.gov/ct2/show/NCT04670003

Incubation Period of COVID-19 Caused by Unique SARS-CoV-2 Strains

“…Based on the inclusion and exclusion criteria, 142 articles (8112 patients) were selected for analysis. 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , …”

“…Most of the studies (93 [65.5%]) were conducted between January and March 2020 and most were conducted in China (108 [76.1%]). One study used case data from multiple countries around the world, 81 6 studies were conducted in South Korea, 37 , 46 , 51 , 52 , 59 , 124 4 in France, 25 , 29 , 35 , 113 3 in Japan, 80 , 105 2 in Singapore, 87 , 111 2 in India, 16 , 78 , 83 , 103 2 in Vietnam, 21 , 58 and 2 in Australia. 45 , 99 One hundred nineteen studies (83.8%) included patients infected with the wild-type strain, 5 (3.5%) with the multiple strains, 17 , 26 , 35 , 80 , 112 and 11 (7.7%) with an unknown strain 84 , 93 , 99 , 106 , 116 , 126 , 135 , 142 , 148 , 150 , 157 (eTable 4 in the Supplement ).…”

“…We identified 5012 records through PubMed, EMBASE, and Science Direct database searches, and documented the study selection process in a flowchart and showed the total numbers of retrieved references and the numbers of included and excluded studies (Figure 1). Based on the inclusion and exclusion criteria, 142 articles (8112 patients) were selected for analysis …”

Lessons from a pandemic

“…Specific studies might be necessary, before generalizing certain parameters for distant countries (from north to south for example). Others could be obtained through specific surveys, such as the frequency of population participation in a mass event, the proportion of infections occurring within a household, or by investigating the sources of contamination [28]. Finally, some information should simply be guessed or assumed on the basis of the scientific literature, with the possibility (and duty) of being updated to become more and more accurate along the course of the pandemic.…”

Lessons from a pandemic

“…Some could be borrowed from other countries, such as the average duration of contagion of the disease. Others could be obtained through specific surveys, such as the frequency of population participation in a mass event, the proportion of infections occurring within a household, or by investigating the sources of contamination [28]. Finally, some information should simply be guessed or assumed on the basis of the scientific literature, with the possibility (and duty) of being updated to become more and more accurate along the course of the pandemic.…”