Right now, as the resumption of work and production continues, the prevention and control of public transport epidemics has become more important.
Surging News (www.thepaper.cn) noticed that recently, a study has been conducted to investigate the possibility of aerosol transmission in a confined environment, taking the case of an aggregate epidemic of 13 people infected by public transportation.
The study found that the new type of coronavirus has a strong ability to spread, the maximum distance of transmission in the air-conditioned compartment is 4.5m, and the virus can float in the air for at least 30 minutes and cause infection. Therefore, it is recommended to take personal protection when boarding public transportation, and at the same time ensure ventilation and fresh air volume in public transportation, and clean and disinfect the compartment.
1 person took the bus, infected 8 people in the same car
The study was entitled "An Epidemiological Survey on the Aggregative Epidemic of New Coronavirus Pneumonia Transmitted by Aerosols in Public Transport." The "Practical Preventive Medicine" sponsored by the Chinese Preventive Medical Association was first issued on March 5. The authors include Luo Weiwei, Haizheng and others.
The study introduced a clustered outbreak that occurred in a certain place in Hunan Province and was caused by public transportation: On January 28, B reported a suspected case of new coronary pneumonia (case A).
The patient developed symptoms on January 22 and was diagnosed on January 29. He and his colleague Li Moumou (confirmed case, onset of January 16) had experiences of sharing meals and working on the 5th and 3rd days before the onset of the disease.
At 12 o'clock on January 22, Case A (without a mask) took the Jiadi bus and arrived at B at 14 o'clock, resulting in the onset of 7 people in the same car (Case B-Case H), in addition to an asymptomatic infection (Case I ).
At 15:40 on January 22, Case A (without a mask) took the shuttle bus and the journey took about 1 hour, resulting in the onset of 2 people in the same car (Case K and Case L).
On the same day, the case A's bus arrived at Site B, stayed for 30 minutes (the vehicle was not disinfected during the stay), and returned to Site A. One passenger (case J) took the car (the seat is close to the seat that was taken before case A) and became sick on January 24. According to the investigation, case J had no other history of special residence and contact.
The epidemic also triggered three successive cases: Case B and Case K were followed by one relative, Case M and Case N.
Under what circumstances did this cluster outbreak that caused 13 people's infections occur?
Studies show that Case A took a 49-seater fully air-conditioned passenger bus at noon on January 22. The first floor of the bus is a luggage compartment, and the second floor is a passenger compartment. The bus is 11.3m long and 2.5m wide. The driver's seat is in the frontmost high-rise, with a total of 48 passengers besides the driver. When the vehicle leaves the station, it takes 46 people and picks up 2 people on the roadside.
The distance between Case A and the nearest infected person (case E) on the vehicle was less than 0.5m, and the distance between the farthest infected person (case G) was about 4.5m.
According to investigations, Case G and Case A got on and off the front and rear doors of the bus, respectively, and there was no close contact on the way. Taking a video from the car at that time, it was found that most people on the car were not wearing masks, and no cases were infected on the car.
In the afternoon of January 22, Case A took an 18-seater air-conditioned minibus with the windows not open. The car is 5.5m long and 2.5m wide. In addition to the driver, there are 17 seats. There were 12 people in the car, only one of them was wearing a mask, and the two infected people on the car were not wearing a mask. The distance between case A and the farthest infected person (case K) was about 4.5 m.
New crown virus has aerosol transmission potential in confined environments
The study pointed out that a total of 243 close contacts were found in the clustered outbreak, including 10 confirmed cases and 1 asymptomatic infection. The close contacts M of the second-generation case B and the close contacts N of the second-generation case K also became ill.
In addition, except for 10 cases of second-generation cases and 1 case of asymptomatic infection who were exposed to the bus together with confirmed case A, the investigation found no other clear epidemiological (exposure) history. Except for two third-generation cases, each had a clear history of contact with one confirmed case in this case, and the investigation found no other epidemiological (exposure) history.
The study suggests that the clustered epidemic has two important implications for the transmission of the new coronavirus.
First, in a closed air-conditioned compartment, the virus transmission distance may exceed the currently considered droplet transmission distance (usually 1m). In this survey, Case A was riding a fully enclosed air-conditioned bus, and the distance to the furthest infected person (Case G) was about 4.5m.
"The possible reason is that in a fully enclosed space, the flow of air is mainly driven by the hot wind generated by the air conditioner. The rise of hot air can transport virus-borne droplet particles to a greater distance, far beyond the commonly recognized 1m distance. The study said that the long-distance transmission in this outbreak also suggested that the new coronavirus may have the possibility of aerosol transmission in a confined environment. Moreover, in a closed environment affected by air-conditioning wind, the transmission distance of the new coronavirus will exceed the commonly recognized distance of 1-2m.
The second is that the effective survival time of the virus in the compartment is not less than 30 minutes, and the virus stock can reach a level sufficient to cause human disease. For example, after the case A passenger took a 30-minute bus stop in Site B, a passenger (Case J) took the bus to return to Site A. In the process, the infection developed.
Studies have shown that the clustered epidemic has some hints on the personal protection of the public, especially passengers traveling on public transport.
During the epidemic, travel personnel should prepare protective articles and prepare a certain number of medical masks, hand-free disinfectants, etc. according to the length of stay and the state of sanitary facilities at the place of travel. When riding in more closed public transportation such as subways, cars, and airplanes, you should wear a mask during the whole process, while minimizing the contact between your hands and public areas, and avoid touching your face before cleaning. Air circulation should be maintained as much as possible, and windows of the car, including the driver's cabin, should be opened in moderation. In the case of closed / air-conditioned carriages, the fresh air supply volume should be adjusted to the maximum to increase the number of ventilations. Under normal circumstances, the inside of the car is cleaned and disinfected 1-2 times a day. Pay special attention to clean and disinfect the interior space of the car once after arriving at the terminal.
The surging news noted that the "New Coronavirus Pneumonia Prevention and Control Plan (Fifth Edition)" issued by the General Office of the National Health and Health Commission on February 21 pointed out that the main route of transmission of new coronaviruses is through respiratory droplets and contact transmission. There is a possibility of aerosol transmission in a closed environment when exposed to high concentrations of aerosols for a long time, and other transmission routes remain to be determined.
On March 3, the "New Coronavirus Pneumonia Diagnosis and Treatment Program (Trial Version 7)" issued by the General Office of the National Health Commission and the Office of the State Administration of Traditional Chinese Medicine also clearly mentioned that the new coronavirus "grows in a relatively closed environment. There is a possibility of aerosol transmission when exposed to high concentrations of aerosol over time. " At the same time, as new coronaviruses can be isolated in feces and urine, attention should be paid to aerosols or exposure to environmental pollution caused by feces and urine.
Regarding the survival time of the virus, Jiang Rongmeng, a member of the expert group of the National Health and Medical Commission and the chief physician of the Second Department of Infectious Diseases of Beijing Ditan Hospital, once introduced that the study found that the virus can survive for several hours on smooth surfaces. If the temperature and humidity are appropriate, they may survive for several days, and may even reach 5 days.
Surging journalist He Niantai