Asymptomatic infection, invincible. Even at the end of March, China’s epidemic still exists a potential crisis, in addition to the increasing number of overseas imported cases, there are some sporadic local cases, but also let China’s epidemic prevention and control situation is still in a complex situation – which, easy to cause the spread of the virus asymptomatic infection, has become the focus of epidemic prevention and control.
In fact, for asymptomatic infections, our cognition may be too good.
Asymptomatic infections: infectious, but not the main source of infection
Before we know about asymptomatic infections, let’s take a look at how cunning the new coronavirus really is.
On March 27, in the preprinted magazine medRxiv, an article was published about a special case in which a moderate COVID-19 patient had a 49-day exclusion time for the virus.
Specifically, from January 25, the patient began to take fever, Chinese medicine and antiviral drugs after 1 week of self-infirmation, no other typical symptoms of COVID-19; However, the patient’s virus test sat positive for more than 30 days – the virus was removed after 51 days of serum treatment.
If not confirmed by a close contact, the case can be considered a typical asymptomatic infection after recovering from self-medication.
So, how exactly do you define asymptomatic infections?
According to the “New Coronary Virus Pneumonia Prevention and Control Program (Sixth Edition)” issued by the National Health and Reform Commission, asymptomatic infections refer to those who have no clinical symptoms (fever, cough, sore throat, etc.), respiratory tract and other specimens of new coronavirus pathogens or sero-specific IgM antibodies tested positive.
Liu Hening, former director of the PLA Respiratory Research Institute, believes that asymptomatic infections are divided into two situations:
First, the incubation period is still there after infection, but the incubation period will have symptoms, and thus develop into a confirmed case;
The second, from infection to recovery, has no symptoms from start to finish.
So how are asymptomatic infections generally found?
On February 14, Zeng Yixin, deputy director of the National Health and Care Commission, introduced the ways to find asymptomatic infections at a press conference, mainly from four sources:
Close contacts in new coronary pneumonia cases were found during the medical observation period;
In the investigation of the cluster outbreak, in the course of carrying out some active testing, asymptomatic infections may be found;
In the process of tracing the source of infection in new coronary pneumonia cases, asymptomatic infections may be found when active testing of exposed populations is carried out;
When actively detecting travel and residence history in areas where new coronary pneumonia cases continue to spread, asymptomatic infections may be found.
Simply put, the discovery of asymptomatic infections still relies on a process of investigation and nucleic acid testing that confirms that they carry the new coronavirus, but the process is not easy and greatly increases the covertness of the virus’s spread.
In addition, according to the New Coronary Virus Pneumonia Prevention and Control Program (Sixth Edition), suspected and confirmed cases require clinical performance, while asymptomatic infected persons, because of their non-clinical manifestations, need to be centrally isolated for 14 days and further accounting testing to determine – only asymptomatic infections during isolation symptoms, it is reported as a confirmed case and published.
It can be seen that asymptomatic infections are not confirmed cases.
But asymptomatic infections can also be a source of infection. For example, Liu Jiafa, secretary of the Hubei Provincial Center for Disease Control and Prevention, mentioned that asymptomatic infections may also become a source of infection, with a certain risk of transmission. But experts study, according to the general spread of infectious diseases and current data, asymptomatic infected people nucleic acid test positive, there is the possibility of excretion of pathogens, but because he did not cough, sneezing and other symptoms, the pathogen outside the body caused the probability of transmission is small.
In other words, asymptomatic infections may be the source of infection, but may not be the main source of transmission.
Academics are divided, but attention must be paid to asymptomatic infections
In fact, there are already many academic research results for asymptomatic infections.
As early as mid-February, the Epidemiology Unit of the China Center for Disease Control and Prevention (CDC) Emergency Response Mechanism for New Coronary Virus Pneumonia released a report describing and analyzing the epidemiological characteristics of a total of 723,000 cases reported in mainland China as of February 11, 2020.
It shows that out of 72,314 cases of neo-coronary pneumonia reported in the interior of China, there were 889 asymptomatic cases, accounting for 1.2% of all cases.
A modeling study published March 12 in the journal Eurosurvecle by Gerardo Chowell, an epidemiologist at Georgia State University, found that about 18 percent of the approximately 700 infected people on board the Diamond Princess had never developed symptoms.
On 20 March, Nature published an article entitled “Covertvirus corona infections can be new seedings.” The article argues that 30-60% of new coronary infections have no symptoms or mild symptoms, but their ability to spread the virus is not low, and these recessive infections may trigger a new outbreak.
Screenshot from Nature’s official website
To assess the extent of the hidden infection, researchers from China and the United States formed a research team to develop a model using clinical data from 26,000 laboratory confirmed cases from the Wuhan Municipal Health and Health Commission, the paper said.
As of February 18, 37,400 people in Wuhan had neo-coronaviruses — the majority of unreported cases were those with mild or no symptoms but could still be contagious, the team said in a preprinted paper published online March 6. Among them, Professor Yu Tangchun, Dean of the School of Public Health of Huazhong University of Science and Technology, said:
According to our most conservative estimates, at least 59% of those infected are untested and may be infected. This may explain why the virus is spreading so fast.
Screenshot from the official website of Huazhong University of Science and Technology
By late March, as the outbreak developed, asymptomatic infections received more and more attention.
Among them, at the March 27 seminar on “Basic Research and Prevention practices on virus evolution, evolution and transmission (from SARS to COVID-19),” Zhang Wenhong, Director of the Infection Department of Huashan Hospital affiliated with Fudan University and Head of the Senior Expert Group of the Shanghai Expert Group on New Crown Pneumonia, said:
The new coronavirus is probably the most difficult virus to deal with in human history, it is very powerful transmission, although the young people infected after the serious ity rate is very low, but the overall serious ity rate is significantly higher than influenza. And the existence of neo-coronavirus asymptomatic infected people, they have no clinical symptoms, pathogen test ingressis test is positive, to the epidemic prevention and control has brought challenges.
Zhang Wenhong said that asymptomatic infection is China into the epidemic prevention and control “second half” of a kind of important monitoring targets.
In response to the infectious ness of asymptomatic infections of new coronary pneumonia, a paper entitled “Epidemiological characteristics of infection among close contacts of new coronavirus pneumonia in Ningbo City” published by Chen Wei and others of the Institute of Infectious Disease Prevention and Control of the Center for Disease Control and Prevention of the Center for The Study of The Center for The Study of The Chinese Journal of Epidemiology, has previously published a paper on the infectious characteristics of the asymptomatic infections of the new coronavirus pneumonia in Ningbo City. A preliminary analysis is given.
This paper included 157 confirmed cases and 30 asymptomatic infections in Ningbo City, and they identified a total of 2,147 close contacts, of which the number of close contacts was at least 0, the maximum number of cases was 111, and an average of 11.5 cases. Of the 2147 close contacts, a total of 110 developed as confirmed cases, 22 were asymptomatic, and the total infection rate of close contacts was 6.15%.
As a result, the paper yields data: the infection rate of close contacts in confirmed cases is 6.3%, and the infection rate among close contacts of asymptomatic infections is 4.11% – although it is important to note that the difference in infection rates between the two is not statistically significant.
However, with regard to asymptomatic infections, Academician Zhong Nanshan’s views are more widespread, he said in an interview:
In general, asymptomatic infections are high in people who are in close contact with them. But the number of new confirmed cases of new coronary pneumonia in China has not only not risen, but is declining… This can be explained: China does not have a large number of asymptomatic infections. There are no specific figures on the situation of asymptomatic infections in China, and detailed and professional research is needed in the coming months.
The good news is that the prevention and treatment of asymptomatic infections has attracted great attention at the national level.
On March 26, the Central Leading Group for Response to the Outbreak of New Coronary Pneumonia held a meeting in which it said that no matter which way asymptomatic infections were detected, a clear scientific prevention and treatment programmeshould should be developed in accordance with medical rules to resolutely curb the possible formation of new viral infections and the spread of the epidemic.
However, in the last two days, the recent new local cases are associated with asymptomatic infections;
After all, as Professor Zhang Wenhong says, the new coronavirus is probably the most difficult virus to deal with in human history.