Nosocomial Outbreak of Coronavirus Disease 2019 by Possible Airborne Transmission Leading to a Superspreading Event

Vincent Chi-Chung Cheng, Kitty Sau-Chun Fung, Kit Hang Siu, Shuk-Ching Wong, Lily Shui-Kuen Cheng, Man Sing Wong, Lam Kwong Lee, Wan Mui Chan, Sandy Ka-Yee Chau, Siu Lun Leung, Allen Wing-Ho Chu, Wai-Shan Chan, Keru Lu, Kingsley King-Gee Tam, Jonathan Daniel Ip, Kenneth Siu Sing Leung, David Christopher Lung, Herman Tse, Kelvin Kai Wang To, Kwok Yung Yuen

Research output: Journal article publicationJournal articleAcademic researchpeer-review

40 Citations (Scopus)


BACKGROUND: Nosocomial outbreaks with superspreading of coronavirus disease 2019 due to a possible airborne transmission have not been reported. METHODS: Epidemiological analysis, environmental samplings, and whole-genome sequencing (WGS) were performed for a hospital outbreak. RESULTS: A superspreading event that involved 12 patients and 9 healthcare workers (HCWs) occurred within 9 days in 3 of 6 cubicles at an old-fashioned general ward with no air exhaust built within the cubicles. The environmental contamination by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA was significantly higher in air grilles (>2 m from patients' heads and not within reach) than on high-touch clinical surfaces (36.4%, 8 of 22 vs 3.4%, 1 of 29, P = .003). Six (66.7%) of 9 contaminated air exhaust grilles were located outside patient cubicles. The clinical attack rate of patients was significantly higher than of HCWs (15.4%, 12 of 78 exposed patients vs 4.6%, 9 of 195 exposed HCWs, P = .005). Moreover, the clinical attack rate of ward-based HCWs was significantly higher than of nonward-based HCWs (8.1%, 7 of 68 vs 1.8%, 2 of 109, P = .045). The episodes (mean ± standard deviation) of patient-care duty assignment in the cubicles was significantly higher among infected ward-based HCWs than among noninfected ward-based HCWs (6.0 ± 2.4 vs 3.0 ± 2.9, P = .012) during the outbreak period. The outbreak strains belong to SARS-CoV-2 lineage B.1.36.27 (GISAID clade GH) with the unique S-T470N mutation on WGS. CONCLUSIONS: This nosocomial point source superspreading event due to possible airborne transmission demonstrates the need for stringent SARS-CoV-2 screening at admission to healthcare facilities and better architectural design of ventilation systems to prevent such outbreaks. Portable high-efficiency particulate filters were installed in each cubicle to improve ventilation before resumption of clinical service.

Original languageEnglish
Pages (from-to)e1356-e1364
JournalClinical Infectious Diseases
Issue number6
Publication statusPublished - 15 Sept 2021


  • COVID-19
  • airborne transmission
  • hospital outbreak
  • ventilation system
  • whole genome sequencing

ASJC Scopus subject areas

  • Microbiology (medical)
  • Infectious Diseases


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