Thursday, November 03, 2022

EID Journal: Probable Aerosol Transmission of SARS-CoV-2 through Floors and Walls of Quarantine Hotel, Taiwan, 2021


Photo Credit PHL (Public Health Image Library) 


While it seemed obvious to many observers from very early in the pandemic (see April 2020's COVID-19: The Airborne Division) that the SARS-CoV-2 virus was airborne - making masks and indoor ventilation important safety measures - many governments and public health agencies were very slow to embrace the idea. 

An `airborne'virus' - some reasoned - would greatly complicate the response, require more expensive countermeasures, and might dissuade some front-line personnel from working without protective gear (which was in short supply).

After the SARS outbreak of 2003, and the experiences at the Amoy Gardens Apartment in Hong Kong where 330+ residents were infected, there were already suspicions that SARS could be spread via aerosols.  

The CDC's (archived) Severe Acute Respiratory Syndrome (SARS) website (updated May, 2005) had this to say about the transmission of SARS.
Transmission of SARS-CoV appears to occur predominantly through close interactions with infected persons. Infectious respiratory secretions are the most likely source of infection, although fecal/oral transmission may have occurred in some settings.
Contact with contaminated body substances, either directly (e.g., shaking hands) or indirectly (e.g., touching objects contaminated with respiratory secretions or stool), can lead to exposure. SARS-CoV may also be transmitted through close contact with respiratory droplets expelled when a patient coughs or sneezes. In some instances, however, true airborne transmission (i.e., via droplet nuclei) cannot be excluded as a possible mode of SARS-CoV transmission. 

In February of 2020, the rapid spread of the virus aboard the Diamond Princess cruise ship in Japan strongly suggested airborne spread (see CDC HAN #00430: Guidance about Global Travel on Cruise Ships).

In the months that followed and we saw a number of `super spreading' events in restaurants, churches, and other large gatherings.

Environmental studies consistently found evidence of SARS-CoV-2 contamination in rooms occupied by infected patients (even asymptomatic cases), and often many yards away, either carried by air drafts or transferred by people and/or materials that had close contact with an infected person. 

EID Journal: Prolonged Infectivity of SARS-CoV-2 in Fomites

EID Journal: Persistence of SARS-CoV-2 in Aerosol Suspensions

EID Journal: Detection of SARS-CoV-2 on Surfaces in Quarantine Rooms

EID Journal: Aerosol and Surface Distribution of SARS-CoV-2 in Hospital Wards, Wuhan, China

In July of 2020, 200+ scientists from around the world signed an open letter to the WHO, urging them to reconsider their stance on the airborne spread of the virus. But a month later - more than 8 months into the pandemic - the `debate' over the aerosol transmission of SARS-CoV-2 still raged (see BMJ Editorial: Airborne Transmission of Covid-19).

This failure to recognize the obvious led to delays in recommending face masks for the public, and N95s for 1st responders, both of which put lives at risk.
It would take nearly a year before major public health agencies would prioritize increasing building ventilation and air filtration (see ECDC: Heating, Ventilation and Air-conditioning Systems in the Context of COVID-19: 1st update).

While the airborne transmission of COVID is now accepted, we can't afford to go through the same painful period of denial when the next pandemic threat appears.  

Hopefully, the following report published this week in the CDC's EID Journal - illustrating how easily COVID spread between floors at a quarantine hotel in Taiwan - will help guide our decision making in the future. 

Probable Aerosol Transmission of SARS-CoV-2 through Floors and Walls of Quarantine Hotel, Taiwan, 2021

Author affiliations: Taiwan Centers for Disease Control, Ministry of Health and Welfare, Taipei, Taiwan (H.-Y. Wei, M.-T. Liu, J.-J. Mu, Y.-J. Lin, C.-p. Su); Chang Jung Christian University, Tainan, Taiwan (C.-P. Chang, Y.-T. Dai)

We investigated a cluster of SARS-CoV-2 infections in a quarantine hotel in Taiwan in December 2021. The cluster involved 3 case patients who lived in nonadjacent rooms on different floors. They had no direct contact during their stay. By direct exploration of the space above the room ceilings, we found residual tunnels, wall defects, and truncated pipes between their rooms.

We conducted a simplified tracer-gas experiment to assess the interconnection between rooms. Aerosol transmission through structural defects in floors and walls in this poorly ventilated hotel was the most likely route of virus transmission. This event demonstrates the high transmissibility of Omicron variants, even across rooms and floors, through structural defects. Our findings emphasize the importance of ventilation and integrity of building structure in quarantine facilities.


Taiwan contains the COVID-19 pandemic mainly through tight quarantine measures for inbound travelers. In the weeks leading up to Lunar New Year of 2022 (February 1, 2022), there were strong demands for quarantine hotels because many overseas residents of Taiwan traveled back home. Consequently, many commercial hotels were adapted for use as quarantine hotels, although they were not designed for that purpose. Increased spread of the Omicron variant through aerosol transmission posed great risk for residents of these hotels, despite stringent quarantine

The first outbreak of SARS-CoV-2 in a quarantine hotel in Taiwan was detected in December 2021. The outbreak affected 8 travelers and involved the Delta variant (9). Since then, 15 or more clusters of Omicron variant transmission have occurred within quarantine hotels; all clusters were confirmed by whole-genome sequencing (10,11). Previous reports in other countries likewise have revealed that aerosol transmission can happen across corridors (1214) and floors (1518) of quarantine hotels and apartments. Nonetheless, the relationship between disease transmission and building structure and ventilation remains largely unexplored.

On December 29, 2021, three cases of COVID-19 associated with a quarantine hotel in northern Taiwan were reported to the Taiwan Centers for Disease Control. The 3 patients stayed in nonadjacent rooms across floors and were diagnosed with COVID-19 during their quarantine period. The Taiwan Centers for Disease Control initiated an investigation to identify the infection source and possible transmission route and to recommend preventive measures.



We conclude that an episode of SARS-CoV-2 Omicron variant transmission occurred in the quarantine hotel we studied in Taipei City, Taiwan. It was the first domestic cluster of Omicron variant in Taiwan. The case-patients had stayed in different rooms and even on different floors. They had no direct contact with each other during their stay. The Omicron variant is highly transmissible (2527), so aerosol transmission was the most plausible route in this investigation of what we determined to be a poorly ventilated quarantine hotel. The special setting of this and other quarantine hotels (that is, facilities used to place persons in closed and separated rooms) provided a unique opportunity to see that the highly transmissible Omicron variant can cause infections between floors and through wall defects.


Our findings support the possibility of SARS-CoV-2 aerosol transmission in a poorly ventilated quarantine hotel, which underscores the importance of ventilation and the integrity of building structure in selecting and approving quarantine facilities. To improve ventilation, a quarantine hotel should maintain a fresh air supply, and the exhaust gas from each quarantine unit must be properly collected and discharged. The building structure of a quarantine facility should be inspected to confirm that there is no gas exchange between units. The ethanol gas tracer test is a harmless, quick, and easy way to check for interconnections between rooms, a method that can be carried out by quarantine hotel personnel to confirm the integrity of rooms without requiring professional instruments or specialized techniques. To further reduce the risk for aerosol transmission in quarantine hotels, we recommend that the public health sector enhance surveillance during the quarantine period for inbound travelers, ensure good indoor ventilation, and promote public acknowledgment of aerosol transmission.

Dr. Wei is a medical officer in the Centers for Disease Control, Ministry of Health and Welfare, Taiwan. Her primary interest is infectious disease epidemiology

          (Continue . . . .)

Many of our missteps during the opening months of the COVID pandemic were forced by our lack of preparation for a severe pandemic. 

Despite years of warnings that the World was Ill-Prepared To Deal With A Pandemic, stockpiles of PPEs were poorly maintained (see Caught With Our Masks Down (Revisited), and most pandemic plans were woefully inadequate (see The Most Predicted Global Crisis of the 21st Century).

We either learn from the last 3 years of COVID, or we are doomed to repeat it.