Tracking the onset date of the community spread of SARS-CoV-2 in western countries

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) rapidly spread around the world during 2020, but the precise time in which the virus began to spread locally is difficult to trace for most countries. Here, we estimate the probable onset date of the community spread of SARS-CoV-2 for heavily affected countries from Western Europe and the Americas on the basis of the cumulative number of deaths reported during the early stage of the epidemic. Our results support that SARS-CoV-2 probably started to spread locally in all western countries analysed between mid-January and mid-February 2020, thus long before community transmission was officially recognised and control measures were implemented.

Fig. 1:. estimation of the exponential growth parameters of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) epidemics over time in selected countries. Red and blue symbols represent the log-transformed daily counts of new deaths and the estimated number of infections, respectively, for each country. The data were fitted on an exponential growth curve (red and blue lines, with the shaded area representing the 95% confidence intervals). The goodness of fit (r²), p-value, growth constant (GC), and estimated doubling time (EDT) for each country are presented for each graph. The gray dotted line indicates the date of the 1st reported SARS-CoV-2 case in each country.

Fig. 2:. timeline of the Coronavirus disease 2019 (COVID-19) pandemic in the analysed countries. The red dot represents the date of the 1st reported severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) case in each country. Our estimates of the onset date of community transmission considering one (TN1), 10 (TN10), and 100 (TN100) seeders are represented by the blue dots according to the legend. The blue bars indicate the 95% confidence intervals of date estimates.