Study reveals aerosol transmission of SARS-CoV-2 via floor drains

The coronavirus disease 2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has threatened public health throughout the world.

It has led to over 318 million confirmed cases and 5.5 million deaths as reported January 17, 2022. The transmission of SARS-CoV-2 can be airborne or through droplets. Additionally, the current quarantine policies do not prevent aerosol transmission and epidemiological surveys are unable to prove the transmission path alone.

Airborne transmission of SARS-CoV was first reported in 2003 via floor drains in an apartment complex in Hong Kong. SARS-CoV-2 has been reported to have cluster infections similar to SARS-CoV. In other cities, COVID-19 cases have been associated with plumbing defects and aerosol transmission from excrement.

A new study published in The Journal of Infectious Diseases investigated COVID-19 cases in an apartment complex in South Korea between 10th and 27th 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.

About the study

The study involved the collection of clinical and epidemiological information from 5 patients who resided in the apartment complex and had tested positive between 10th and 27th January 2021. Global positioning system (GPS) tracking for investigation of contact history exposure history, and the possibility of spread 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 testing after collection on 28th January and 1st February. Architectural schematics and on-site measurements were carried out for field and environmental investigations.  The airflow around drains and vents in the bathroom was investigated with the help of an anemometer and visualized using a smoke generator.

Furthermore, next-generation sequencing was done to obtain the complete genome sequence of SARS-CoV-2. Finally, phylogenetic analysis was carried out to analyze the relationship between patient and environmental samples.

Findings

The results reported that out of the 19 confirmed COVID-19 cases, 14 occurred due to close or direct contact-based transmissions linked to patient two. In the case of environmental samples, the first four positive samples for set one included three from the doorknob 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 reported that both the clinical and environmental specimens of SARS-CoV-2 belonged to the B.1.497 lineage, GH clade. Moreover, three clinical specimens and one environmental sample from the floor of the apartment were found to comprise of the same amino acid substitution (A6914V) in the ORF1ab region.

The study, therefore, provided strong molecular evidence that airborne transmission of SARS-CoV-2 can occur through floor drains due to non-functioning drain traps. The study also highlights the importance of environmental sampling in determining epidemiological links among patients. However, further research needs to be done to identify and control the routes of transmission of SARS-CoV-2 and other respiratory viruses. Moreover, traps should be installed in the floor drains and structures and ventilation systems of vulnerable facilities must be continuously monitored.

Limitations

The study had certain limitations. First, viable viruses from environmental samples were not detected.

Second, the data on contact and exposure history to COVID-19 may not be highly accurate due to recall bias.

Third, investigation on the effects of corridors and stairs in transmission was not carried out.

Written by

Suchandrima Bhowmik

Suchandrima has a Bachelor of Science (B.Sc.) degree in Microbiology and a Master of Science (M.Sc.) degree in Microbiology from the University of Calcutta, India. The study of health and diseases was always very important to her. In addition to Microbiology, she also gained extensive knowledge in Biochemistry, Immunology, Medical Microbiology, Metabolism, and Biotechnology as part of her master's degree.