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According to the US Centers for Disease Control and Prevention (CDC). In the USA, the human SARS-CoV-2 virus is believed to spread primarily between people through inhalation of respiratory droplets loaded with the virus, as well as by touching and then touching contaminated surfaces. susceptible areas of the body, such as the mouth, nose, or eyes.
SARS-CoV-2 may also be spread by aerosol particles. Several other respiratory diseases are transmitted by air, such as tuberculosis, measles, and smallpox. In addition, a retrospective study of the 2003 severe acute respiratory syndrome (SARS) epidemic showed that airborne spread of the disease played an important role in transmission. However, very little is known about the aerodynamic properties and transmission pathways of SARS-CoV-2 in aerosols, probably due to the difficulty of sampling and low concentration quantification.
In the current study, a group of Chinese researchers led by Yuan Liu, PhD, of Wuhan University, took a sample of SARS-CoV-2 aerosol deposition at 30 locations within two Wuhan hospitals and subsequently quantified the Aerosol copy counts of SARS-CoV-2 samples using a detection method based on a robust digital polymerase chain reaction (PCR) (ddPCR). The two hospitals were used exclusively for the treatment of patients with COVID-19 during the outbreak: one was a university hospital designated for the treatment of severe cases, while the other was a field hospital used to treat patients with mild cases.
Samples were collected from patient areas, medical personnel areas, and public areas within hospitals. The researchers collected three types of samples:
- Total suspended particle aerosol samples with no upper size limit to quantify SARS-CoV-2 RNA concentrations in aerosol
- Aerodynamic aerosol samples segregated by size to determine the size distribution of SARS-CoV-2 in the air
- Aerosol deposition samples to determine the airborne SARS-CoV-2 deposition rate
Overall, the researchers found very low or undetectable concentrations of SARS-CoV-2 in the air in university hospital patient areas, which they attributed to effective isolation and high air exchange. The highest concentration of SARS-CoV-2 in field hospital patient areas was found in mobile patient bathrooms (spaces of approximately 1 m2 without ventilation).
Again, the medical staff areas at the university hospital had lower concentrations of the virus compared to the field hospital. Particularly high concentrations of SARS-CoV-2 were observed in protective clothing removal rooms. Liu and her colleagues suggest that virus-laden aerosols can be resuspended in the air when personnel remove their protective gear.
SARS-CoV-2 concentrations in public areas were also typically very low or undetectable. However, two high-traffic areas, including an outer space near one of the hospitals, had elevated concentrations of SARS-CoV-2 RNA.
Relatively high amounts of aerosol deposition in patient rooms could also lead to surface contamination and contact of susceptible individuals. Even higher levels were observed in the field hospital where the patient areas were not ventilated or isolated from the hallways. After reducing the patient’s concentration and implementing rigorous and comprehensive disinfection measures, the concentration of SARS-CoV-2 was reduced to undetectable levels. The authors noted that this emphasizes the importance of disinfection in high-risk areas to control the spread of the disease.
Despite the small sample size of this study, Liu and colleagues advocate ventilation and sterilization of toilets in patient areas and other high-risk areas within hospitals as possible sources of spread of SARS-CoV-2, avoiding crowds to reduce the risk of exposure to the virus, and implementing early identification and diagnosis of infected carriers for quarantine or treatment.
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