How large is the asymptomatic infection population in China

• by EVOMT
• 2020-04-13

With the gradual improvement of the situation of the COVID-19 in China, asymptomatic infected people have become the focus of attention from all walks of life. For this reason, the government has also issued management norms for asymptomatic infected people.

On April 8, in response to the joint prevention and control mechanism of the novel coronavirus pneumonia epidemic, the State Council issued the Management Specifications for Asymptomatic COVID-19 Infected Persons, reiterating that asymptomatic infected persons are infectious and have transmission risks. It is required to strengthen the monitoring and detection of asymptomatic infections and standardize the reporting of asymptomatic infections. Medical and health institutions at all levels and types should report asymptomatic infections through the network within 2 hours.

The Management Specification also explicitly states that the management of asymptomatic infected persons should be strengthened, and asymptomatic infected persons should be subject to centralized medical observation for 14 days, while close contacts should also be subject to centralized medical observation for 14 days.

According to the Management Specifications, asymptomatic COVID-19 infected persons (hereinafter referred to as asymptomatic infected persons) refer to those who have no relevant clinical manifestations, such as fever, cough, sore throat and other symptoms and signs that can be perceived or recognized clinically, but whose respiratory tract and other specimens are positive in the pathogenic test of COVID-19.

There are two conditions for asymptomatic infections: first, after 14 days of isolation medical observation, there are no symptoms and signs that can be perceived or clinically recognized; The second is in the incubation period; ldquo; Asymptomatic infection; rdquo; Status.

So, how large is the current population of asymptomatic infected people in China, what is the potential for asymptomatic infected people to transmit the virus, and how is the current prevention and control in China?

How many asymptomatic infected people in China are in the outbreak period of the COVID-19 epidemic. The asymptomatic infected people are not the key population for prevention and control. China has not released relevant data.

Until March 31, the Disease Prevention and Control Bureau of the National Health Commission disclosed in the Q&A on the Prevention and Control of Asymptomatic novel coronavirus Infected Persons that, as of 24:00 on March 30, 2020, there were 1541 asymptomatic infected persons under medical observation, including 205 imported cases.

Since then, China has begun to disclose the number of asymptomatic infections every day.

According to the official website of the National Health Commission, as of 24:00 on April 8th, 31 provinces (autonomous regions, municipalities directly under the Central Government) and the Xinjiang Production and Construction Corps reported 56 new cases of asymptomatic infections, including 28 imported asymptomatic infections; 15 cases were confirmed on the same day (15 cases were imported from overseas); 32 cases were removed from medical observation on the same day (7 cases were imported from overseas); 1104 asymptomatic infections are still under medical observation (364 cases imported from overseas).

Of these 1104 cases, Hubei ranked first with a total of 674 cases, while most asymptomatic infections in other provinces were imported from abroad. Among them, the top three were 154 cases from Heilongjiang (all imported from abroad), 76 cases from Guangdong (including about 46 imported from abroad), and 50 cases from Zhejiang (including 41 imported from abroad). Beijing, Shanghai, Jiangsu, Inner Mongolia, Xinjiang, Tibet, and Ningxia all had 0 cases.

It should be noted that these 1104 cases are only the number of asymptomatic infections currently under medical observation in China.

Wu Zunyou, the chief epidemiologist of the China Center for Disease Control and Prevention, mentioned at the press conference of the Joint Prevention and Control Mechanism of the State Council on April 2 that a study conducted by the Ningbo Center for Disease Control and Prevention found that, from a group level perspective, the proportion of cases transmitted by asymptomatic infected persons in the total number of patients was only 4.4%, less than 5%. This is a local study in Ningbo.

Many experts also tend to believe that the proportion of asymptomatic infections occurring throughout the epidemic will be higher if they are counted.

In the afternoon of April 8, the Embassy in Bangladesh and the Shanghai Municipal Foreign Affairs Office jointly organized a video link meeting to fight against the COVID-19. Zhang Wenhong, the leader of the medical treatment expert group of COVID-19 in Shanghai and the director of the Infection Department of Huashan Hospital affiliated to Fudan University, said at the meeting that the proportion of asymptomatic COVID-19 infected people was 36% - 38%.

On the previous March 6, the team of Wu Tangchun from the School of Public Health of Huazhong University of Science and Technology published a paper on medRxiv, a medical paper preprint platform, to analyze the data of 25961 laboratory confirmed cases of COVID-19 in the legal infectious disease reporting system of Wuhan Health Commission as of February 18. Based on these data, Wu Tangchun's team estimated through modeling analysis that at least 59% of infections in Wuhan are undetected, possibly including asymptomatic and mild cases.

However, Wu Tangchun also stated that there may be 59% of undetected infections, which his team predicted based on the most conservative model and did not conduct actual epidemiological investigations.

Jiang Qingwu, the former dean of the School of Public Health of Fudan University and a member of the COVID-19 Prevention and Control Expert Group of the Chinese Preventive Medicine Association, reminded in an interview with China Newsweek that the model should not be over trusted for a wide range of infections like Wuhan, and the number of recessive infections must be answered through actual surveys.

According to the news on the website of the National Health Commission on April 10th, as of 24:00 on April 9th, according to reports from 31 provinces (autonomous regions, municipalities directly under the Central Government) and Xinjiang Production and Construction Corps, there are currently 1116 confirmed cases (including 144 severe cases), 77455 discharged cases have been cured, 3336 deaths have been reported, and 81907 confirmed cases have been reported. A total of 717378 close contacts have been traced, and 11176 close contacts are still under medical observation. In 31 provinces (autonomous regions, municipalities directly under the Central Government) and Xinjiang Production and Construction Corps, 1097 asymptomatic infections are still under medical observation (349 cases imported from abroad).

Cartography: Pengpai Journalist Yao Xiaolan

Transmission potential of asymptomatic infected persons The Prevention and Control Plan for novel coronavirus Pneumonia (Sixth Edition) points out that asymptomatic infected persons can also become a source of infection. Therefore, there is a certain transmission risk.

The World Health Organization believes that:; ldquo; Based on existing data, novel coronavirus is mainly transmitted by patients with symptoms& rdquo;， Therefore, asymptomatic infections may not be the main source of transmission.

What is the transmission potential of asymptomatic infections?

In the Q&A on the Prevention and Control of Asymptomatic novel coronavirus Infections, the Disease Prevention and Control Bureau of the National Health Commission said that according to the monitoring data of close contacts carried out by the country and some provinces, the close contacts of asymptomatic infected people have a second generation of cases. Epidemiological investigation found that individual clusters of outbreaks caused by asymptomatic infected people, Studies with a small sample size have shown that there is no significant difference between the viral load in respiratory tract samples from asymptomatic infected individuals and confirmed cases. Based on current monitoring and research, asymptomatic infected individuals are infectious, but further scientific research is needed on the length of their infectious period, infectious strength, and mode of transmission. Some experts believe that given that the respiratory tract samples of asymptomatic infected individuals can detect pathogenic nucleic acids, but due to the absence of clinical symptoms such as coughing and sneezing, the chances of transmission caused by pathogen excretion outside the body are relatively less than those of confirmed cases.

In a report by the Health Times on April 8th, Academician Zhang Boli believed that asymptomatic infections generally do not cause a major outbreak. He cited a recent study by the Ningbo Center for Disease Control and Prevention that an average of 3 patients can be transmitted per confirmed patient, and less than 1 patient can be transmitted per asymptomatic infected person. The infectivity of asymptomatic infected persons is equivalent to one-third of the confirmed cases& amp; ldquo; With the measures currently taken in China, asymptomatic infections can be detected and controlled in a timely manner, and the possibility of epidemics caused by asymptomatic infections is relatively small. Asymptomatic symptoms are often not true asymptomatic, but they are mild and do not attract attention. Therefore, in the case of an epidemic, everyone in every corner should pay attention to their physical condition, observe any discomfort, and be sure to go to the hospital for examination if necessary& amp; rdquo;

In addition, according to current epidemic prevention and control measures in China, the risk of transmission and diffusion of asymptomatic infected persons is also small.

Wu Zunyou mentioned at the press conference of the Joint Prevention and Control Mechanism of the State Council on April 2 that all asymptomatic infected persons must have had a history of contact with a confirmed patient, or have been to an epidemic area where the epidemic is currently occurring. For areas where the epidemic has occurred but the confirmed cases have been cleared for more than two weeks, asymptomatic infected persons will not suddenly appear without reason. Our current measures should be able to detect and control asymptomatic infections in a timely manner. The likelihood of an epidemic caused by asymptomatic infections is very low and will not cause social diffusion.

How to prevent and control asymptomatic infections in China Today, the State Council has issued the "Management Specification for Asymptomatic COVID-19 Infected Persons" to further standardize the discovery, reporting and management of asymptomatic infected persons in response to the joint prevention and control mechanism of the novel coronavirus pneumonia epidemic.

Specifically, in terms of monitoring and detection: first, active detection of close contacts of COVID-19 cases during medical observation; The second is active detection in aggregated epidemic investigation; Third, active detection of exposed people in the process of tracking the infectious source of COVID-19 cases; Fourth, the active detection of some people with a history of living in areas where COVID-19 cases continue to spread at home and abroad; The fifth is related personnel found in epidemiological investigations and opportunistic screening.

In terms of reporting, the "Management Code" requires that medical and health institutions at all levels and various types should conduct direct online reporting within 2 hours after discovering asymptomatic infections.

In terms of management, the "Management Code" clearly states that asymptomatic infected persons should be subject to centralized medical observation for 14 days. During this period, patients with clinical symptoms and signs related to COVID-19 were transferred to confirmed cases. Centralized medical observation can be cancelled if the patient has been under centralized medical observation for 14 days and has tested negative for nucleic acid in two consecutive samples (the sampling time is at least 24 hours apart). If the nucleic acid test is still positive and there are no clinical symptoms, it is necessary to continue centralized medical observation. Close contacts of asymptomatic infected persons should be subject to intensive medical observation for 14 days. Asymptomatic infected persons who have been released from centralized medical observation should continue to undergo 14 days of medical observation and follow-up. Visit a designated hospital for follow-up visits in the second and fourth weeks after the release of centralized medical observation to promptly understand their health status.

The difficulty of asymptomatic prevention and control lies in the fact that asymptomatic infected persons have no obvious symptoms and signs, and are difficult to detect in the population, as well as preventing the transmission caused by them. Those with mild or atypical symptoms may think that they are not infected with COVID-19, do not take the initiative to go to medical institutions, and are difficult to be found in daily diagnosis and treatment.

At a press conference held by the Joint Prevention and Control Mechanism of the State Council on April 2, Wang Bin, the supervisor of the National Health Commission's Bureau of Disease Control, introduced that the current requirements for reporting asymptomatic infections, epidemiological investigations, and management of close contacts are basically consistent with the confirmed cases. In order to further strengthen the monitoring of asymptomatic infected persons, we need to further strengthen targeted screening efforts, further expanding the scope of monitoring to already detected cases and close contacts of asymptomatic infected persons, clustered epidemics, and active screening in key areas and key populations. At the same time, we will also play the monitoring role of community and fever clinics, track and manage infectious sources according to case clues, improve the sensitivity of monitoring, timely detect asymptomatic infections, and timely take centralized isolation measures. Epidemiological investigations should be carried out in a timely manner on asymptomatic infected persons, their sources should be identified, and relevant information should be publicly and transparently released.

At a video link meeting on April 8, Zhang Wenhong, the leader of the medical treatment expert group of COVID-19 in Shanghai and director of the Infection Department of Huashan Hospital affiliated to Fudan University, judged that asymptomatic patients would never exist in isolation, and all asymptomatic patients must exist with symptomatic patients at the same time,& ldquo; "You can wait and see. If there is no significant increase in confirmed cases and asymptomatic infections in China in the next 2-4 weeks, you can stop thinking about them.". Everyone will also ask if there are any patients who have become chronically infected with the virus, and there is currently no evidence to prove that this is a chronic viral infection& amp; rdquo;< img alt="" src="/staticfile/upload/image/200413/1-200413144T5437.jpg" style="width: 952px; height: 1564px;"/>

笔记