Re:50% – 75% of cases of Covid-19 are asymptomatic
by nostromo on Tuesday March 17, 2020 @02:34AM
(#22602339)
That report was from summer 2009, so it was written during the outbreak. Note the early CFR from WHO was 0.4% for the US and over 1% for Mexico.
Later in the year it was found to be <0.03%.
Re:50% – 75% of cases of Covid-19 are asymptomatic
by wahern on Tuesday March 17, 2020 @02:58AM
(#22602441)
AFAICT, that 0.03% is for the U.K, not the U.S. And it doesn't say what the definition of CFR was. I've read a significant number of papers (primary materials) about SARS, MERS, H1N1, and influenza over the past few weeks. IME, CFR is usually defined as diagnosed or symptomatic cases as the denominator (which, as I've said, was until recently effectively equivalent), especially mid pandemic. But it's not always so defined. One notable exception that adds to the confusion is seasonal influenza, where U.S. annual fatality rates are calculated using post hoc modeling.
Even if we pin down CFR to be # deaths / # confirmed symptomatic, there's obviously still going to be some variability, possibly significant--quality of medical interventions, age distribution, etc. But trying to shoehorn IFR and other definitions into that number would compound such problems many fold.
Re:50% – 75% of cases of Covid-19 are asymptomatic
by paul_f on Wednesday March 18, 2020 @06:01AM
(#22615067)
Knowing the actual CFR allows us to set the right policy. The seasonal flu has a range of 0.10 and 0.015% CFR. At what point do we shut down society? 0.4% 0.6%?
And I know this will get me down=voted, but what if COVID-19 is everywhere already and it turns out the CFR to be close, or even lower than influenza?
Here's a paper from 2013 that surveyed CFR reports for H1N1: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3809029/ After a long discussion about the varying definitions of the numerator and denominator, they had this to say:
> Given that estimates of the infection fatality risk are unlikely to be available early enough for decision-making in a pandemic, a more feasible solution may be to measure the case fatality risk among symptomatic cases. ... Such estimates based on symptomatic cases may provide timely but imprecise estimates of seriousness for risk assessment.
CFR is not population mortality, and is usually not even infection fatality rate--but, confusingly, sometimes is as there's no official definition. After COVID-19 passes I suspect and hope that the medical community will tighten down definitions. CFR should be restricted to symptomatic cases approximating the type of severity that consumes non-negligible medical resources. Early on in an outbreak it's the only possible practical definition for tactical management of medical resources. An ER doctor couldn't care less how many infected people are convalescing at home. IFR (infection fatality rate) should be explicitly broken out. It's an important numbers to have, but often impossible to pin down until late in the game, sometimes only after the epidemic has passed. And IFR is most useful combined with r0, which has it's own definitional problems--do you care about hypothetical r0, r0 with social distancing, etc. Population mortality rate is even more difficult pin down.
I'm not a doctor, but I feel like "CFR" is one of those terms which was never meant to be consumed by the public. Early on it was probably taken for granted by the medical and scientific community to be a "case" as understood by doctors, who would typically only diagnose a specific illness when a patient presented with moderate or severe symptoms that required intervention. But as the medical and scientific community grew more diverse (and lab tests grew increasingly cheaper) the implied assumptions behind "case" became less and less valid, and they completely fall away in public discourse. These types of definitional problems are familiar to those of us in the tech sphere.