因為有不少朋友建議我，將日前臉書上“武漢肺炎發生率與致死率的國際比較”一文翻譯成英文，所以，就以英文版再次和大家分享，也謝謝大家的批評指教。
International Comparison of Incidence and Mortality Rates of COVID-19
In the statistics of the COVID-19 collected and published by the World Health Organization (WHO), only the numbers of confirmed cases and deaths of COVID-19 of affected countries are available, without taking the population of each country into consideration. It will result in a biased assessment of the COVID-19 risk for each country.
Better data for international comparison is incidence rates, which refer to the number of confirmed COVID-19 cases (numerator) divided by the number of the population (denominator) of a given country. As shown in Table 1. the incidence rate per 100,000 population was highest in Italy, Korean, Iran, and China (>5.0 per 100,000) and much lower in Japan, US and Taiwan (<0.5 per 100,000).
The number of confirmed COVID-19 cases in each country is not only related to its population but also dependent on the coverage rate of the COVID-19 virus test. The confirmed case number and incidence rate are relatively low for those countries where only the severe cases were tested for COVID-19 virus; and they are much higher for countries where severe, moderate and mild cases were tested for the virus.
Once a country changes its policy of virus testing, for example of testing only those who are seriously ill, the number of the confirmed cases and incidence rate will drop sharply in a short period of time, but its case fatality rate will rise accordingly.
The case fatality rate is the proportion (percentage) of confirmed COVID-19 cases who died from the disease. Its numerator is the number of confirmed cases who died from the disease, and its denominator is the total number of confirmed cases. It is for sure that the case fatality rate will be higher if the analysis is limited to severe cases, and it will drop dramatically if the analysis also includes moderate and mild cases.
As shown in Table 2, the case fatality rates are the same for severe (5%), moderate (0.5%) and mild (0.1%) COVID-19 confirmed cases in countries A, B, and C are the same, but
the overall case fatality rates per 1,000 confirmed cases are significantly different among the country A, where only test the severe cases (41 per 1,000), country B where both severe and moderate cases are tested (14 per 1,000), and country C where test all severe, moderate and mild cases (8 per 1,000).
Among the countries with more than 1,000 confirmed cases in Table 1, the overall case-fatality rates in Italy, China and Iran were all exceeded 3.5%. Obviously, the severe cases account for a relatively large proportion of confirmed cases. The overall case-fatality rate for South Korea and Germany was only 0.8% and 0.1%, respectively, where the moderate and mild cases account for a relatively large proportion.
When we see a rapid decline in the number of confirmed cases with a soared case fatality rate, we must first pay attention to the change in the country's virus testing strategy. The Director-General of WHO recently stated that all countries should be cautious for the case fatality rate of COVID-19 is rising! The conclusion that the Director-General was biasedly made without taking the change in the virus testing strategy into consideration. He made the matter worse by causing unnecessary panic!
In addition to the virus-detection strategy, some other factors such as age, chronic disease status, and quality of medical care also affect the case fatality rate. For examples, the fatality rate will be low if the patients in the hospital for isolation treatment are mostly young people, without chronic disease, and receiving good cares. If most patients are old, with chronic disease, and receiving inadequate cares due to limited hospital resources and manpower, the case fatality rate will become high.
