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Case fatality risk (CFR) describes the risk of fatality among individuals diagnosed with COVID-19. These metrics can indicate crude trends in the risk of death with COVID-19 and are often used as international comparators.1 However, demographic factors and changing testing practices can lead to substantial discrepancies. Here, we highlight complexity of CFR interpretation, using England as an example.
We calculated CFRs for laboratory confirmed COVID-19 cases since the start of the second pandemic wave (week 27 onwards) in England.2 CFR was calculated using a 60-day lag time, following an individuals’ first positive specimen. CFR was stratified by age group and gender, and for those aged ≥80 years old, by long-term care facilities residency.
Overall, the CFR among all individuals with laboratory confirmed COVID-19 in the second wave of the epidemic in England was 1.4%. The highest CFR was among those aged ≥80 years old (17.2%; women: 13.2%, men: 24.8%) followed by those aged 70–79 years old (9.7%; women: 6.7%, men: 12.8%), and those aged 60–69 years old (2.4%; women: 1.8%, men: 3.0%). The lowest CFR was in those aged <50 years old (0.05%). CFRs were higher among men compared with women within all age groups.
Among those aged ≥80 years old, a lower CFR was observed among care home residents (11.6%) compared with non-residents (22.9%) (figure 1). This disparity is driven by a policy of monthly testing of care home residents, detecting more mild and moderate cases. For example, the CFR among individuals aged ≥80 years old diagnosed in outbreak investigations or as hospital admissions was similar for both care home residents and non-residents (33.1% and 31.0%, respectively). However, care home residents diagnosed through routine screening had a much lower CFR (8.8%), much closer to age-matched non-care home residents (3.8%).
The differences in observed CFR are multifactorial and reflective of differences in testing strategy and population demographics. Cases identified by wider population testing, regardless of age and care home residency status, will include people with a broader range of clinical severity (including those with mild or no symptoms) than those identified through outbreak investigation or inpatient hospital testing. Among the older population, this will be accentuated by active regular testing of care home residents.3
In conclusion, CFR is an informative indicator of crude mortality risk. However, it should be presented separately by age and sex, and interpreted carefully within the specific context of testing practices and healthcare provision. Thus, caution must be taken when comparing CFR between countries.
Contributors All authors reviewed the data and contributed to the data interpretation and writing. KH, HA and MK were all involved in data analysis and accessed the underlying data.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; internally peer reviewed.