On March 20, a report in Nature, a top international academic journal, noted that preliminary studies suggest that recessive cases of the new coronavirus may account for about 60 percent of all infections. The main evidence for this conclusion is a paper published on March 6 by Wu Tangchun’s team at the School of Public Health of Huazhong University of Science and Technology on the medRxiv website, a preprint platform for medical papers. The paper analyzed data on 25,961 laboratory-confirmed cases of new coronary pneumonia from the Wuhan Municipal Health Commission’s statutory infectious disease reporting system as of Feb. 18. Based on these data, Wu Tangchun’s team estimated through modeling analysis that at least 59% of infections in Wuhan are undetected, which may include asymptomatic and mildly symptomatic cases. The paper argues that estimating undetected cases is important for ongoing surveillance and infection. Geometry of asymptomatic cases Several previous national and international studies have shown that the proportion of asymptomatic infected individuals may be much higher than expected. Asymptomatic infected patients include both occult patients who are always asymptomatic and latent patients. The so-called recessive patients refer to pathogens that invade the body and cause only a specific immune response, but do not cause or cause only minor tissue damage, and do not show any clinical signs and symptoms, or even biochemical changes, and can only be detected through laboratory tests. The WHO report on the joint China-WHO mission on novel coronavirus pneumonia (COVID-19), released after a mission to China from February 16 to 24, includes “risk factors for asymptomatic infection” and states that “asymptomatic infections have been reported, but most of the cases that are asymptomatic at the time of reporting are subsequently diagnosed. The report states that “asymptomatic infections have been reported, but most cases that are asymptomatic at the time of reporting will subsequently develop symptoms. The report notes that “the proportion of true asymptomatic infections is not known, but is relatively rare and not a major driver of transmission. However, the latest statistics and modeling suggest that the proportion of asymptomatic infections may be significantly underestimated. According to the Global Surveillance of 2019 Coronavirus Disease Caused by Novel 2019 Coronavirus Infection in Humans, published by WHO, “laboratory-confirmed infection with a new coronavirus is considered a confirmed case, regardless of the presence or absence of clinical signs and symptoms”. However, the criteria for confirmation of diagnosis in China are different. In the “Novel Coronavirus Pneumonia Prevention and Control Program (4th Edition)” issued by the National Health Commission, positive nucleic acid tests are divided into two categories: confirmed cases and asymptomatic infections, after which asymptomatic infections are no longer included in the confirmed list. In the fifth edition of the treatment protocol, which was updated on February 5, it was clearly stated for the first time that “asymptomatic infected persons may also be the source of infection. Korea has adopted the WHO definition of a confirmed case. In a March 16 press conference, CDC Director Jung Eun-kyung said, “Korea currently has significantly more asymptomatic cases than other countries, probably due to our extensive testing.” As of March 18, nearly 300,000 tests had been conducted in South Korea. Of the asymptomatic cases reported by the Korea CDC, more than 20 percent of the infected cases remained asymptomatic until they were discharged from the hospital. On February 13, the International Journal of Infectious Diseases received a paper from Japanese experts including epidemiologist Hiroshi Nishimura of Hokkaido University. This paper studied 565 Japanese citizens who were evacuated from Wuhan on a chartered flight and found that 13 of the evacuees were infected, of which four were asymptomatic infections, a rate of 30.8 percent. In this regard, Nishimura’s team estimates that less than half of those infected with the new coronavirus may be asymptomatic. “A study published in European Monitor on March 12 by Georgia State University mathematical epidemiologist Professor Gerardo Kaul showed that 634 people on board were positive as of February 20, and Kaul’s statistical modeling estimated that the proportion of asymptomatic infections was 17.9 percent. Recent studies have shown that asymptomatic or mildly symptomatic infections may be highly infectious. on March 8, a German research team published a study on the medical paper preprint platform medRxiv showing that some patients with neocoronavirus had higher levels of virus in throat swabs when their symptoms were mild early in the course of their illness. The paper, published March 19 in the New England Journal of Medicine by the Guangdong Provincial CDC, noted that 17 symptomatic patients identified in Guangdong Province had higher viral loads detected shortly after the onset of symptoms, and one asymptomatic patient had a similar viral load detected as a symptomatic patient, suggesting the potential for transmission in asymptomatic or mildly ill patients. Sampling urgently needed Wu Tangchun told China Newsweek that there may be 59 percent undetected cases of infection, which his team predicted based on the most conservative model and without actual epidemiological investigation. “Science is very rigorous, and what is possible cannot be said to be certain. There is no perfect spatial design of the model, so there must be a large sample to do the actual sampling to come up with regional differences and the potential number of hidden infections.” Wu Tangchun said. On this issue, back in mid-February, he and academician Wang Chen had suggested epidemiological sampling to the Hubei Provincial Epidemic Prevention Command and relevant authorities. The asymptomatic infections included latent patients who were not yet ill at the time of testing, as well as latent infections that never became ill after contracting the virus. Professor Jiang Qingwu, former dean of the School of Public Health at Fudan University and a member of the Chinese Society of Preventive Medicine’s New Coronary Pneumonia Prevention and Control Expert Group, said that many infectious diseases have latent infections, and at the same time, some latently infected people can become the source of infection. Because the hidden infected person with the virus will not be isolated and has a large range of activities, so its danger is greater. In the current situation, the model to determine the occult infection is a method, however, it should not be advocated because of the many assumptions of the model. He cautioned that with an infection as widespread as Wuhan, models should not be overly trusted, and the question of the number of occult infections must be answered by actual surveys. Jiang Qingwu explained that after the human body is infected with the virus, most patients produce antibodies, which is evidence that the virus is present in the human body. Thus, conducting antibody testing is a good way to confirm occult infections of new infectious diseases. In the Wuhan area, it is necessary to send professional epidemiological investigators to conduct antibody epidemiological sampling. Specifically, the survey can be divided into two parts, one for highly exposed populations such as close contacts of previously excluded confirmed cases, and the other for the general population. In theory, the larger the sample size, the better, according to Jiang Qingwu. A specific epidemiological survey, however, requires a series of assumptions to determine the sample size. Based on the current cumulative number of confirmed cases in Wuhan, a sample of at least 2,500 people must be made to reflect the overall situation. Jiang Qingwu pointed out that the data on occult infections is an important indicator to influence future decisions on whether the new crown pneumonia will make a comeback and what to do if it does. The authorities concerned can refer to the findings for the next stage of decision-making. “In the Wuhan area, the antibody sampling survey is fully operational. It is also something that should be done in Wuhan because there is no other region other than Wuhan where it can be done. Such a survey is meaningful to Wuhan and to the country, and as long as there is a possibility, it should be done even if the pots and pans are broken.” Jiang Qingwu stressed. On March 11, Wang Chen, academician of the Chinese Academy of Engineering and convener of the comprehensive expert group of the Hubei Provincial Prevention and Control Command, said in an interview with Xinhua News Agency that we are still far from having a deep grasp of the spread and pathogenicity pattern of the new coronavirus, and the epidemiological survey of nucleic acids and serum antibodies is the most critical scientific evidence for grasping the epidemiological pattern of this disease and is the most important basis for making scientific decisions on further prevention and control measures. Do a good epidemiological survey of nucleic acids and serum antibodies, is the immediate future to achieve scientific prevention and control must be completed, the most urgent key tasks. The importance of this survey, it should be said, is unparalleled, will have a direct impact on the prevention and control strategy, measures are professional. Wu Tangchun stressed again and again that the issue of occult infection is a very important scientific issue for both China and the world in the prevention and control of the epidemic, and should be given high priority. Content source: China News Weekly