On January 15, Haidian District reported the first local case of Omicron in Beijing; on January 17, the disease control department announced the traceability progress: it may be related to an international express.
Although "human-to-human" is established from a professional point of view, it is mostly related to the cold chain. For example, in the epidemic in Qingdao in 2020, live viruses on cold-chain goods were found, which became strong evidence that "human-to-human transmission".
However, there is no example of ordinary express mail that is not in the cold chain infecting people.
Why do tracers focus on items?
How to distinguish between "human-to-human transmission" and "case-contaminated items"?
On January 18, Jiang Chu, director of the Haidian District Center for Disease Control and Prevention, accepted an exclusive interview with a reporter from the Beijing News to reveal the source of the trace.
The mother of the first case provided a positive express clue
Beijing News: When the city CDC reported the traceability of positive shipments, the outside world was surprised.
Generally, traceability is more inclined to look for people. How can I pay attention to express shipments this time?
Jiang Chu: In fact, this matter did not come out of the mouth of the case.
During the epidemiological process, we asked whether the case had come into contact with overseas personnel or high-risk groups, and she definitely said no.
But her mother was alert, saying that she had taken mail from abroad, which gave us clues.
From our general understanding, the probability of material transmission is not high.
However, the experts in the city's disease control were very sensitive and gave us guidance. They were very resolute in saying that they would be traced, and we would further trace the source of the items.
This is the first critical link.
Ordinary express items are thrown away after dismantling and will not be preserved.
The unit where the case was located kept things well, date-coded and neatly organized, and although the volume of mail was large, it was not cluttered, so we quickly found the originals.
This is the second key link.
This email has been out for a long time, and the virus was still detected during the test. This is the third.
Subsequently, similar viruses were found from other emails from the same source, and they were highly homologous to the mutant strains in Canada and the United States.
This is the fourth key link.
In this process of tracing the source, if there is one link in the middle, the clue will be broken, and the follow-up may have to be searched endlessly.
Beijing News: There has been some research evidence for human-to-human transmission, but it is generally cold chain transmission. There is no example of ordinary express delivery that is not cold chain, and the virus has limited viability at room temperature.
In this inference, has a live virus been cultured or the virus was genetically sequenced?
How was it established?
Jiang Chu: I have never heard of ordinary express mail.
The reason why the cold chain can spread is because the fan will start as soon as the temperature in the cold storage changes, causing a large airflow, and the virus stored at low temperature is blown up to form aerosol. In the case of a large amount, it may cause infection.
Genetic sequencing is definitely going to be done.
But viruses can replicate in large numbers only in organisms, and cannot reproduce in the environment, but only decay.
In the case of low viral load, the effect of sequencing may not be good, this is one of them.
Second, even if the sequencing results can be compared, one of the most critical causal questions must be answered: whether the virus on the email caused the human infection, or did the human infection contaminate the email.
The probability of the former is very low, the latter is very easy.
How to distinguish the order? The reasoning logic is as follows: Viruses are found in people and objects that have been in contact with them, and the two are almost certainly related; where did the emails come from?
This one is not the only one from the same source. In other international emails sent from the same region, we detected similar viruses, which means that the emails were "infected" first.
In addition, according to the sequencing of the mutant strains detected in the case, the analysis of the domestic database is not correct, and the case has not been in contact with overseas or high-risk groups, the probability of physical transmission is higher; The sequence of the strain was highly consistent with the strain detected in the case, which further suggested the source, and finally formed the traceability inference of the disease control department.
The Beijing News: The amount of virus on the surface of the object is relatively low, and the virus is easily inactivated. How could it be possible for non-cold chain express mail to pass from person to person?
Jiang Chu: According to our analysis, it may have happened under a special circumstance.
For example, whether there is a large source of pollution, causing serious contamination of the mail, it is well sealed during transportation, and it is winter, and the temperature is conducive to the survival of the virus.
On the other hand, when receiving express mail indoors, few people wear masks and pay special attention to hand hygiene. It is possible that the cases did not wash their hands and wear masks during the process of unpacking the mail, and eventually became infected.
Beijing News: How can we "look directly" at express mail in the future?
Jiang Chu: We need to be more vigilant, and there is no need to panic.
Even if there is a single case, the probability of this is still very small.
Try to accept as few express items from high-risk areas as possible, protect yourself during the pickup and disassembly process, and seek medical attention in a timely and correct manner if suspicious symptoms occur.
But hygiene habits are simple to say, but it takes more effort to actually implement them in daily life.
Hopefully this Omicron outbreak will be clearly contained in the next week or so
Beijing News: Will the traceability of the epidemic continue?
Is it over yet?
Jiang Chu: We will further track international mails. This batch of mails may have been distributed to dozens of points. We need to test them. If more samples are found, statistical analysis can be carried out, and the probability will be higher. Manage people to prevent similar situations from happening again.
The Beijing News: A new case announced on the 18th is not under the secret control. What is the situation?
Jiang Chu: This case, as a high-risk group isolated at home, belongs to the infection of non-direct contact.
The so-called close contact refers to eating, living, and close contact with the infected person, especially meeting, shaking hands, and eating when they are sick.
The two people did not meet, but the latter went to the former's office. In winter, the indoor insulation and ventilation were not particularly good, which may have caused indirect infection.
In addition, this may also have something to do with the characteristics of Omicron.
Omicron reproduces more in the upper respiratory tract, and people are more likely to excrete the virus through breathing, talking, and coughing, resulting in aerosol transmission.
Beijing News: It was the first time that you played against Omikron, and what features did you find?
Jiang Chu: The viability and spread of the virus is indeed beyond cognition.
In addition, the incubation period of Omicron is also much shorter.
The general incubation period of the new coronavirus is about 7 days, and the longest can reach 14 days. The incubation period of the first case this time is only about 3 days.
Beijing News: Will the prevention and control strategy change?
Jiang Chu: The strategy of prevention and control is to be fast, to conduct investigations as soon as possible, to identify the transmission chain, and to control the close contact, high-risk groups, and risk points as soon as possible; the time division of traceability and risk groups should also be adjusted, which may be relatively short.
In general, for Omicron, professional departments must continue to track and research to provide more basis for prevention and control strategies and methods.
Beijing News: What is the degree of control of the epidemic in Haidian?
Jiang Chu: At the beginning, because the transmission chain was unclear, the scope of control was relatively large. Through large-scale nucleic acid testing, the trajectories and places involved in the cases were investigated; through epidemiological investigation and gene sequencing, the transmission was quickly locked. The direction, the transmission chain is clear, and the routine characteristics of the new cases in the later period are reviewed, and the close connection and point can be more accurately delineated, and the corresponding management and control can be carried out to reduce the inconvenience to life and the waste of social resources, and the efficiency and effect are improved. Very obvious.
It was the first time I met a person from a non-cold-chain material, and it was also the first time that Omikron met. We were very cautious, and the scope of control was appropriately expanded. Part of the people who were tested for nucleic acid was to trace the source, and part of it was to detect the risk of the crowd.
Beijing News: How to judge the situation of this epidemic?
Jiang Chu: According to the current situation, it should be controllable, and I hope it will be clearly controlled in the next week or so.
Generally speaking, when dealing with an epidemic, the disease control system finds out the biggest risks and finds clues in about 24 hours, and the later work is easy to do; if you don’t understand it in the first 24 hours, the later stage may mean a huge amount of work, and tracing the source is like looking for a needle in a haystack.
Preliminary adjustment is very important.
This time, the rapid control was achieved under the guidance and help of the city's CDC, as well as the cooperation and support of the district CDCs.
Beijing News: What are the next steps for epidemic prevention and control?
Jiang Chu: We have informed some communities to strengthen the monitoring of symptoms and report symptoms in a timely manner. The community will provide citizens with nucleic acid testing or prevention and control guidance according to the situation.
Winter is the season of high incidence of respiratory diseases, and there must be some control over gatherings, gatherings, and large-scale events.
As for the subordinate administrators, we must be prepared to respond at any time; the citizens have cooperated with our work very much, and we hope that everyone will further strengthen self-protection, reduce gatherings, and get vaccinated against the new crown in time.
Beijing News reporter Dai Xuan