On December 14, Guangzhou announced the discovery of the first case of Infection with the Aomi Kerong variant in Guangdong Province, the patient was a citizen who received 14 days of isolation and observation after entering the country, and entered the home management stage in a closed loop, disease control experts collected 132 environmental samples in the flow survey, 128 environmental samples tested negative, and 4 positives were found in the residence of the case.
On December 16, a cargo pilot in Guangzhou who had operated an international cargo flight was diagnosed. Disease control experts collected 312 environmental samples in the flow survey, 128 environmental samples tested negative, 1 positive was found in the case residence, and the rest of the results are to be released.
Why do positive samples frequently appear in the residence of confirmed cases? Where did these positive samples come from? How long does THE coronavirus survive after leaving the human body? What should ordinary citizens do? In the face of these confusions lingering in the minds of the public, the Nandu reporter specially synthesized the information of the two press conferences on the 14th and 16th, as well as the professional opinions of Cai Weiping, chief expert of the Eighth Affiliated Hospital of Guangzhou Medical University, and Wang Ming, an expert of special allowances of the State Council and chief expert of the Guangzhou Preventive Medicine Association, to answer them one by one.
Why do I test positive for the disease? Where did it come from?
Since the outbreak of COVID-19, notifications of positive samples tested in the homes where confirmed cases live have been more common. At the beginning of the epidemic in 2020, the disease control personnel in Guangzhou city have tested positive samples on the doorknobs of the families of confirmed cases. Sampling and testing of the environment outside the place where the confirmed case lived and was active is itself part of the epidemiological investigation. For example, the doorknobs, mobile phones, telephones, faucets, keyboards, remote controls, elevator keys, etc. that patients may often touch when they are at home are sampled and detected, which is a means to clearly grasp the characteristics of infectious disease transmission.
Public health residents often focus on disinfecting doorknobs.
The main transmission route of the new crown virus pneumonia is respiratory droplet transmission and contact transmission, and the transmission routes such as aerosol and fecal-oral have yet to be further clarified. "People often don't wear masks when they return home, and it's not uncommon for virus-containing droplets to be brought out through sneezing, coughing, etc., and attached to the surface of commonly used utensils." Cai Weiping analyzed that the positive samples detected in the external environment in such patients' homes are not uncommon after the emergence of previous respiratory infectious disease outbreaks.
Limited by the current environmental sample detection methods, such environmental samples are often detected with virus fragments, which can neither confirm that the virus at the time of testing is dead, nor can it prove that it is alive. "More can only indicate that the virus has come, and the increase in positive samples in the external environment is closely related to the viral load and transmission capacity." Wang Ming said that whether it is Delta, which is still the mainstream strain, or Aomi Kerong, which has been detected in Guangzhou, its characteristics after infection have the characteristics of strong transmission ability.
How long does the virus survive after it leaves the body?
Wang Ming said that how long can the new crown virus survive after leaving the human body? It is greatly related to the temperature, humidity, and whether there is a systematic killing at that time. After the emergence of the new crown epidemic, Japanese public health experts published a study in an academic journal showing that the new crown virus can remain active on human skin for up to 9 hours, which is 5 times longer than the influenza virus. "Compared to the influenza A virus, the new crown virus can survive on human skin for 9 hours, which may increase the risk of contact transmission and thus exacerbate the spread of the epidemic. But (maintaining) hand hygiene reduces this risk. The study also suggests that both the coronavirus and the flu virus can lose their activity within 15 seconds if alcohol-based hand sanitizers are used.
Related studies have suggested that the new crown virus can survive on smooth surfaces such as glass (mobile phone screen) and stainless steel surfaces for a long time.
"In addition to objective influencing factors such as temperature, humidity, and whether there is disinfection, the smoothness of the surface of the object also determines the survival time of the virus after leaving the human body," Cai Weiping said.
Previously, some research reports disclosed that the new crown virus can survive on smooth surfaces such as glass (mobile phone screen) and stainless steel for up to 28 days. The coronavirus is characterized by its survival at lower temperatures and longer on non-porous or smooth surfaces (such as glass, stainless steel, and vinyl) than on porous, complex surfaces such as cotton.
What should ordinary citizens do?
In recent days of briefings, disease control experts and front-line epidemiological investigators have not only surveyed patients, but also conducted external environmental tests in public places, and the external environmental samples obtained were not positive. In fact, this also reveals some important information: the external environment is often ventilated and sunny. "Ventilation can dilute the virus, and ultraviolet rays in sunlight can kill the virus," the two experts told Nandu reporters, it is worth noting that past experience suggests that to reduce the spread of the new crown epidemic, it is also necessary to pay attention to the potential risks in the elevator. "It is recommended that in the future, after the elevator in the residential area is suspended, the gate is open and ventilated, rather than the door is closed," Cai Weiping said.
It is of great significance to pay more attention to window ventilation and prevent respiratory infectious diseases.
"In order to do a good job in the prevention and control of the new crown epidemic, we will recommend that citizens must do a good job of cleaning their homes, wear masks, ventilate frequently, pay attention to personal hygiene, and maintain social distancing." In fact, the discovery of positive samples in the homes of confirmed cases is a reminder that we can reduce transmission through these physical, non-drug means," Wang Ming said, although it is a cliché, but it is actually effective.
Zhujiang New Town, citizens wearing masks after work.
Wash your hands frequently and ventilate more immediately. Also, how long have you not washed your hands and washed your phone with disinfectant wipes?
Written by: Nandu reporter Wang Daobin