Vincent Chi-Chung Cheng1,2, Kitty Sau-Chun Fung3, Gilman Kit-Hang Siu4, Shuk-Ching Wong1, Lily Shui-Kuen Cheng3, Man-Sing Wong5, Lam-Kwong Lee4, Wan-Mui Chan6, Ka-Yee Chau3, Jake Siu-Lun Leung4, Allen Wing-Ho Chu6, Wai-Shan Chan3, Kelvin Keru Lu4, Kingsley King-Gee Tam6, Jonathan Daniel Ip6, Kenneth Siu-Sing Leung6, David Christopher Lung7, Herman Tse8, Kelvin Kai-Wang To6, Kwok-Yung Yuen6. 1. Infection Control Team, Queen Mary Hospital, Hong Kong West Cluster, Hong Kong Special Administrative Region, China. 2. Department of Microbiology, Queen Mary Hospital, Hong Kong Special Administrative Region, China. 3. Department of Pathology and Infection Control Team, United Christian Hospital, Hong Kong Special Administrative Region, China. 4. Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Hong Kong Special Administrative Region, China. 5. Department of Land Surveying and Geo-Informatics, The Hong Kong Polytechnic University, Hong Kong Special Administrative Region, China. 6. Department of Microbiology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China. 7. Department of Pathology, Hong Kong Children's Hospital / Queen Elizabeth Hospital, Hong Kong Special Administrative Region, China. 8. Department of Pathology, Hong Kong Children's Hospital, Hong Kong Special Administrative Region, China.
Abstract
BACKGROUND: Nosocomial outbreaks with superspreading of COVID-19 due to a possible airborne transmission has not been reported. METHODS: Epidemiological analysis, environmental samplings, and whole genome sequencing (WGS) were performed for a hospital outbreak. RESULTS: A superspreading event involving 12 patients and 9 healthcare workers (HCWs) occurred within 4 days in 3 of 6 cubicles at an old-fashioned general ward with no air exhaust built within the cubicles. The environmental contamination by SARS-CoV-2 RNA was significantly higher in air grilles (>2m from patients' head and not reachable by hands) than high-touch clinical surfaces (36.4%, 8/22 vs 3.4%, 1/29, p=0.003). Six (66.7%) of 9 contaminated air exhaust grilles were located outside patient cubicle. The clinical attack rate of patients was significantly higher than HCWs (15.4%, 12/78 exposed-patients vs 4.6%, 9/195 exposed-HCWs, p=0.005). Moreover, clinical attack rate of ward-based HCWs was significantly higher than non-ward-based HCWs (8.1%, 7/68 vs 1.8%, 2/109, p=0.045). The episodes (mean ± S.D) of patient-care duty assignment in the cubicles was significantly higher among infected ward-based HCWs than non-infected ward-based HCWs (6.0±2.4 vs 3.0±2.9, p=0.012) 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. CONCLUSION: This nosocomial point source superspreading due to possible airborne transmission demonstrated the need for stringent SARS-CoV-2 screening at admission to healthcare facilities and better architectural design of the ventilation system to prevent such outbreaks. Portable high-efficiency particulate filters were installed in each cubicle to improve ventilation before resumption of clinical service.
BACKGROUND: Nosocomial outbreaks with superspreading of COVID-19 due to a possible airborne transmission has not been reported. METHODS: Epidemiological analysis, environmental samplings, and whole genome sequencing (WGS) were performed for a hospital outbreak. RESULTS: A superspreading event involving 12 patients and 9 healthcare workers (HCWs) occurred within 4 days in 3 of 6 cubicles at an old-fashioned general ward with no air exhaust built within the cubicles. The environmental contamination by SARS-CoV-2 RNA was significantly higher in air grilles (>2m from patients' head and not reachable by hands) than high-touch clinical surfaces (36.4%, 8/22 vs 3.4%, 1/29, p=0.003). Six (66.7%) of 9 contaminated air exhaust grilles were located outside patient cubicle. The clinical attack rate of patients was significantly higher than HCWs (15.4%, 12/78 exposed-patients vs 4.6%, 9/195 exposed-HCWs, p=0.005). Moreover, clinical attack rate of ward-based HCWs was significantly higher than non-ward-based HCWs (8.1%, 7/68 vs 1.8%, 2/109, p=0.045). The episodes (mean ± S.D) of patient-care duty assignment in the cubicles was significantly higher among infected ward-based HCWs than non-infected ward-based HCWs (6.0±2.4 vs 3.0±2.9, p=0.012) 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. CONCLUSION: This nosocomial point source superspreading due to possible airborne transmission demonstrated the need for stringent SARS-CoV-2 screening at admission to healthcare facilities and better architectural design of the ventilation system to prevent such outbreaks. Portable high-efficiency particulate filters were installed in each cubicle to improve ventilation before resumption of clinical service.
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