2019-novel Coronavirus (2019-nCoV): Estimating the Case Fatality Rate – A Word of Caution (2020/02/07)

Estimating and predicting the extent and lethality of the 2019-Novel Coronavirus (2019-nCoV) outbreak, originating in Wuhan/China is obviously challenging, reflected by many controversial statements and reports. Unsurpassed to date, an ever-increasing flow of information, immediately available and accessible online, has allowed the description of this emerging epidemic in real-time [1]. The first patients were reported in Wuhan on December 31st 2019 [2]. Only a few days later, Chinese researchers identified the etiologic agent now known as the 2019-nCoV and published the viral sequence [3]. New data on the virus, its characteristics and epidemiology become available 24/7 and are often shared via informal platforms and media [4]. Yet, key questions remain largely unanswered.

How is the virus transmitted, how long is the incubation period, what is the role of asymptomatic infected, what is the definite reproductive number R0, how long is viral shedding persisting after fading of symptoms, who is at risk for a severe course, and ultimately, how high is the case fatality rate?

Accurate answers are critical for predicting the outbreak dynamics, to tailor appropriate and effective prevention measures, and to prepare for a potential pandemic. Precise estimates of the case fatality rate and the fraction of infections that require hospitalization are critical to balance the socioeconomic burden of infection control interventions against their potential benefit for mankind. Hence, one of the most important figures to determine is the rate of asymptomatic and mild cases allowing to put severe courses and death rates into accurate context.

At present, it is tempting to estimate the case fatality rate by dividing the number of known deaths by the number of confirmed cases. The resulting number, however, does not represent the true case fatality rate and might be off by orders of magnitude. Diagnosis of viral infection will precede recovery or death by days to weeks and the number of deaths should therefore be compared to the past case counts – accounting for this delay increasing the estimate of the case fatality rate. On the other hand, cases in official statistics are likely a severe underestimate of the total – accounting for this underestimate will decrease the case fatality rate. The time between diagnosis and death/recovery and the degree of underreporting will vary over time as well as between cities and countries. A precise estimate of the case fatality rate is therefore impossible at present. Figure 1 illustrates how these uncertainties manifest themselves using currently available data.

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Author: Manuel Battegay , Richard Kuehl ,  Sarah Tschudin-Sutter, et al.

Link: https://smw.ch/article/doi/smw.2020.20203