Research: Asymptomatic transmission does occur in COVID-19! In the face of community epidemic, it is necessary to evaluate its threat.

A few days ago, the research team led by Hiroshi Nishiura, a professor of infectious disease epidemiology at Hokkaido University, published the research results [1] (note: as of February 13, the research is still under peer review and has not been officially published), and estimated the novel coronavirus in 20 19 (coronavirus pneumonia-/). Because this research has aroused widespread concern in the media, this paper will explain and comment on this research.

Take novel coronavirus (coronavirus pneumonia-19) in 20 19 as an example. According to the estimation of the teams of the United States [2], the Netherlands [3] and China [4], the average symptom incubation period is about 5.2 days (10 1 case) and 6. Important epidemiological characteristics of emerging infectious diseases

When we are infected by pathogens, the pathogens will multiply in the body for a period of time and react with the human immune system, and then the symptoms will begin to appear. The time interval from infection to symptoms is called incubation period. Take novel coronavirus (coronavirus pneumonia-19) in 20 19 as an example. According to the estimation of the teams of the United States [2], the Netherlands [3] and China [4], the average symptom incubation period is about 5.2 days (10 1 case) and 6. In addition, another important information for understanding the transmission characteristics of new infectious diseases is the serial interval, which refers to the interval between the onset date of symptoms of infected people and infected people in two cases of mutual transmission. Assuming that patient B in figure 1 is infected by patient A, the generation interval is the time interval from the first symptom of patient A to the first symptom of patient B. The calculation of the generation interval depends on epidemiological investigation to determine the transmission relationship between patients, so it is difficult to collect data. Take this epidemic as an example. Although there are a large number of human-to-human cases in China, the investigation of the epidemic is not enough to collect detailed epidemic information. In a study published earlier by the China Municipal Bureau of Disease Control [3], only 6 out of 425 reported cases had enough information to estimate the interval (about 7.5 days on average). Although the epidemic investigation in other countries has been completed, there are still few cases of human-to-human transmission, and most of them are cases of immigrants from abroad, so it is impossible to calculate the generation interval. At present, only two pairs of cases of primary transmission have been found in Taiwan Province province, and the generation interval is 1 day and 6 days respectively.

(Photo courtesy of Professor Lin Xianhe, full-time researcher Wu Dazhou and full-time researcher Wu Chuying from the School of Public Health of National Taiwan University) We draw the time axes of "infection" and "onset" of infected people and infected people respectively. In the first scenario, if it can only be transmitted to others after symptoms appear, then we would expect that the generation interval of onset will be longer than the incubation period of symptoms (Figure 1 first half); In the second scenario, the patient is transmitted to the next person before the onset, and the interval between generations of onset will be less than the incubation period of symptoms (the lower part of the figure). Therefore, the possibility of asymptomatic transmission can be judged by comparing the relative length and generation interval of symptom incubation period.