Explosive nosocomial outbreak of SARS-CoV-2 in a rehabilitation clinic: the limits of genomics for outbreak reconstruction

M Abbas; T Robalo Nunes; A Cori; S Cordey; F Laubscher; S Baggio; T Jombart; A Iten; L Vieux; D Teixeira; M Perez; D Pittet; E Frangos; C E Graf; W Zingg; S Harbarth

doi:10.1016/j.jhin.2021.07.013

Explosive nosocomial outbreak of SARS-CoV-2 in a rehabilitation clinic: the limits of genomics for outbreak reconstruction

J Hosp Infect. 2021 Nov:117:124-134. doi: 10.1016/j.jhin.2021.07.013. Epub 2021 Aug 27.

Authors

M Abbas¹, T Robalo Nunes², A Cori³, S Cordey⁴, F Laubscher⁵, S Baggio⁶, T Jombart⁷, A Iten⁸, L Vieux⁹, D Teixeira⁸, M Perez⁸, D Pittet¹⁰, E Frangos¹¹, C E Graf¹², W Zingg¹³, S Harbarth¹⁰

Affiliations

¹ Infection Control Programme, Geneva University Hospitals, Geneva, Switzerland; MRC Centre for Global Infectious Disease Analysis, Imperial College London, London, UK. Electronic address: mohamed.abbas@hcuge.ch.
² Infection Control Programme, Geneva University Hospitals, Geneva, Switzerland; Serviço de Infecciologia, Hospital Garcia de Orta, EPE, Almada, Portugal.
³ MRC Centre for Global Infectious Disease Analysis, Imperial College London, London, UK; The Abdul Latif Jameel Institute for Disease and Emergency Analytics, School of Public Health, Imperial College London, London, UK.
⁴ Laboratory of Virology, Department of Diagnostics, Geneva University Hospitals, Geneva, Switzerland; Faculty of Medicine, University of Geneva, Geneva, Switzerland.
⁵ Laboratory of Virology, Department of Diagnostics, Geneva University Hospitals, Geneva, Switzerland.
⁶ Division of Prison Health, Geneva University Hospitals, Geneva, Switzerland; Office of Correction, Department of Justice and Home Affairs of the Canton of Zurich, Zurich, Switzerland.
⁷ The Abdul Latif Jameel Institute for Disease and Emergency Analytics, School of Public Health, Imperial College London, London, UK; Centre for Mathematical Modelling of Infectious Diseases, Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, UK.
⁸ Infection Control Programme, Geneva University Hospitals, Geneva, Switzerland.
⁹ Occupational Health Service, Geneva University Hospitals, Geneva, Switzerland.
¹⁰ Infection Control Programme, Geneva University Hospitals, Geneva, Switzerland; Faculty of Medicine, University of Geneva, Geneva, Switzerland.
¹¹ Clinique de Joli-Mont, Department of Rehabilitation and Geriatrics, Geneva University Hospitals, Geneva, Switzerland.
¹² Department of Rehabilitation and Geriatrics, Geneva University Hospitals, Geneva, Switzerland.
¹³ Infection Control Programme, Geneva University Hospitals, Geneva, Switzerland; Infection Control Programme, Zurich University Hospital, Zurich, Switzerland.

Abstract

Background: Nosocomial outbreaks of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) are frequent despite implementation of conventional infection control measures. An outbreak investigation was undertaken using advanced genomic and statistical techniques to reconstruct likely transmission chains and assess the role of healthcare workers (HCWs) in SARS-CoV-2 transmission.

Methods: A nosocomial SARS-CoV-2 outbreak in a university-affiliated rehabilitation clinic was investigated, involving patients and HCWs, with high coverage of pathogen whole-genome sequences (WGS). The time-varying reproduction number from epidemiological data (R_t) was estimated, and maximum likelihood phylogeny was used to assess genetic diversity of the pathogen. Genomic and epidemiological data were combined into a Bayesian framework to model the directionality of transmission, and a case-control study was performed to investigate risk factors for nosocomial SARS-CoV-2 acquisition in patients.

Findings: The outbreak lasted from 14^th March to 12^th April 2020, and involved 37 patients (31 with WGS) and 39 employees (31 with WGS), 37 of whom were HCWs. Peak R_t was estimated to be between 2.2 and 3.6. The phylogenetic tree showed very limited genetic diversity, with 60 of 62 (96.7%) isolates forming one large cluster of identical genomes. Despite the resulting uncertainty in reconstructed transmission events, the analyses suggest that HCWs (one of whom was the index case) played an essential role in cross-transmission, with a significantly greater fraction of infections (P<2.2e-16) attributable to HCWs (70.7%) than expected given the number of HCW cases (46.7%). The excess of transmission from HCWs was higher when considering infection of patients [79.0%; 95% confidence interval (CI) 78.5-79.5%] and frail patients (Clinical Frailty Scale score >5; 82.3%; 95% CI 81.8-83.4%). Furthermore, frail patients were found to be at greater risk for nosocomial COVID-19 than other patients (adjusted odds ratio 6.94, 95% CI 2.13-22.57).

Interpretation: This outbreak report highlights the essential role of HCWs in SARS-CoV-2 transmission dynamics in healthcare settings. Limited genetic diversity in pathogen genomes hampered the reconstruction of individual transmission events, resulting in substantial uncertainty in who infected whom. However, this study shows that despite such uncertainty, significant transmission patterns can be observed.

Keywords: COVID-19; Healthcare-associated infection; Infection prevention and control; Long-term care facilities; Nosocomial outbreaks; SARS-CoV-2.

MeSH terms

Bayes Theorem
COVID-19*
Case-Control Studies
Cross Infection* / epidemiology
Disease Outbreaks
Explosive Agents*
Genomics
Health Personnel
Humans
Phylogeny
SARS-CoV-2

Substances

Explosive Agents

Abstract

MeSH terms

Substances

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