On Monday (March 28), Kong Fanyi, a clinical professor at the Department of Internal Medicine, Faculty of Medicine, University of Hong Kong, said that the actual number of people infected with the new coronavirus may have reached 4 million. He said that the overall mortality rate estimated by using this as the denominator is actually only 0.18%. , slightly higher than the fatality rate of seasonal flu.
The Chief Executive, Carrie Lam, later agreed with Kong Fanyi's view, acknowledging that the actual number of cases was higher than the number of reported cases and the mortality calculation should take this into account, but stressed that the official estimate that a quarter of the population was infected was lower than scholars' estimates.
According to the World Health Organization's August 2020 scientific briefing document Estimated Mortality Rates from Coronavirus Disease 2019 (COVID-19), there are two main methods that can be used to assess the proportion of people infected with the disease who die: The first is the Infection Fatality Ratio (IFR), which is the number of deaths due to the disease divided by the number of infections; the second is the Case Fatality Ratio (CFR), which is the number of deaths divided by Monitor the number of reported confirmed cases.
Kong Fanyi is a clinical professor at the Department of Internal Medicine, Faculty of Medicine, University of Hong Kong.
(File photo / Photo by Ojiale)
Infection ratio is more accurate but hard to know
The mortality calculation method supported by Kong Fanyi and Carrie Lam is actually the IFR mentioned in the WHO document, and the IFR is really more accurate for assessing the mortality rate of the epidemic.
The WHO more directly encouraged countries to "estimate the IFR where possible" last year, and cited the results of studies conducted in Geneva, Switzerland and Stockholm at that time, arguing that the estimated value of the new coronavirus IFR worldwide is about 0.5% to 1% about.
However, the WHO document also pointed out that "in order to accurately measure IFR, complete information on the number of infections and deaths from the disease must be known", and even population sampling serological testing should be performed to obtain more reliable figures. difficult to obtain during the epidemic.
While WHO agrees that the IFR can be "estimated using routine surveillance data to estimate disease severity," it also emphasizes that all parties must be clear "to account for possible bias in its estimation process."
At present, the Hong Kong government and experts are trying to adopt the calculation method of IFR, apparently without serological testing and other means to estimate the total number of infected people.
In addition, the estimated total number of infected people by the authorities and the university is more than doubled. In addition, the preliminary analysis of more than 30% of the death cases may not be directly related. It also shows that the accuracy of the denominator and numerator of the Hong Kong IFR is doubtful. If you are not ready to estimate an accurate IFR, you should not be too hasty to announce an IFR that is too low to the public, or even send the wrong message that the virus is of limited lethality.
Case ratio still has a reference role
Relative to the IFR, the CFR limits its denominator to the number of cases detected by surveillance systems, making it slightly less accurate at reflecting the overall severity of an infectious disease.
But it also makes CFR more able to highlight how lethal a sudden outbreak of an epidemic is to local patients, as well as to assess the specific effectiveness of the public health measures the authorities have implemented, as well as the ability to detect the epidemic. It can be said that it is different from the IFR for society. reference.
WHO believes that the overestimation of CFR is mainly due to non-reporting of mild or asymptomatic infections, and this problem has been overcome in Hong Kong in recent months by adopting rapid antigen testing; as for the underestimation of CFR, it is mainly due to infection The deceased died before the diagnosis was reported. However, the current method of finding out the death cases of the new crown in Hong Kong already includes the examination of the dead body.
Due to the above measures, the current CFR in Hong Kong is relatively accurate.
In fact, in order to prevent excessive fluctuations in the mortality calculation, the WHO also recommends that only the eliminated cases be counted during the epidemic, that is, the number of deaths divided by the number of deaths plus the number of recoveries to arrive at a temporary CFR, so as to avoid delays in various cases application-induced bias.
Of course, if this formula is placed in Hong Kong today, it will inevitably lead to a higher mortality rate, and the government and all sectors of society are probably not willing to see it.
In any case, the COVID-19 pandemic has literally claimed thousands of lives in Hong Kong, and no mortality calculation method can lighten their weight, and officials, experts and society must remember that they are not just numbers .
Rather than arguing over which calculation method can better reflect the actual death rate, the authorities and experts can come up with figures from the aforementioned formulas and list them. We should all continue to focus on first aid and emergency relief.
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