Commuting, studying for exams, traveling, caring for children …… As the first infected person found in this round of the outbreak in Shunyi, Beijing, Fu just’s life had been “outlined” in this way by the Beijing outbreak flow survey.
However, his infection began with a shopping experience at a shirt store, but it was only after Beijing’s CDC staff went through multiple rounds of flux that the answer was revealed.
In the six days since Fu was just diagnosed, Beijing has added 17 new native infections of New Crown Pneumonia, with three places upgraded to medium-risk areas. On December 30 last year, the Beijing CDC made public for the first time the traceability results of the localized clustering outbreak in Shunyi – Fu Gang was infected by shirt store employee Chen Pingyan; Chen Pingyan was infected by Indonesian customer Yu Miao. Genetic sequencing confirmed that the source of the outbreak was imported from abroad and that Yu Miao was the source of the outbreak.
If the cases of the 16 infected people are like a tangled ball of thread, a clear chain of transmission is a “brain-burning” story of deduction.
On December 30, 2020, the Beijing Center for Disease Control and Prevention (BCDC), the flow has been visualized. The spots in the picture represent the areas where there is an outbreak. Photo/Xinjing News reporter Wang Jianing
Who actually infected whom?
In an outbreak involving many cases, there are always a few core cases that act as transportation hubs, linking upstream and downstream and converging to the original source. The earliest cases, Fu Gang (the first infected person found on Dec. 23 last year), Xie Yang (diagnosed on Dec. 25 and working in Chaoyang District) and Zhang Shenqiu, were seen as the core of the traceability.
Ye Yan is the deputy director of the Beijing CDC and the head of the city’s CDC sent to Shunyi District for on-site support. In his impression, Zhang Shenqiu is particularly prominent among the three.
Zhang Shenqiu’s appearance was somewhat fortuitous. She is a native of Hebei, 31 years old, working in a convenience store Shunyi District freight store. On the afternoon of Dec. 24 last year, she went to Dongcheng District for a nucleic acid test – not because of a history of close contact, but because the store sells cold food and the company arranged for employees to be tested for nucleic acid in accordance with Beijing’s epidemic prevention requirements.
On December 25, Zhang Shenqiu was diagnosed, and the following day, six of her close contacts were confirmed to be infected, five of whom were socially connected to Zhang Shenqiu, and one of whom had picked up Zhang Shenqiu as an online taxi driver.
The more “pieces” that can be linked together, the easier it is to form an outline. At that time, pay just and solve Yang are isolated cases, only Zhang Shenqiu and new cases clearly form a relationship, or can provide more clues. This “clump” of seven people became the focus of attention of Ye and colleagues.
The core question to be clarified is, among the 7 people, who actually infected whom?
Perhaps nothing is more obsessed with the order of priority than the flow of investigation. Ye Yan introduced that tracing the source is a reverse reasoning, from the latest case, all the way backward to the initial case, the order is right, in order to determine the source of infection. Zhang Shenqiu is the first of the seven cases to enter the public eye, it seems reasonable to put her in the “uppermost”, but is that really the case?
“To find the sequence, an important reference standard is the onset of time, but this is also not easy to figure out, need to double-check.” Ye Yan said.
CDC staff conducted multiple rounds of flow of seven people. Chen Yanwei, a physician in charge of the Beijing CDC, participated in the supplementary investigation, and she recalled that in the first round of flow investigation, Zhang Shenqiu said that on December 20 last year, he had taken a net car with the case Chen Pingyan (Zhang Shenqiu’s hometown, Shunyi Hualian second floor shirt store employee) and went shopping at the Houshayu Town’s Wumai supermarket, but Chen Pingyan did not remember. In the official first published flow investigation report, Chen Pingyan mentioned December 20 had gone to the Aishang fresh supermarket shopping, did not mention the physical supermarket.
In order to clarify the close connection between the two, Chen Yanwei pursued Chen Ping-Yan, after carefully recalling and looking up the payment records, Chen Ping-Yan remembered the matter.
The onset time is also further amended, at first, Zhang Shenqiu onset earliest, Chen PingYan said she was not uncomfortable, flow transfer personnel reminded her that other symptoms such as headache, fatigue also count, Chen PingYan only to give a positive answer, the time of symptoms, also become earlier than Zhang Shenqiu, become the earliest of the seven people.
After the upstream position of Chen Ping-Yan was clear, the transmission relationship of 7 people was smoothed out. Chen Pingyan infected her husband Chen Zhi, the driver of the online taxi, fellow countrymen Zhang Shenqiu and Chen Yue who were riding in the same online taxi; Zhang Shenqiu and Chen Yue, in turn, infected their respective husbands Chen He and Chen Ming.
What excites Ye Yan is that Chen Ping Yan’s presence has linked Fu Gang, who originally could not find the source of the infection.
The Beijing Center for Disease Control and Prevention, Chen Yanwei produces the flow investigation report will telephone interview the epidemic-related personnel. Photo/Xinjing News reporter Wang Jianing
Three strains combined into two
From December 23 to 25 last year, a localized outbreak in Shunyi found three infected people, Fu Gang, Zhang Shenqiu and Xie Yang. Is there a transmission relationship between these three, which directly affects the delineation of the source of infection – is it the same source, or multiple sources?
Wang Xiaoli, deputy chief physician at the Beijing CDC, is responsible for tracing the source of the outbreak. She recalled that in the first few days, CDC staff had been trying to find out the close contact history of the three men, with very little success. Among them, Zhang Shenqiu and Xie Yang’s trajectories did not overlap at all; the possibility of contact between Fu Gang and the two men could never be conclusively established.
First of all, Fu just and Zhang Shenqiu. According to the investigation, the two have gone to the Houshayu town supermarket, but before and after the day to go, there is no complete intersection in time and space. Considering the possibility that people contaminated items environment, and then infected to people, the CDC personnel went to the supermarket for the site sampling, the results were negative, repeat sampling, still no contamination was found, the relationship between the two was not established.
So, pay just and solve Yang have a relationship? The two live not far apart, pay just been to Shunyi Hualian Commercial Building, Hualian Commercial Building is very close to Xie Yang’s home, less than a kilometer, but did not find clues that the two went at the same time; pay just took the bus past the Shunyi District Hospital, close to Xie Yang’s home, but still no direct evidence of the relationship between the two, and can not be established.
Chen Pingyan’s appearance changed the situation.
Chen Pingyan is Shunyi Hualian commercial building second floor shirt store employees, December 17 last year had gone to work in the commercial building. According to Fu just self-reported, on December 17, he had gone to the first floor and third floor of Shunyi Hualian Commercial Building (Shunyi Store), and did not go to the second floor.
The distance is so close, really no contact?
Ye Yan introduced, the disease control officers then went to the commercial building again to investigate, to find the day of the surveillance video, found that pay just went to the second floor, and in Chen Ping Yan work store stayed for more than twenty minutes, compared to the previous seemingly clues, this evidence is very strong.
Pay just therefore associated with Chen Ping Yan and other 7 people. The three “teams” were merged into two, leaving only Xie Yang as an isolated case.
The detailed flow investigation report produced by Chen Yanwei. Photo/Xinjing News reporter Wang Jianing
The last piece of the puzzle
Xie Yang “joined the team” after asymptomatic infected person Yu Miao was discovered.
Where exactly did the virus come from? Ye Yan introduced a variety of scenarios within the CDC – it could have been brought in by imported cases from outside the country, it could have been attached to cold-chain imported goods, or it could even have occurred directly locally, but none of them could be verified until Yu Miao was confirmed.
While the flow was being transferred, another means of traceability – whole genome sequencing – was also underway.
The principle of PCR nucleic acid testing is to determine whether the sampled person is infected by comparing whether several key gene fragments of the new coronavirus can be amplified in the sample; whole-genome sequencing, on the other hand, can thoroughly analyze the genetic sequence of the new coronavirus. There are multiple prevalent strains of the new coronavirus, which are prevalent in different regions of the world. Comparing a gene sequence to a global gene pool can suggest the geographic origin of the virus by finding the most similar sample of the strain.
After Fu just tested positive, the CDC quickly collected a sample of his new coronavirus for sequencing. On December 25 of last year, Wang Xiaoli got the results and found that it belonged to the L genotype European family branch 2.3, a strain recently prevalent in Southeast Asia, not a strain from Beijing or a previous domestic virus.
This was a clear indication that the virus was imported from outside of China. After that, the CDC staff started looking for clues from outside of China among the existing cases and found that Yu Miao, the roommate who lived with Xie Yang, was from Indonesia. Immediately, an emergency nucleic acid and antibody test was performed on Yu Miao, and the results that night were very exciting for Wang Xiaoli – although negative for nucleic acid, positive for IgM antibodies, suggesting that he was or had been infected. Environmental sampling of his living space and work space also detected positive nucleic acid for the new coronavirus, confirming his detoxification.
Xie Yang and Yu Miao’s residence, close to the Shunyi Hualian, Yu Miao and Chen Ping Yan whether there is a contagious relationship? Ye Yan introduced further investigation found that Yu Miao had gone to Hualian on December 13 last year, and close contact with Chen Ping Yan.
This became the last piece of the puzzle, the seemingly unrelated Xie Yang, Chen Ping Yan 7 people in the chain of transmission “convergence”.
Wang Xiaoli (center) and colleagues check the flow of information at the Beijing Center for Disease Control and Prevention. Photo/Xinjing News reporter Wang Jianing
The chain of transmission has been uncovered
Yu Miao may be patient No. 1. But was he infected before other cases, and by whom?
The deputy director of the Beijing CDC, Pang Xinghuo, said that although Yu Miao lives in Shunyi, he is actually a young man of Indonesian origin who has been living in Indonesia for a long time. The company’s main business is to provide a wide range of products and services to the public.
Wang Xiaoli recalled that after locking in Yu Miao, they investigated the information on the outbreak in Fujian on that day and found that there was indeed an imported case from abroad; they investigated the flights arriving in Fujian from Indonesia on the day of Yu Miao’s entry and found that there was only one flight between Yu Miao and the local Fujian CDC to get the report of the imported case. It is likely that Yu Miao was infected by the case.
On December 30 last year, the Fujian CDC provided feedback on the gene sequence of the imported Indonesian case in the same row as Yu Miao, and the Beijing CDC found that the nucleotide similarity was 99.99%, which is highly homologous. The comprehensive sequencing results showed that the 14 infected cases and 5 copies of the associated environmental viruses were highly homologous, the same transmission chain, and the source of infection was imported from abroad.
In addition, after Yu Miao was admitted to the hospital, the staff detected positive nucleic acid in her stool sample. Wang Xiaoli explained that, in general, positive respiratory specimens, earlier than positive digestive specimens, this clue suggests that he has been infected for some time.
Pang Xinghuo said that the comprehensive investigation evidence, the local aggregated outbreak in Shunyi District is a single chain of transmission. Yu Miao was the source of the aggregated outbreak, and upon arrival in Beijing spread the virus to his roommate Xie Yang, who in turn spread it to Chen Pingyan during his shopping trip.
Chen Pingyan transmitted the virus to the first infected person, Fu Gang and her husband, Chen Zhi, during work; to fellow villagers, Zhang Shenqiu and Chen Yue, during common gatherings, shopping and car rides; and to the driver, Wang Yan, during a ride in an online taxi.
Wang Yan spread to Ma Wei, the driver of the online taxi (diagnosed on December 28 last year), during the joint dinner; Zhang Shenqiu and Chen Yue infected their husbands respectively; in addition, the three husbands and Chen Yue worked in the Golden Horse Industrial Park, which led to the infection of five colleagues through joint work and gathering activities such as dinner.
At this point, the entire transmission chain has been uncovered.
The transmission chain of this Shunyi outbreak. Cartography / Shi Chunlei
Behind the “solved” case
The scale of this localized outbreak in Shunyi does not seem to be large, with only 16 infected people found in six days, compared to 36 new cases in one day during the last round of the outbreak in Xinfaodi.
But behind the small number of cases lies a lot of front-line work.
Ye Yan introduced, each case is accompanied by repeated flow investigation, field sampling and huge close receiver management. The flow investigation report is the basis for analysis and sampling, which can rarely be done at once, especially at the very beginning, when there are few cases and few clues, and they do not know what information is crucial, so they need to be asked in great detail; later, new clues and new hypotheses emerge, which need to be supplemented and verified by the previous cases, and they have to be pursued again; when the patients themselves are in bad condition, the time of flow investigation is shortened and the number is bound to increase. In this epidemic, some individual cases were investigated more than ten times.
Field sampling is based on flow reports. After the initial flow investigation report appears, the sampler has to go to key points to retrieve video, delineate the close connection, and sample the environment. As reports are updated, new cases are added, and relationships between cases emerge, a site may have to be visited multiple times over.
Close receiver management is equally difficult, a case of close contact with the basic nearly 100 people. Shunyi District Standing Committee, Executive Vice Mayor Zhi Xianwei introduced, as of December 30, last year at 12:00, Shunyi has tracked and identified 1239 people close contacts, have been implemented to control. The number of close contacts is even larger.
In order to complete the investigation of the dozen cases, the management of the close contacts, the Beijing CDC sent to the scene more than 20 people, the back trace, testing, information collation and other work invested in hundreds of people; Shunyi District CDC full participation, Fengtai, Daxing, Fangshan, Mentougou and other districts CDC also sent support staff; some districts, although there is no confirmed cases, received a cross turn of the close contacts, but also to start the management. “The CDC system put in how many people, specific statistics are not available, but the total number should be more than a thousand.” Ye Yan said.
In addition to the CDC system, the public security department, the Shunyi District township government, the streets, the units involved, all took on important work to contribute to the flow of traceability and prevention and control of the epidemic.
In addition to the imperceptible pay, behind the case, there is also a hidden life of all kinds.
Some netizens nicknamed him “Inspirational Brother” because his life was filled with commuting, studying, traveling and caring for his children.
There are also those who are concerned.
“It’s hard for patients with infectious diseases to avoid discrimination.” Dou Xiangfeng, director of the Institute of Infectious Disease and Endemic Disease Control at the Beijing CDC, said that since last year, the privacy of many newly crowned patients and close contacts has been leaked, and some have been subjected to cyber violence as a result; after the diagnosis is confirmed, will the infected be socially ostracized, dealt with by their units, and face an even worse situation?
“They are also victims, many life is not easy, even the children can not bring around to raise. I hope they will be treated with more understanding and kindness.” Dou Xiangfeng said.
Pang Xinghuo, who attended a conference on the prevention and control of the epidemic in Beijing on Dec. 29, 2020. Photo/Xinjing News reporter Wu Ning
Conversation
Pang Xinghuo, deputy director of the Beijing Center for Disease Control and Prevention: the biggest wish is to return to normalcy
Xinjing News: The scale of this epidemic is relatively small, has it been easier to trace the source of the flow compared to the time of the new development?
Pang Xinghua: Although there are few cases this time, it is still not easy to trace the source. Beijing has not had any local cases of unknown origin for a long time, people are more relaxed, the flow of people is large, and there are many gatherings, the trajectory is very complicated; a case suddenly emerged, the first few are not yet associated, these have increased the difficulty. Later on, the number of cases increased, the evidence increased, and the flow of investigation only gradually became clearer.
Xinjing News: We found a change, from December 23 to 25 of last year, a few cases are accidental detection or active medical discovery, after the 26th is basically close to confirm the diagnosis, what does this mean?
Pang Xinghuo: We control the right, control of the people in the case is normal, if the control outside the scope of the case, it means that the case and dense connection has not been found in full. The latter did not make a strong effort to bubble up, there should not be a stronger gathering of epidemic occurred.
Xinjing News: After counting the existing cases, there are no serious cases yet, and the condition of the patients seems to be much lighter than the previous rounds of the epidemic, why?
Pang Xinghuo: On the one hand, the early detection, many in the early state, asymptomatic, mild symptoms, timely admission, can reduce their symptoms; on the other hand, the accumulation of treatment experience, this year, our medical institutions are also experienced in a hundred battles, the new crown although there is no special drugs, but there are many other effective treatment means.
Xinjing News: What is your biggest wish now?
Pang Xinghuo: The biggest wish is to return to normalcy. It has been a bad year for everyone. Life has been completely disrupted by the epidemic, and we can’t move freely, friends and family can’t gather at will, and we can’t go out to play. This special period, or the need for departments and units to do a good job of personnel management, epidemic prevention and control, I hope that the public can hold on to the protective measures in place to minimize the risk of the spread of the epidemic.
(All infected persons in this article are pseudonyms)
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