Thread by @covidperspectiv

* CASE FATALITY RATE (CFR) - A THREAD *

Case fatality has been the subject of much discussion. For example, a 3.4% fatality rate was given recently by the World Health Organization.

This was calculated by the total fatalities (eg 3,387), divided by the # of cases (98,118).

2. There are two main issues with this.

FACTOR ONE

Many cases are unknown, eg. mild cases that have not been detected, or a straightforward lack of testing capacity. This tends to make the actual CFR lower than originally calculated. (The denominator in this case is higher).

3.

FACTOR TWO

It takes time for the disease to reach critical, eg. 3-4 weeks from 1st symptoms. This skews the number of fatalities, as they would be higher in 3-4 weeks. This has the effect to make the actual CFR higher than calculated. (The numerator in this case is higher)

4. These two factors have the effect to partly cancel each other out. How much is not known, at this point.

5. Another factor that affects CFR generally is the level of healthcare available. CFR will be higher if individuals cannot receive good healthcare, or the healthcare system is overloaded.

6. With #COVID19, it has been widely reported that CFR varies substantially by age, with those over 80 at most risk. Pre-existing medical conditions also increase CFR. A history of smoking may increase CFR. Men have shown generally higher risk than women.

7. Here are some recent CFR rates for #COVID19 as reported by China’s CDC.

0-9 ......... 0%
10-19 ...... 0.2%
20-29 ..... 0.2%
30-39 ..... 0.2%
40-49 ..... 0.4%
50-59 ..... 1.3%
60-69 ..... 3.6%
70-79 ...... 8.0%
80+ ......... 14.8%

Men overall: 2.8%
Women overall: 1.7%

8. We hope this quick primer was helpful. For more on the subject, the following articles have more detail.

Coronavirus Death Rate Explained
vox.com/2020/3/5/21165…

Coronavirus by the Numbers
nytimes.com/2020/03/05/hea…

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