To prevent SARS‐CoV‐2 transmission in designated quarantine hotel for travelers: Is the ventilation system a concern?

To control the spread of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), the causative agent of coronavirus disease 2019 (COVID‐19), travel restriction, border control, and quarantine measures have been implemented in many countries to minimize the importation of COVID‐19,¹ especially with the emerging SARS‐CoV‐2 variants.² In Hong Kong, persons returning from mainland China have to undergo compulsory home quarantine for 14 days since 8 February 2020, and nucleic acid testing (NAT) for SARS‐CoV‐2 for inbound travelers at the Hong Kong International Airport (HKIA) has been implemented since 20 March 2020.³ Despite these, community outbreak of COVID‐19 due to imported cases still occurred.⁴ Starting from 25 December 2020, mandatory quarantine in designated hotels for 21 days was imposed on persons returning from all countries except mainland China.⁵ In addition, these persons are required to produce a negative SARS‐CoV‐2 test result within 72 h before boarding, and to be tested again at the HKIA.

Infection control training has been provided to staff serving returned travelers, including instructions on proper donning and doffing of full personal protective equipment, similar to the requirement for healthcare workers in hospitals. In the quarantine hotels, residents are not allowed to leave the rooms. Meals are delivered and waste is placed outside the doors without direct interaction between residents and staff. The communal areas, such as floors and walls of corridors, are disinfected with sodium hypochlorite (1000 ppm) at least three times a day. NAT for SARS‐CoV‐2 is performed on the 12th and 19th day of quarantine. Blood test is not performed for the detection of SARS‐CoV‐2 antibodies during the quarantine period. A designated team of two trained‐persons is responsible for collecting nasal and throat swabs for each resident. A portable high‐efficiency particulate air (HEPA) filter is placed outside the door during the collection of specimens. Residents tested positive for SARS‐CoV‐2 will be admitted to airborne infection isolation unit in public hospitals or community isolation and treatment facilities to minimize the risk of COVID‐19 outbreak.⁶, ⁷ These quarantine measures have successfully prevented community transmission of SARS‐CoV‐2 variants so far.

However, two asymptomatic COVID‐19 patients with SARS‐CoV‐2 variants were reported 8 and 9 days after checking out from two quarantine hotels (Hotels R1 and R2) of similar ventilation design in April 2021. There was no epidemiological link suggestive of SARS‐CoV‐2 acquisition in the community, and the two patients had no contact with staff or other residents during quarantine after reviewing the closed‐circuit television. In addition, all staff in the hotels were tested negative for SARS‐CoV‐2. However, there were confirmed cases infected with SARS‐CoV‐2 variants staying in the adjacent rooms on the same floor. We conducted on‐site investigation in Hotels R1 and R2. There was no recognized lapse in infection control measures among staff in either hotel. Assessment of ventilation system revealed a lack of an exhaust air system in the corridors, which was ventilated with 100% recirculated air from the fan coil unit. In the guest rooms, toilet exhaust fan generated negative pressure to draw airflow from the corridors to guest rooms then into the toilets, provided that all windows were closed. There were no fresh air supply ducts in both the corridors and guest rooms. Fresh air entry into the premises was by diffusion from outdoors or through the open windows in the guest rooms. In Hotel R1, the measured air changes per hour in the guest room (18 square meters) was 2.4. Using smoke test, we showed that the direction of airflow may reverse from room‐to‐corridor instead of corridor‐to‐room when the doors and windows were opened. When simulating nasal‐throat swabbing, the smoke was not completely removed by the portable HEPA filter and leaked out to the corridor. If virus‐laden aerosols leaked out from guest rooms occupied by infected patients to the corridors in a similar fashion, other residents may inhale the aerosols when opening the door without wearing a surgical mask. Wearing surgical masks could reduce but not completely eliminate the risk of infection. In addition, the virus‐laden aerosols may enter other guest rooms when drawn by the negative pressure generated by the toilet exhaust fan as described above, or diffuse through the cracks between doors and frames. Therefore, airborne transmission may occur in hotels due to lack of fresh air supply in both guest rooms and corridors, disorderly airflow, and relatively stagnant air in communal areas. Although other route of transmission could not be completely ruled out, or the cases may have been missed due to sampling error on day 12 and 19, the ventilation issue is still worth exploring. Improving the ventilation design in quarantine hotels can be considered as a preemptive measure to prevent airborne transmission within the hotels. In fact, transmission of COVID‐19 in quarantine hotels for travelers have been reported in the news (Table S1). Investigations did not reveal the route of transmission in most cases, but airborne transmission was implicated in a few incidents.

Our experience has implications on the design and workflow of quarantine hotels for COVID‐19. Firstly, the ventilation system of most hotels is not built for quarantine purpose. A confirmed case may stay in the room for days before the diagnosis, thus increasing the risk of transmission at the quarantine venue. More frequent SARS‐CoV‐2 testing on day 3 and 7, in addition to day 12 and 19, may increase the yield,⁸ and shorten the diagnostic window and length of stay in the hotels. Secondly, it may not be possible to increase the fresh air supply to the hotel premises or install higher‐grade filter in the hotel ventilation system. Alternatively, portable air purifiers with HEPA filters should be considered, at least in the corridor of each floor, and ideally in each room. Thirdly, alternate rooms instead of adjacent and opposite rooms should be utilized to reduce the risk of door‐to‐door transmission. Fourthly, residents are advised to close the windows before opening the doors to avoid unpredicted direction of airflow, and to wear surgical mask for mutual protection while the doors are opened.⁹, ¹⁰ As airborne transmission of COVID‐19 has been recognized by World Health Organization and Centers for Disease Control and Prevention,¹¹, ¹² indoor air ventilation will be an important focus of research in SARS‐CoV‐2 transmission in the future.

CONFLICT OF INTEREST

No conflict of interest declared.

AUTHOR CONTRIBUTION

Shuk‐Ching Wong: conceptualization (equal), data curation (equal), investigation (equal), writing the original draft (equal), writing, review, and editing (equal). Hong Chen and David Christopher Lung: investigation (equal), writing, review, and editing (equal). Pak‐Leung Ho: writing, review, and editing (equal). Kwok‐Yung Yuen: conceptualization (equal), investigation (equal), writing, review, and editing (equal). Vincent Chi‐Chung Cheng: conceptualization (equal), data curation (equal), investigation (equal), and writing the original draft (equal), as well as writing, review, and editing (equal).

Supporting information

Table S1