The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has threatened public health around the world.
It has caused over 318 million confirmed cases and 5.5 million deaths as of January 17, 2022. SARS-CoV-2 can be transmitted through air or droplets. Additionally, current quarantine policies do not prevent aerosol transmission and epidemiological surveys alone are unable to prove the transmission path.
Airborne transmission of SARS-CoV first occurred through floor drains in an apartment complex in Hong Kong in 2003. SARS-CoV-2 has been reported to cause a cluster infection similar to SARS-CoV. In other cities, COVID-19 cases have been linked to plumbing faults and aerosol transmission from excreta.
A new study published in The Journal of Infectious Diseases Investigated COVID-19 cases in an apartment complex in South Korea between 10 and 27 January 2021. The study also explored the possibility of aerosol transmission without direct contact between infected individuals with the help of molecular phylogenetic analysis and epidemiological surveillance.
The study involved collection of clinical and epidemiological information from 5 patients who lived in apartment complexes and tested positive between 10 and 27 January 2021. Global Positioning System (GPS) tracking for the investigation of exposure history, contact history, and likelihood of outbreaks was carried out. Additionally, all residents living in vertical lines 1 and 2 in the apartment also underwent SARS-CoV-2 reverse transcription-polymerase chain reaction (RT-PCR).
Environmental samples were subjected to SARS-CoV-2 RT-PCR test after collection on 28 January and 1 February. Architectural schematics and on-site measurements were made for field and environmental investigations. The air flow around the drains and vents in the bathroom was examined with an anemometer and visualized using a smoke generator.
In addition, next-generation sequencing was performed to obtain the complete genome sequence of SARS-CoV-2. Finally, phylogenetic analysis was performed to analyze the relationship between patient and environmental samples.
The results revealed that out of 19 confirmed COVID-19 cases, 14 were caused by close or direct contact-based transmission involving two of the patients. In the case of environmental samples, of the first four positive samples for set one, three were from the door latch and one from the washbasin, while for the four positive samples of set two, one was from the washbasin, and three were from the floor drain.
The results also revealed that both clinical and environmental samples of SARS-CoV-2 belonged to the B.1.497 lineage, the GH clade. In addition, three clinical samples from the apartment floor and one environmental sample were found to contain the same amino acid substitution (A6914V) in the ORF1ab region.
Therefore, the study provided strong molecular evidence that airborne transmission of SARS-CoV-2 may occur through floor drains due to non-functioning drain traps. The study also highlights the importance of environmental sampling in determining epidemiological links between patients. However, more research needs to be done to identify and control the routes of transmission of SARS-CoV-2 and other respiratory viruses. In addition, floor drains and traps should be installed in structures and ventilation systems of vulnerable facilities should be constantly monitored.
The study had some limitations. First, no viable virus was detected from environmental samples.
Second, data on exposure and exposure history to COVID-19 may not be highly accurate due to recall bias.
Third, the effects of corridors and stairs in the transmission were not investigated.