The many estimates of the COVID-19 case fatality rate
Authors: Dimple D Rajgor, Meng Har Lee, Sophia Archuleta, Natasha Bagdasarian, Swee Chye Quek
Journal: The Lancet Infectious Diseases (2020)

Since the outbreak of coronavirus disease 2019 (COVID-19) began in December, a question at the forefront of many people's minds has been its mortality rate. Is the mortality rate of COVID-19 higher than that of influenza, but lower than that of severe acute respiratory syndrome (SARS)? The trend in mortality reporting for COVID-19 has been typical for emerging infectious diseases. The case fatality rate (CFR) was reported to be 15% (six of 41 patients) in the initial period,1Huang C Wang Y Li X et al.Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China.Lancet. 2020; 395: 497-506Summary Full Text Full Text PDF PubMed Scopus (32861) Google Scholar but this estimate was calculated from a small cohort of hospitalised patients. Subsequently, with more data emerging, the CFR decreased to between 4·3% and 11·0%,2Chen N Zhou M Dong X et al.Epidemiological and clinical characteristics of 99 cases of 2019 novel coronavirus pneumonia in Wuhan, China: a descriptive study.Lancet. 2020; 395: 507-513Summary Full Text Full Text PDF PubMed Scopus (14363) Google Scholar, 3Wang D Hu B Hu C et al.Clinical characteristics of 138 hospitalized patients with 2019 novel coronavirus-infected pneumonia in Wuhan, China.JAMA. 2020; (published online Feb 7.)DOI:10.1001/jama.2020.1585Crossref Scopus (16201) Google Scholar and later to 3·4%.4WHOWHO Director-General's opening remarks at the media briefing on COVID-19.https://www.who.int/dg/speeches/detail/who-director-general-s-opening-remarks-at-the-media-briefing-on-covid-19---3-march-2020Date: March 3, 2020Date accessed: March 11, 2020Google Scholar The rate reported outside China in February was even lower (0·4%; two of 464).5Johns Hopkins Center for Systems Science and EngineeringCoronavirus COVID-19 global cases.https://gisanddata.maps.arcgis.com/apps/opsdashboard/index.html#/bda7594740fd40299423467b48e9ecf6Date: 2020Date accessed: March 11, 2020Google Scholar This pattern of decreasing CFRs is not surprising during the initial phase of an outbreak. Hard outcomes such as the CFR have a crucial part in forming strategies at national and international levels from a public health perspective. It is imperative that health-care leaders and policy makers are guided by estimates of mortality and case fatality. However, several factors can restrict obtaining an accurate estimate of the CFR. The virus and its clinical course are new, and we still have little information about them. Health care capacity and capability factors, including the availability of health-care workers, resources, facilities, and preparedness, also affect outcomes. For example, some countries are able to invest resources into contact tracing and containing the spread through quarantine and isolation of infected or suspected cases. In Singapore, where these measures have been implemented, the CFR of 631 cases (as of March 25, 2020) is 0·3%. In other places, testing might not be widely available, and proactive contact tracing and containment might not be employed, resulting in a smaller denominator and skewing to a higher CFR. The CFR can increase in some places if there is a surge of infected patients, which adds to the strain on the health-care system and can overwhelm its medical resources. A major challenge with accurate calculation of the CFR is the denominator: the number of people who are infected with the virus. Asymptomatic cases of COVID-19, patients with mild symptoms, or individuals who are misdiagnosed could be left out of the denominator, leading to its underestimation and overestimation of the CFR. A unique situation has arisen for quite an accurate estimate of the CFR of COVID-19. Among individuals onboard the Diamond Princess cruise ship, data on the denominator are fairly robust. The outbreak of COVID-19 led passengers to be quarantined between Jan 20, and Feb 29, 2020. This scenario provided a population living in a defined territory without most other confounders, such as imported cases, defaulters of screening, or lack of testing capability. 3711 passengers and crew were onboard, of whom 705 became sick and tested positive for COVID-19 and seven died,6CNADiamond Princess passenger dies, bringing ship's death toll to seven.https://www.channelnewsasia.com/news/asia/coronavirus-covid19-japan-diamond-princess-deaths-12513028Date: March 8, 2020Date accessed: March 11, 2020Google Scholar giving a CFR of 0·99%. If the passengers onboard were generally of an older age, the CFR in a healthy, younger population could be lower.7Pappas S How deadly is the new coronavirus?.https://www.livescience.com/is-coronavirus-deadly.htmlDate: March, 2020Date accessed: March 11, 2020Google Scholar Although highly transmissible, the CFR of COVID-19 appears to be lower than that of SARS (9·5%) and Middle East respiratory syndrome (34·4%),8Munster VJ Koopmans M van Doremalen N van Riel D de Wit E A novel coronavirus emerging in China—key questions for impact assessment.N Engl J Med. 2020; 382: 692-694Crossref PubMed Scopus (942) Google Scholar but higher than that of influenza (0·1%).9de Wit E van Doremalen N Falzarano D Munster VJ SARS and MERS: recent insights into emerging coronaviruses.Nat Rev Microbiol. 2016; 14: 523-534Crossref PubMed Scopus (2394) Google Scholar, 10Fauci AS Lane HC Redfield RR Covid-19—navigating the uncharted.N Engl J Med. 2020; (published online Feb 28.)DOI:10.1056/NEJMe2002387Crossref PubMed Scopus (1218) Google Scholar We declare no competing interests. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, ChinaThe 2019-nCoV infection caused clusters of severe respiratory illness similar to severe acute respiratory syndrome coronavirus and was associated with ICU admission and high mortality. Major gaps in our knowledge of the origin, epidemiology, duration of human transmission, and clinical spectrum of disease need fulfilment by future studies. Full-Text PDF Ratio, rate, or risk?In epidemiology, the terms ratio, rate, and risk have clear definitions.1 In the emerging publications related to coronavirus disease 2019 (COVID-19), the phrase case fatality rate is being used instead of case fatality ratio.2,3 A ratio is a comparison of two similar quantities. Ratios have no dimensions and can take any value; a ratio of 1 means the two quantities being compared are equal to each other. The case fatality ratio is the ratio of deaths (numerator) to identified cases (denominator), and is usually expressed as percentage. Full-Text PDF