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Feature Global Health

Covid-19: how doctors and healthcare systems are tackling coronavirus worldwide

BMJ 2020; 368 doi: (Published 18 March 2020) Cite this as: BMJ 2020;368:m1090

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Covid-19 Worldwide: we need precise data by age group and sex urgently

Dear Editor
Accurate and interpretable data are essential in guiding our approach to the COVID-19 pandemic (COVID-19 worldwide). Currently, basic epidemiological principles(1) are being flouted. Mostly, as in your article, case numbers are being reported. This number needs to be converted to a proportion by using the population size as the denominator. Otherwise, how can we tell which countries are being affected the most?
When the rate of disease is highly variable by age, as in Covid-19, we need to examine age specific mortality/morbidity and case fatality rates. Given the difference between males and females these rates also need to be stratified by sex. Age adjustment, either by the direct or indirect method or statistical models, is too crude when the rates are highly variable across age groups,(1) although it is a step forward compared with overall/crude rates that we are currently seeing, invariably in the media but also in professional journals.
We are being misled about the potential dangers (or not) by using overall/crude mortality rates. For example, the Chinese overall mortality proportions will not apply to countries with older age structures e.g. Italy or the UK, where mortality will be higher. The Italian proportions will not apply to much of Africa, where the average age of the population is low. Data should be published in the 10-year age groups or even better five-year age groups. The data are likely to be reassuring for parents and young people, and the opposite for older people. The results are likely to be much more informative than the widely disseminated and extremely crude estimate of 1-2% mortality or even lower, which is mostly based on China’s experience. We can and must do better.

1. Bhopal RS. Concepts of epidemiology : integrating the ideas, theories, principles and methods of epidemiology. 3rd edition ed. New York, NY: Oxford University Press; 2016.

Competing interests: No competing interests

22 March 2020
raj bhopal
Emeritus Professor of Public Health
Usher Institute, The University of Edinburgh
Edinburgh, EH39AG