Author: Wu Simin
On the afternoon of November 30, Guangzhou Haizhu issued a circular on optimizing and improving epidemic prevention and control measures, which proposed to do a good job in the isolation management of close contacts.
In principle, close contacts are subject to centralized isolation and observation, and close contacts who meet the conditions for home isolation are subject to home isolation.
Previously, at the work matchmaking meeting held between the Guangdong Working Group for the Prevention and Control of the New Coronary Pneumonia Epidemic and Guangdong Province on the evening of the 27th, the Governor of Guangdong Province, Wang Weizhong, also made it clear that he would support eligible close contacts to implement home isolation to minimize the impact of the epidemic on mass production. life impact.
At present, some special groups of positive infections also have channels to apply for home isolation.
According to the Southern Metropolis Daily short video official Weibo news on the 29th, recently, in the Datang area of Haizhu, Guangzhou, a positive mother had to apply for home isolation because she needed to take care of her depressed son.
In Beijing, China Business News learned from some community residents that for more than a week, some communities have arranged temporary home isolation for asymptomatic and mild COVID-19 infections with the collective consent of building residents.
In addition, in some high-rise buildings and units where positive cases were found, the neighbors who were judged to be in close contact were no longer transferred. Zones are narrowed down to specific floors.
A number of virology and public health experts said in interviews that the implementation of home isolation for close contacts and positive infections who meet certain conditions can alleviate the problem of the rapid development of the epidemic and the shortage of public isolation beds.
At the same time, since the new coronavirus can only be transmitted through aerosols when it reaches a certain concentration and activity, based on this, the probability of non-contact infection in neighbors caused by sewer defecation or opening windows for ventilation in a positive home is very low.
But on the other hand, allowing some people in these two groups to be isolated at home also means that a public health management system needs to be refined to reduce disputes and confusion during implementation and reduce the chance of contact transmission of the virus.
Low probability of infection from sewers and ventilation
A resident of a community with an infected person told Yicai that at present, there are transferees who share the same drainage pipe and have not been transferred. Although most of the neighbors are understanding, will this "positive" neighbor be quarantined at home? She expressed concern about the aerosol transmission of the virus, which would infect non-close contacts with the new crown.
Aerosol refers to tiny solid and liquid particles suspended in gas (such as air), which can diffuse with the flow of air.
Although theoretical studies and simulation experiments have shown that aerosols containing the new coronavirus can be transmitted through the sanitary drainage system of high-rise buildings, many interviewed experts believe that the probability of such non-contact transmission of the virus is very small.
"Sewer infection can only occur in a specific building structure, and it can be avoided by pouring a small amount of disinfectant into the floor drain when necessary." Jin Dongyan, a professor at the Li Ka Shing Faculty of Medicine at the University of Hong Kong, told Yicai.com that the so-called "specific building structure" refers to buildings. The sewer vents of the houses are connected to the manure drains or each family gets air through narrow patios.
In June of this year, China CDC Weekly published a paper on a field simulation experiment related to the new crown.
According to the paper, in March of this year, in a 33-story building in Shenzhen, 62.9% of the confirmed cases lived on different floors in the vertical space of the building. During the on-site investigation, it was found that the drainage pipes of the building had no U-shaped traps, and the floor drains were also damaged. There is no water seal.
Based on on-site controlled experiments, the thesis deduces that, under the background of non-water-sealed floor drains and U-shaped traps, there is a possibility that aerosols containing the new coronavirus may spread through "toilet flushing-soil piles-ground drains".
However, the control experiment used a virus aerosol simulant instead of a live virus or a pseudovirus.
"This study is subject to some limitations. The field simulation experiment is a qualitative study. The experimentally confirmed aerosol transmission of the simulant does not represent the risk of infection caused by the virus," the paper said.
"In fact, even in old communities with direct drainage pipes or high-rise buildings without water-sealed floor drains, the probability of aerosol transmission of the new crown is very low." A virology expert analyzed Yicai.com.
The expert believes that, on the one hand, the new coronavirus survives for a short time outside the host body. In this context, although the phenomenon of "fecal detoxification" exists, the possibility of containing live viruses is small. Even if there is, most of them are not transmissible. , not to mention that the viral load in feces itself is very small; on the other hand, the proportion of viruses in feces forming aerosols is not high, and with the environment, temperature, time, distance and other factors, the viral load in aerosols volume will be further reduced.
Therefore, in the extreme situation where the viral load of a positive infected person reaches its peak, the possibility of virus-containing aerosols infecting neighbors through the sewer pipes "without contact" is also very low.
But he also reminded that for co-residents, the probability of virus transmission in the bathroom space is higher.
Based on this, it is better for positive or close contact persons isolated at home to have an independent toilet. After going to the toilet, cover the toilet lid first and then flush the toilet to avoid the airflow quickly flushing out the virus in the toilet and polluting the environment.
Maintaining air flow can minimize the concentration of virus particles in aerosols, but will opening windows for ventilation cause the virus to spread downwind?
Chang Rongshan, an expert in virology, told China Business News that the peak period of virus shedding from asymptomatic infected persons is generally on the 3rd, 4th, and 5th days, which are also the days when the T line is brightest during antigen detection. The virus in the aerosol spreads outside through the window, and after the outdoor air is sparse, the concentration will drop to a very low level immediately, and the risk of re-infecting others cannot be ruled out, but there are almost no reported cases; There is no risk of transmission.
"It should be noted that as long as the window is opened in the building where the infected person lives, the utensils and clothes of the neighbors around the infected person may have a positive result in the nucleic acid test. This is because it is discharged into the outdoor air The dead virus particles may stick to utensils, clothes, and people's faces, and quantitative PCR will test positive. However, in these cases, the Ct value is generally not very low, such as 32 to 38. Therefore, in the case of neighbors in the same building When conducting nucleic acid testing, PCR positive samples may be found in their samples. At this time, their serum and throat swabs should be tested. If the IGM is negative and the PCR result of the throat swabs is negative, the possibility of close infection can be ruled out.” Often Rongshan said.
Positive home requires a systematic plan
A number of interviewees appealed that although positive infected persons who meet special requirements are allowed to be isolated at home, the possibility of non-contact transmission of the virus is extremely low, but relevant prevention and control plans involving positive cases at home need to be put on the agenda for better maintenance and protection. The rights and safety of infected persons, close contacts and other persons in the same building or unit.
"The new crown epidemic is a major public health event. For asymptomatic or mildly positive patients, if they are isolated at home, an agreement should be reached between the individual and the relevant department. Various guarantees and supervision.” Chang Rongshan said.
A public health expert agrees.
He further told China Business News that "with the consent of the neighbors, positive patients can be quarantined at home and not sent to the shelter" is a voluntary behavior. At present, a set of top-down detailed implementation standards is urgently needed.
"For example, which groups of people can stay at home, which residences cannot be used, how to disinfect during the isolation period, and when to end the isolation. These aspects need to have detailed implementation standards. At the same time, after the positive home, are the control requirements for other residents of the building? There will be changes, and further clarification is needed. Otherwise, even if the neighbors jointly sign the document agreeing to the home isolation of positive infected persons, disputes may still arise in the future.”
From the perspective of the family environment, Jin Dongyan believes that the ideal home for positive patients is to have a separate room and bathroom. If there is no separate bathroom, pouring disinfectant immediately after the infected person uses it can also avoid the spread of the virus.
If it is a positive family with an elderly person, if conditions permit, the elderly can be isolated in a room with a separate bathroom.
But if you are not at ease, infected people can still choose centralized isolation.
The above-mentioned virology experts also believe that for families with elderly people or patients with underlying diseases, when a family member is tested positive for the new crown, it is recommended to transfer and isolate them for insurance purposes, so as to prevent these high-risk groups from being infected. die.
Chang Rongshan believes that in the face of the actual needs of home isolation of positive infected persons who meet special requirements, two aspects of work need to be properly done: one is to guide and cooperate with home isolation personnel to implement strict isolation codes of conduct, including not leaving the room unless necessary, Stay away from cohabitants and pets, do a good job of collecting and processing sputum, nasal mucus and other secretions, and clean and disinfect the environment in a timely manner to reduce the probability of contact transmission of the virus; Timely monitoring.
"When staying at home, it is recommended that positive patients use the antigen quick test card. If necessary, nasopharyngeal swabs that need to be sent outdoors for nucleic acid testing should also be self-sampled to avoid close contact to the greatest extent possible. Cohabitants assist in sampling. It’s best not to happen.” Chang Rongshan said.
According to the ninth edition of the prevention and control plan and the 20 optimization measures, there is a clear time limit for the home isolation period for people in close contacts and high-risk areas. So, if the positive person stays at home, when can the isolation be lifted?
The aforementioned virology experts believe that the ninth edition of the prevention and control plan should refer to the requirements of the "nucleic acid test positive personnel after discharge (cabin)", that is, the nucleic acid test Ct value is ≥ 35.
"There is also a factor that needs to be taken into account. Due to the high probability of breakthrough infection of Omicron BA.5.2, the close contacts who live with the positive person may become positive during the home period of the positive person. Although the isolation of natural immunity Personnel can avoid re-infection. However, how to calculate the time for the household and the building to be released from isolation needs to be refined." The virology expert added.