As the coronavirus pandemic evolves, more information emerges on how the virus spreads in the community. Recently, the World Health Organization (WHO) recognized that the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes the coronavirus disease (COVID-19), spreads through aerosols, which are small droplets that remain suspended in the air.
Now, a new study reveals that the virus may spread via aerosols through drain pipes in bathrooms, after scientists examined an abandoned apartment in Guangzhou, China. The findings add to the body of evidence suggesting the virus is transmissible via aerosols.
Several studies have revealed that COVID-19 can spread through aerosols in the hospital setting.
Airborne transmission is defined as the spread of an infectious agent through the dissemination of droplet nuclei (aerosols) that remain infectious when suspended in the air for long distances and time, the WHO reports.
Initially, the WHO said that the airborne transmission of SARS-CoV-2 could occur during medical procedures that produce aerosols, such as nebulization. However, recent evidence has shown that airborne transmission can also spread in enclosed areas where there is poor ventilation, such as offices.
Aerosols, which an aerodynamic diameter of <5 μm, can readily penetrate deep into the alveolar regions of the lungs of a bystander. Meanwhile, large droplets are thought to arise from the upper respiratory tract and settle quickly and relatively close to their source.
Spread in bathrooms
A team of researchers from the China Center for Disease Control and Prevention (CCDC), the University of Utah, and the Nanjing Medical University aimed to review the evidence of aerosol transmission of SARS-CoV-2.
To arrive at the study findings, the scientists conducted an “on-site tracer simulation experiment” to evaluate if the virus could spread through waste pipes through tiny airborne particles, which are generated by the force of a toilet flush.
The team noted an incident in February, when SARS-CoV-2 RNA on surface samples, such as those from the shower handle, faucet, and sink, was found in a bathroom of an unoccupied apartment. The bathroom is located on the 16th floor, which was right above the apartment of five people with COVID-19, which were diagnosed between Jan. 16 and Jan. 30.
The team said that an on-site trace simulation experiment also confirmed the possibility of aerosol transport through drainage pipes after flushing the toilet on the 15th floor. The team showed that aerosols were found in the restrooms of apartments on the 25th floor and the 27th floor of the building.
“Although transmission via the shared elevator cannot be excluded, this event is consistent with the findings of the Amoy Gardens SARS outbreak in Hong Kong in 2003,” the authors wrote in the paper, citing unpublished data from the CCDC.
In the Amoy Gardens case in 2003, warm and moist air from the bathroom of a severe acute respiratory syndrome (SARS) patient excreting high concentrations of the virus in feces and urine has established a plume in the air shaft that spread the pathogen to other apartments.
Other sources of airborne transmission
Aside from bathrooms through sewage pipes, the team also cited other instances that airborne spread of the SARS-CoV-2 is more likely. For instance, a choir rehearsal in Washington in the United States has led to the infection of 53 out of the 61 attendees, while two of these patients had died. The rehearsal imposed adequate precautions for droplet transmission, and none of the attendees had symptoms.
Health experts suspect that the virus may have spread through singing, wherein the forceful inhalation and exhalation may have aerosolized the virus, leading to high levels of disease transmission.
“This indoor transmission risk may have been increased because of high occupancy, long duration, loud vocalization, and poor ventilation. A recent study addressed the potential long distances covered by SARS-CoV-2 through cough and sneeze and revealed that small droplets emitted during a sneeze, could reach distances of 7–8 meters,” the authors noted.
Other reports of airborne transmission have been mentioned, such as outbreaks involving cases in relatively confined or crowded environments, including hospitals, public vehicles, offices, shopping malls, and prisons.
“Poor ventilation for a relatively long time and lack of mask use may have increased the risk of aerosolized infection. Taken together, this suggests the possibility of aerosol transmission, especially in confined settings after exposure to high concentrations of viral aerosols for a long time,” the researchers said.
The team urges governments and healthcare settings to impose precautionary control strategies that are essential for the protection of public health. They should inform the general public, particularly the vulnerable groups, about avoiding crowded and poorly ventilated environments.
Since there is a risk of airborne transmission in closed spaces, providing adequate natural ventilation, increasing air exchange rates, and reducing the use of central air conditioning, are all critical. Public transport vehicles should be disinfected regularly, and restrooms should also be thoroughly cleaned regularly.
Most importantly, wearing masks, avoiding crowded places, physical distancing, and proper hand hygiene are still the best ways to prevent infection and spread of COVID-19.
The study is published in the journal Environmental International.