WHY 🦠 CFR MATH IS HARD: Uncertainties of naive case count estimates. Graph shows how the ratio of the number of confirmed deaths and case counts changed over time. Case counts are corrected for 3-fold or 30-fold under-reporting and diagnostic delay 🧵: smw.ch/article/doi/sm… 
2) ...In addition, example of diagnosis taken 2, 4, and 7 days prior to the date of the count of confirmed death. The latter is meant to illustrate the effect of the delay between diagnosis and death or recovery. *This actual delay is likely longer than one week*.
3) Implication is that while a) underdiagnosis will mean the real CFR is lower, b) a longer delay from diagnosis to death/recovery will mean the real CFR is higher. Hence there is a tug of war between A vs B above for estimating true CFR. That’s why we can’t know true CFR yet.
4) Authors argue: “The higher case fatality rate reported from Wuhan may be overestimated. The true number of exposed cases may be vastly underestimated. With a focus on serious cases, mild/asymptomatic courses might remain largely unrecognized, in particular during flu season.”
4) Authors continue: “Under-detection of mild or asymptomatic cases may be further fueled after further growth of the outbreak, as healthcare-facilities and testing capacities in Wuhan have reached their limits.”
5) On flip side, authors argue: “The lower case fatality rates outside Wuhan may be *underestimated*... As the epidemic arrived later in other regions and countries, there may be a delay of fatal cases arising and their reporting...
6) Moreover, the authors argue that “The low number of documented recovered cases might indicate that days and weeks can pass until death occurs. Hence, the numbers, e.g. Guangdong with 970 cases and no death occurring, might be false low because severe cases might still [die].”
7) Finally, “Case fatality rates may truly differ among different regions of the world. Differences in CFR may be caused by differences in medical care during a large epidemic versus care for single cases.” Special thx to first author @MBattegay for publishing this great piece!
8) For extended discussion, @DellAnnaLuca has a detailed thread 🧵 on this CFR issue. The LAG again is much longer than just 1 week to resolution of the virus 🦠 unfortunately. Bottom line, don’t go by the naive 2% mortality so far.
