Skip directly to site content Skip directly to page options Skip directly to A-Z link Skip directly to A-Z link Skip directly to A-Z link
Volume 26, Number 6—June 2020
Research Letter

Case-Fatality Risk Estimates for COVID-19 Calculated by Using a Lag Time for Fatality

Author affiliations: University of Otago Department of Public Health, Wellington, New Zealand

Cite This Article

Abstract

We estimated the case-fatality risk for coronavirus disease cases in China (3.5%); China, excluding Hubei Province (0.8%); 82 countries, territories, and areas (4.2%); and on a cruise ship (0.6%). Lower estimates might be closest to the true value, but a broad range of 0.25%–3.0% probably should be considered.

The coronavirus disease (COVID-19) is spreading globally; as of March 5, 2020, cases were reported in China and 85 other countries, territories, and areas (1). Disease severity is a particularly crucial parameter for understanding this new disease (2), but accurately estimating the case-fatality risk is difficult because milder cases are not being diagnosed and death is delayed.

We used data from the World Health Organization (WHO) (1) to calculate crude estimates of the case-fatality risk on March 5, 2020, for 4 populations: China; China, excluding Hubei Province; a group of 82 countries, territories, and areas; and passengers and crew of a cruise ship (Table). However, given the critical need to consider time lags to death when calculating case-fatality risk (3), we used time lags from a recent study from China (4). Yang et al. (4) reported that the median time from symptom onset to radiological confirmation of pneumonia was 5 days (interquartile range [IQR] 3–7 days); from symptom onset to intensive care unit (ICU) admission was 11 days (IQR 7–14 days); and from ICU admission to death was 7 days (IQR 3–11 days). Therefore, a median of 13 days passed from pneumonia confirmation to death ([11–5] + 7 = 13).

For our calculation, we assumed that the day of radiological confirmation of pneumonia approximately equated to the reporting date for laboratory-confirmed cases of COVID-19 to WHO. We obtained cumulative COVID-19 case counts reported by WHO on February 21 (5), which was 13 days before March 5, the date we used for calculating the crude case-fatality risk. Our approach is broadly comparable to a study that used earlier data to estimate the median time delay of 13 days from illness onset to death (6).

By using the number of cumulative cases on February 21 as the denominator for the adjusted case-fatality risk (aCFR), we assumed that half of the additional cumulative reported deaths on March 5 could be matched with cases reported on February 21. We acknowledge our approach is fairly simplistic and that it can be superseded when higher quality cohort-based analyses become available.

The case-fatality risks, when adjusted for a 13-day lag time from reporting to death, were 3.5% in China; 0.8% in China, excluding Hubei Province; 4.2% in the group of 82 countries, territories, and areas; and 0.6% for the cruise ship (Table). Our result for China, excluding Hubei Province, is similar to a previous estimate of 0.9% (95% CI 0.6%–1.3%) by using a time-delay adjusted case-fatality risk for the same area (K. Mizumoto and G. Chowell, unpub. data; https://www.medrxiv.org/content/10.1101/2020.02.19.20025163v1).

Of our results, the least generalizable might be the result for China, which could be elevated because of undiagnosed mild cases, initial shortages of test kits, and elevated risk for death due to initial high demands on the healthcare system in Wuhan. The aCFR for the group of 82 countries, territories, and areas also might be affected by missed mild cases if some of the areas had undetected transmission. In terms of undiagnosed mild cases, the aCFR for the cruise ship population likely is the most accurate even though the 95% CI is broad. In addition, the aCFR for the cruise ship had a higher denominator due to inclusion of asymptomatic test-positive cases. Among 3,711 crew and passengers, 255 asymptomatic cases were identified (7); some of these persons subsequently might have developed symptoms. Thus, the aCFR for the cruise ship partially could reflect an infection-fatality risk. Also of note, 2,165 persons on the cruise ship were >60 years of age (7), and data from China indicates a much higher case-fatality risk among this age group (8); thus, a higher case-fatality risk might be expected in the cruise ship population than in other communities sampled. Considering these issues of generalizability, the aCFR of 0.8% for China, excluding Hubei Province, might be most accurate.

Nevertheless, given the residual uncertainties, health sector decision-makers and disease modelers probably should consider a broad range of 0.25%–3.0% for COVID-19 case-fatality risk estimates. The higher values could be more appropriate in resource poor settings where the quality of hospital and intensive care might be constrained. Higher values might also be appropriate in high-income countries with limited surge capacity in hospital services because elevated case-fatality risks could be seen at the peak of local epidemics. Because COVID-19 is expected to further spread globally, ongoing work using country-specific cohorts will be needed to more robustly clarify the case-fatality risk of this new disease.

Dr. Wilson is a professor of public health at the University of Otago, New Zealand. He has a long-standing research interest in historical and contemporary pandemics.

Top

Acknowledgment

This report was done as part of work for the New Zealand Ministry of Health (contract and funding support pending at the time of submission).

Top

References

  1. World Health Organization. Coronavirus disease 2019 (COVID-19) situation report—45, 5 Mar 2020 [cited 2020 Mar 6]. https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200305-sitrep-45-covid-19.pdf
  2. Cowling  BJ, Leung  GM. Epidemiological research priorities for public health control of the ongoing global novel coronavirus (2019-nCoV) outbreak. Euro Surveill. 2020;25: Epub ahead of print. DOIPubMedGoogle Scholar
  3. Donnelly  CA, Ghani  AC, Leung  GM, Hedley  AJ, Fraser  C, Riley  S, et al. Epidemiological determinants of spread of causal agent of severe acute respiratory syndrome in Hong Kong. Lancet. 2003;361:17616. DOIPubMedGoogle Scholar
  4. Yang  X, Yu  Y, Xu  J, Shu  H, Xia  J, Liu  H, et al. Clinical course and outcomes of critically ill patients with SARS-CoV-2 pneumonia in Wuhan, China: a single-centered, retrospective, observational study. Lancet Respir Med. 2020;S2213-2600(20)30079-5; Epub ahead of print. DOIPubMedGoogle Scholar
  5. World Health Organization. Coronavirus disease 2019 (COVID-19) situation report—32, 21 Feb 2020 [cited 2020 Mar 6]. https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200221-sitrep-32-covid-19.pdf
  6. Linton  NM, Kobayashi  T, Yang  Y, Hayashi  K, Akhmetzhanov  AR, Jung  SM, et al. Incubation period and other epidemiological characteristics of 2019 novel coronavirus infections with right truncation: a statistical analysis of publicly available case data. J Clin Med. 2020;9:538. DOIPubMedGoogle Scholar
  7. National Institute of Infectious Diseases. Japan. Field briefing: Diamond Princess COVID-19 cases, 19 February 2020 [cited 2020 Feb 29]. https://www.niid.go.jp/niid/en/2019-ncov-e/9407-covid-dp-fe-01.html
  8. The Novel Coronavirus Pneumonia Emergency Response Epidemiology Team. The epidemiological characteristics of an outbreak of 2019 novel coronavirus diseases (COVID-19)—China, 2020. China CDC Weekly 2020 [cited 2020 Feb 29]. http://weekly.chinacdc.cn/en/article/id/e53946e2-c6c4-41e9-9a9b-fea8db1a8f51

Top

Table

Top

Cite This Article

DOI: 10.3201/eid2606.200320

Original Publication Date: March 13, 2020

Table of Contents – Volume 26, Number 6—June 2020

EID Search Options
presentation_01 Advanced Article Search – Search articles by author and/or keyword.
presentation_01 Articles by Country Search – Search articles by the topic country.
presentation_01 Article Type Search – Search articles by article type and issue.

Top

Comments

Please use the form below to submit correspondence to the authors or contact them at the following address:

Nick Wilson, Department of Public Health, University of Otago Wellington, Mein St, Newtown, Wellington 6005, New Zealand

Send To

10000 character(s) remaining.

Top

Page created: May 19, 2020
Page updated: May 19, 2020
Page reviewed: May 19, 2020
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.
file_external