Updated: 22nd  March: Estimating COVID-19 Case Fatality  Rates (CFR) and Infection Rate Fatality (IFR)
 
The  Infection Rate Fatality (IFR) differs from the CFR in that aims to estimate the fatality rate in all those with infection: the detected disease (cases) and those with an undetected disease (asymptomatic and not tested group). if tested, this group would be counted as infected and at least temporarily be immune.
 
Our current best assumption, as of the 22nd March, is the IFR  is approximate 0.20% (95% CI, 0.17 to 0.25).*
 
In the elderly, co-morbidities have a significant impact on the CFR: those with ≥ 3 comorbidities are at much higher risk, particularly those with cardiovascular conditions. Modelling the data on the prevalence of comorbidities is essential to understand the CFR and IFR by age. In those without pre-existing health conditions, and over 70, the data is reassuring that the IFR will likely not be above 1%. The prevalence of comorbidities is highly age-dependent and is higher in socially deprived.
 
How do we arrive at this estimated IFR figure?  
 
The current COVID outbreak seems to be following previous pandemics in that initial CFRs start high and then trend downward. In Wuhan, for instance, the CFR  has gone down from 17% in the initial phase to near 1% in the late stage. Current testing strategies are not capturing everybody. At least 50% of those on the Diamond Princess was.  asymptomatic, who usually wouldn’t get a test.
 
In South Korea, considerable numbers who tested positive were also asymptomatics.  Asymptomatic people and mild cases are likely driving the rapid worldwide spread.
 
Early IFR rates are subject to selection bias as more severe cases are tested – generally those in the hospital settings or those with more severe symptoms. Mortality in children seems to be near zero (unlike flu) which will drive down the IFR significantly. In Swine flu, the IFR was fivefold less than the lowest estimate in the 1st ten weeks (0.1%)
 
Therefore, to estimate the IFR, we used the estimate from Germany’s current data 22nd March (93 deaths 23129) cases); CFR 0.40% (95% CI, 0.33% to 0.49%) and halved this for the IFR of 0.20% (95% CI, 0.17% to 0.25%) based on the assumption that half the cases go undetected by testing and none of this group dies. Our assumptions, however, do not account for some exceptional cases, as in Italy, where the population is older, smoking rates are higher, comorbidities may be higher, and antibiotic resistance is the highest in Europe, which all can act to increase the CFR and the subsequent IFR.
 
Given the estimated mortality in over 80’s is higher (CFR near 15%); there is considerable uncertainty over the IFR  rates in this group. It is currently not clear what the excess mortality is in this group.
 
It is essential to understand whether the elderly are dying with or from the disease (see the Sarah Newy report). It is also not clear if the presence of other circulating influenza illnesses acts to increase the CFR (testing for co-pathogens is not occurring), and whether certain populations (e.g., those with heart conditions) are more at risk. Understanding this issue is now critical. If, for instance, 80% of those over 80 died with the disease (20% from it) then the CFR  in >80s would be near 3% as opposed to 15%. This would then lower the overall CFR substantially.
 
*Estimating CFR and IFR in the early stage of outbreaks is subject to considerable uncertainties, the estimates are likely to change as more data emerges. The current prediction interval based on the available has a wide-ranging estimate of the CFR from 0.60 to 7.19. the corresponding IFR estimate based on this data would be 0.30 to 3.60.
 
See Lancet report:  CFRs on mortality rate estimates can be misleading if the CFR is based on the number of deaths per number of confirmed cases at the same time.  Using the denominator of the mortality rate as the total number of patients infected at the same time as those who died would lead to much higher CFRs. However, they report the full denominator remains unknown as asymptomatic with mild symptoms might not be tested and will not be identified, particularly in the early stages of an outbreak.

Coronavirus : “l'épidémie s'accélère trop vite, on fait de la médecine de catastrophe”

La répartition des patients est d'autant plus problématique qu'il n'existe pas en France d'outil permettant de savoir où il y a des places de réanimation libres. Les réanimateurs passent un temps fou au téléphone pour les trouver.