dcyphr | Estimating the ascertainment rate of SARS-CoV-2 infection in Wuhan, China: implications for management of the global outbreak


The coronavirus disease 2019 (COVID-19) outbreak originated in the city of Wuhan at the end of 2019, China, and is now a global pandemic. The scientists explain that the Infection Fatality Rate (IFR) is the number of deaths as a proportion of all persons infected with the SARS-CoV-2 novel coronavirus. Case Fatality Rate (CFR) is the proportion among confirmed cases. According to the scientists, the IFR can be lower than the CFR if many SARS-CoV-2 infections with mild or no symptoms are not being detected. The scientists' aim was to estimate the ascertainment rate by applying epidemic modeling to publicly reported confirmed COVID-19 cases in Wuhan. Their secondary aim was to estimate among other epidemic parameters, the basic reproduction number R0. 


The scientists used the most recent confirmed case data from Wuhan using the R package ‘nCov2019’, for the period between 3 January and 9 March 2020. Wuhan was chosen because after the lockdown that started on 23 January 2020 the cases showed a steady decline since mid-February. 


The scientists estimated that for Wuhan the ascertainment rate is at 0.465%. According to the scientists this shows that for every confirmed case in Wuhan there had been 200 infections that were not detected. Scientists found that the R0 was estimated at 3.07. The scientists estimated that the R0 would be 5.33 until the Wuhan lockdown, decreasing to 2.09 until 10 February rising to 3.83 later, with an ascertainment rate of 0.48%. According to the their results, half of Wuhan's population was already infected by 27 January, while at 23 February only 585,000 of these remained. This would mean that 94.7% of the population had been infected but if the contact between people dropped to 85% after the lockdown, the percentage would be 52.7%.


The scientists proposed that a possible scenario for Wuhan's outbreak control was the fact that a large majority of the population was infected, and only a small percentage of infections were detected, without this meaning that the measures taken did not help to "flatten the curve".

According to the scientists, it is crucial to estimate the case ascertainment to accurately assess the true nature of the COVID-19 pandemic. Based on their findings scientists claim that testing and contact tracing are probably not the best solution, and it could lead to take us further away from the initial goal which to “flatten the curve” as much as possible, so that the health care systems are not burdened and the most vulnerable people are protected.

The scientist conclude that more surveys like this should take pace in order to find out the true size of infection in different population, as the ascertainment rate they estimated for Wuhan is on the lower end of what was previously published.