Recently, the confirmed cases of pneumonia caused by novel coronavirus have successively appeared in a department store in Baodi District (the 34th, 36th,37th,43th and 48th cases in Tianjin), causing another clustering epidemic.It appears that no epidemiological correlation can be found among the first three cases based on their symptoms at the onset. Then how did they develop symptoms? Which signs before the onset can be traced back to? How can we find the answer?

At the press conference on the prevention and control of novel coronavirus- caused pneumonia held in Tianjin at 16: 00 on February 2, Zhang Ying, director of the Infectious Disease Prevention and Control Office of the Tianjin Center for Disease Control and Prevention made a detailed analysis of the five confirmed cases related to the department store building in Baodi. The riddle was eventually unraveled.

The 1st case

The 1st case is a sales staff working in the small appliances area of the store.She had a fever on January 22. The store was closed on January 26 for the Spring Festival. After she developed symptoms, the woman saw a doctor in a community clinic for four consecutive days. However, there was no fever department in this clinic. During this period, she suffered from a continuous high fever so that she had to buy some drugs for treatment at home. The symptoms had not relieved by January 30. So she went to the fever clinic of a hospital in Baodi accompanied by her husband on January 31. Then, she was confirmed to have novel coronavirus- caused pneumonia by the Tianjin Center for Disease Control and Prevention.

The key problem is that she had no epidemiological history in Wuhan and had neither been out of Tianjin nor been in contact with similar confirmed cases or cases with suspicious symptoms according to the epidemiological investigation.

The 2nd case

“On February 1, we received the 2nd confirmed case.This patient is the husband of the 1st one. After his wife developed symptoms, he was with her the whole time from the community health service center to the hospital of Baodi. During this period, he developed similar symptoms, ”Zhang said, “The 2nd patient had diarrhea as early as on January 24. In the whole process of seeing doctors with his wife, he just bought some drugs for himself at a small drugstore near his house. Although he had been seeing doctors with his wife, he did not go to any doctor for himself. ”

According to the epidemiological investigation, the 2nd case also had no travel history in Wuhan or other epidemic areas.He had no contact with any other cases of suspicious symptoms but his wife.Therefore, the source of the infection attracted the attention of the experts of the Tianjin Center for Disease Control and Prevention.How did the couple get infected? At that time, the experts inferred that it was probably because his wife who worked in the store brought the coronavirus to her family after contacting customers.However, the 3rd case emerged thereafter.

The 3rd case

The 3rd case is also a sales staff of the department store.She sold jewelry on the same floor as the 1st case, but not in the same sales area.The 1st and 3rd cases had no connection or overlap in daily life, nor did they eat or chat together.The 3rd case did not show any symptoms until January 24. During the epidemiological investigation, experts found that the 3rd patient had a contact with a high fever patient when she restocked goods in a place outside Tianjin on January 18.

“There are cases found in the place where she restocked goods. However, the patient with high fever has neither been clinically diagnosed nor been confirmed by the laboratory.It’s unable to confirm whether the patient who has contacted the 3rd case is a pneumonia patient infected by the novel coronavirus because he did not see a doctor nor was tested.The infection source of the 3rd case remains a question, ”Zhang said.

According to analyses of the experts, there was a possibility that the 3rd patient was infected with the virus and brought it back to Tianjin, which caused the spread in the department store and then in the family of the 1st case.However, the experts could not establish epidemiological links based on the onset time.Why? The 3rd patient developed symptoms on January 24 while the 1st did that on January 22. It did not make any logical sense that the 3rd patient infected the 1st one.

That way, the experts were completely trapped in the riddle. At this point, the 4th case emerged.

The 4th case

The 4th case is also a salesperson of the department store.She worked in the shoe area on the same floor as the 1st and 3rd cases. She said that she had no overlap in work with those two cases.

For fear of missing key clues, the experts visited the department store's leader to ask some questions such as whether the store held get-togethers, small gatherings, summing-up meetings before the Spring Festival, or the staff were convened in other ways. To the disappointment of the experts, the answer was: no. Besides, there is no group dinning environment so that the salesmen all have dinners themselves. Therefore, the three sales staff had no overlap in their daily work.

However, another phenomenon of the 4th case drew the attention of the experts.The patient developed symptoms as early as on January 21.From 12 to 13 January, she went to a shoe wholesale market twice in L City near Tianjin to replenish stocks.

The experts searched the national outbreak report on the Internet and found that there were novel coronavirus cases and local transmission in L City. They thus judged that it was possible that the 4th case was infected during the restocking of goods in L City and developed symptoms after returning to Tianjin. However, how did she transmit the virus to the other two colleagues who had no overlap with her in daily work? There was also no way to establish epidemiological links.

Were the experts trapped in confusion again?

The experts repeatedly asked the 1st, 3rd and 4th patients whether they ever noticed that they had a moment of contact with each other even in the public toilets. But the answer was : no.

This time, the experts came to a deadlock in the epidemiological investigation of the department store.

As they were at their wits' end, a key figure appeared. In the early morning of February 2, the 5th case was confirmed.

The 5th case

The 5th case is not a sales staff in the department store. It is a customer who had been to the department store. From 15:00 to 18:00 on January 23, she shopped in the shoe area where the 4th patient worked and the jewelry area where the 3rd patient worked.She stayed in the department store for more than three hours. She got a fever on January 29 and was confirmed to be a pneumonia case infected by novel coronavirus on February 1.

This customer had no travel history in Wuhan or other epidemic places, nor had she contacted any suspicious cases or diagnosed cases. According to the experts’ judgement, she could only be infected in the department store.

Following the clues, the experts asked the 3rd and 4th confirmed patients whether they were at their posts from 15:00 to 18:00 on January 23. The answer was: Yes.

At this point, the experts finally established epidemiological links.The conclusion was that the 4th case was infected outside Tianjin, and developed symptoms after returning to Tianjin, which caused the spread of the virus in the department store.Then the customer got infected there.And afterwards the 1st case infected her husband.

“Although the 1st, 3rd and 4th patients work in different areas, they are in the same floor and are adjacent with no clear boundary separating each other. The distance between them is not kept at over four or five meters. It is even actually less than one meter. In such an environment, a customer was infected within three hours. We can imagine that a salesperson who works for eight hours a day cannot avoid being infected,” Zhang further analyzed.

At this point, the cause and effect of the cluster of pneumonia cases in the department store in Baodi are completely clear.

The infection of the Ye’s family in Dongli district deserves a warning.

Zhang Ying also analyzed the infection process of the 39th, 40th and 41st confirmed cases in Tianjin, who are three members of the Ye’s family.The process is relatively simple, but it also serves as a warning. The family are from Wenzhou, living and working in Tianjin. They returned to their hometown to visit their relatives in Wenzhou on January 20. From 20 to 25 January, they attended three gatherings: the first was on January 21 with Tang participating; The second was on January 23 with Ye’s mother and Tang participating.The third was in his mother-in-law's house on January 24. On January 30, Tang was diagnosed as pneumonia infected by novel coronavirus in Wenzhou. On the following day, Ye's mother was tested positive and was also diagnosed. By February 1, all three members of the Ye’s family had been diagnosed. It is all attributed to gatherings. ”

Through the analysis of the these cases, Zhang Ying earnestly reminded the citizens that the prevention and control of novel coronavirus cannot be taken lightly.

“We keep telling everyone how to do it and how to prevent it. What I want to remind you is that you should guard yourself better than guarding against others. One feature of the respiratory infectious diseases is that you do not know who carries the virus.You do not know who gets infected around you.So it is impossible to know who is the case of novel coronavirus,” said Zhang.

What should we do to protect ourselves?

Don't get together with relatives and friends. “First of all, don't get together with relatives and friends. Everyone should have a good rest at home during the holiday after a busy year. If you take good care of yourself, the cases will be fewer and fewer, and the possibility of transmission will be cut off. That way, the epidemic will be under control as soon as possible, and everyone can return to work and study smoothly and earlier.If you run around, there is no way for us to prevent and control it,” Zhang said.

Don't go to public places. “Look at the example of the department store, the infected customer stayed there for merely three hours. Such a relatively closed and densely populated area is a place where respiratory infectious diseases are particularly easy to spread. It is hard to prevent. In addition, our own protection is not up to standard, so don’t go to such public places unless it is necessary.”

Don't take medicine indiscriminately. “Among the five cases found in the department store in Baodi, none of the first four cases went to the fever clinic immediately. They all bought and took medicine themselves in the pharmacies. They didn't go to the hospital until the disease was out of control.Once again I want to remind everyone not to take medicine indiscriminately at home, which will bring many side effects,” Zhang said.

Go to the fever clinic the first time. “The common fault of the first four cases in the department store in Baodi is that after having a fever, their first choices are going to a community clinic instead of the fever clinic, which is very dangerous.Once again, I solemnly remind you that if you or your family have a fever, you should go to the 47 fever clinics publicized by the Tianjin Municipal Health Commission immediately. You can go to the nearest one in your district.”