Why keep your eyes on an item? Demystifying the origin of the Beijing positive express: The mother of the first case was alert and provided key clues

On January 15, Haidian District reported the first local case of Aomi Kerong in Beijing; on January 17, the CDC announced the traceability progress: or related to an international express shipment.

Although "material-to-human" is established from a professional point of view, it is mostly related to the cold chain, such as the outbreak in Qingdao in 2020, which found a live virus on cold chain goods, which has become a strong evidence of "material transmission to people". However, there are no examples of non-cold chain ordinary express mail transmission to humans.

Why do tracers lock their eyes on items? And how to distinguish between "material transmission to person" and "case contaminant product"? On January 18, Jiang Chu, director of the Haidian District Center for Disease Control and Prevention, was interviewed by a reporter from the Beijing News to reveal the origin of this traceability.

The mother of the first case provides a positive express clue

Beijing News: When the municipal disease control reported the traceability of positive express mail, the outside world was still relatively unexpected. General traceability is more inclined to find from people, how to pay attention to express mail this time?

Jiang Chu: This incident did not actually come out of the mouth of the case. During the circulation process, we asked whether the case had been in contact with people from abroad or high-risk groups, and she said with certainty that she did not. But her mother was alert, saying she had taken mail from abroad, which provided us with clues.

From our general understanding, the probability of material transmission is not high. But the experts of the municipal disease control are very sensitive, give us guidance, very firmly say that we want to trace, we further trace the source of the item. This is the first key link.

General express mail, after disassembly, will be thrown away, will not be saved. The unit where the case was located kept things very well, and they were neatly arranged according to the date code, although the mail volume was large, but it was not messed up, so we quickly found the original. This is the second key link.

This email was put on for a long time, and the virus was detected when it was detected, which is the third. Subsequently, similar viruses were found in other emails of the same source, and they were highly homologous to the variants in the direction of Canada and the United States. This is the fourth key link.

This traceability process, but where there is a link in the middle, the clue is broken, and the follow-up may have to search endlessly.

Beijing News: There is some research evidence in the past, but it is generally cold chain transmission, non-cold chain ordinary express delivery has no examples, and the virus has limited vitality in the normal temperature environment. In this retrospective inference, has it been cultured to live viruses or genetic sequencing of viruses? How was it established?

Jiang Chu: Ordinary express mail generations have really not heard of it much. The cold chain can achieve transmission because as soon as the temperature in the general cold storage changes, the fan starts, causing a large airflow, and the virus stored at low temperatures is blown up to form an aerosol, and in the case of a large amount, it may cause infection.

Gene sequencing is definitely done. But viruses can only replicate in large quantities in living organisms, cannot reproduce in the environment, and only decay. In the case of low viral volume, the effect of sequencing may not be good, which is one of them. Second, even if the sequencing results come out, they can be compared, and one of the most critical causal questions must be answered: whether it is the virus on the email that causes the person to be infected, or whether the person infects the mail after it contaminates the mail. The probability of the former is low, the latter is easy.

How to distinguish the order, the reasoning logic is like this: people, the objects that have been touched have found viruses, the two are almost certainly related; where did the email come from? This will not be the only one from the same source, but in other international emails sent from the same region, we have detected similar viruses, which indicates that the mail is "infected" before.

In addition, according to the sequencing of the mutant strain detected in the case and the analysis of the domestic database, it is not correct, and the case has not been in contact with overseas or high-risk people, and the probability of material transmission is higher; the strain circulating in the area where the email is sent is highly consistent with the sequence of the strain detected in the case, which further prompts the source, and finally forms the traceability inference of the disease control department.

Beijing News: The amount of virus on the surface of the object is relatively low, the virus is easy to inactivate, how may the non-cold chain express mail transmission occur?

Jiang Chu: We analyze that it may have happened under a special circumstance. For example, whether there is a large source of pollution, causing serious pollution of mail, the transport is well sealed, and it is winter, and the temperature is conducive to the survival of the virus. On the other hand, few people wear masks and pay special attention to hand hygiene when receiving express mail every day, and it is possible that cases do not wash their hands and wear masks during the process of unpacking mail, and eventually become infected.

Beijing News: How can we "look directly" at the express mail in the future?

Jiang Chu: We need to be vigilant, and there is no need to panic too much. Even if there are individual cases, this probability is still very small. Try to receive less express mail from high-risk areas, do a good job of self-protection during the process of picking up and disassembling, and seek medical treatment in time and correctly if suspicious symptoms occur. But hygiene habits are simple to say, and if they are really implemented in daily life, they still need to be strengthened.

Hopefully, the Opmikron outbreak will be significantly under control in the coming week or so

Beijing News: Will the traceability of the epidemic continue? Or is it over?

Jiang Chu: We will further track international mail, this batch of mail may be diverged to dozens of points, we want to test, if more samples are found, statistical analysis can be carried out, the probability will be greater; but also to manage the personnel, to avoid similar situations from happening again.

Beijing News: A new case announced on the 18th is not in the close control, what is the situation?

Jiang Chu: This case, as a high-risk group in home isolation, is an infection of indirect contact.

The so-called close contacts refer to eating and living with infected people, living together, and having close contact, especially meeting, shaking hands, and eating when the disease is onset.

The two men did not meet, but the latter went to the former's office, and the indoor heat preservation and ventilation were not particularly good in winter, which may have caused indirect infection.

In addition, this may also be related to the characteristics of Omikeron. Omikeron reproduces more in the upper respiratory tract, and people are more likely to excrete the virus through breathing, talking, and coughing, causing aerosol transmission.

Beijing News: The first time I fought with Aomi Kerong, what other characteristics did you find?

Jiang Chu: The vitality and spread of the virus is indeed beyond cognition. In addition, the incubation period of Omikeron is also much shorter. The general incubation period of the new crown virus is about 7 days, the longest can reach 14 days, and the incubation period of the first case is only about 3 days.

Beijing News: Do prevention and control strategies change?

Jiang Chu: The strategy of prevention and control is to be fast, as soon as possible to adjust and find out the transmission chain, and to control the close connection, high-risk groups and risk points as soon as possible; for the traceability and division of the time of the risk group, it should also be adjusted, which may be relatively short.

In general, for Omi kerong, the professional department must continue to track and study to provide more basis for prevention and control strategies and means.

Beijing News: How well is the epidemic in Haidian controlled?

Jiang Chu: At the beginning, due to the unclear transmission chain, the scope of control was relatively large, through large-scale nucleic acid detection, the trajectory and place involved in the case were checked; through flow regulation and gene sequencing, the direction of transmission was quickly locked, the transmission chain was clear, and the contact and incidence of new cases in the later period were in line with conventional characteristics, and the close connection and point could be more accurately demarcated, and the corresponding control could be carried out to reduce the inconvenience caused to life and the waste of social resources, and the efficiency and effect were very obvious.

Non-cold chain inheritance of the first time to see, Omicron is also the first time to fight, we are very careful, the scope of control or appropriately expanded some, nucleic acid testing of the population, part of the purpose of traceability, part of the risk of touching the population.

Beijing News: How to judge the situation of this epidemic?

Jiang Chu: According to the current situation, it should be controllable, and I hope to be significantly controlled in the next week or so.

Generally speaking, when dealing with the epidemic, the disease control system can find out the biggest risk and identify clues in about 24 hours, and the later work is easy to do; the first 24 hours of investigation cannot be understood, and the later stage may mean a huge amount of work, and the traceability is like finding a needle in a haystack. Upfront flow tone is very important.

The rapid control this time was completed under the guidance and help of the Municipal Disease Control and the cooperation and support of the CDC of various districts.

Beijing News: What is the next step of epidemic prevention and control?

Jiang Chu: We have notified some communities to strengthen the monitoring of symptoms, and the symptoms must be reported in time, and the community will provide nucleic acid testing or prevention and control guidance to the public according to the situation. Winter is the season of high incidence of respiratory diseases, and there is still a certain degree of control over gatherings, gatherings, and large-scale activities. From the perspective of territorial administrators, we must be prepared to respond at any time; the public has been very cooperative with our work, and we hope that everyone will further strengthen self-protection, reduce gatherings, and vaccinate against COVID-19 in a timely manner.

Beijing News reporter Dai Xuan

Edited by Bai Shuang proofread by Chen Diyan