Risk factors of nosocomial Covid-19 in a French university hospital: a case- control study

Abstract

Background: During the Covid-19 pandemic, prevention strategies implemented by hospitals to reduce nosocomial transmission sometimes failed and determining transmission risk factors remains crucial. Our objective was to determine the risk factors of nosocomial Covid-19.Methods: A case-control study was conducted in a French hospital between 09/01/2020 and 01/31/2021. Adult patients hospitalized in medical or surgical units were included. Infants or patients hospitalized in ICU were excluded. Cases were patients with a nosocomial Covid-19 (clinical symptoms and RT-PCR positive for SARS-CoV-2 or RT-PCR positive for SARS-CoV-2 with Ct ≤28 more than five days after admission); controls were patients without infection (RT-PCR negative for SARS-CoV-2 more than 5 days after admission). They were matched according to length of stay before diagnosis and period of admission. Analyses were performed with a conditional logistic regression.Results: A total of 281 cases and 441 controls were included. In the bivariate analysis, cases were older (OR per 10 years: 1.22; CI95% [1.10; 1.36]), had more often shared a room (OR: 1.74; CI95% [1.25; 2.43]), had more often a risk factor of severe Covid-19 (OR: 1.94; CI95% [1.09; 3.45]), were more often hospitalized in medical units [OR: 1.59; CI95% [1.12; 2.25]), had a higher exposure to contagious health care workers (HCW; OR per 1 person.days: 1.12; CI95% [1.08; 1.17]) and contagious patients (OR per 1 person.days: 1.11; CI95% [1.08; 1.14]) than controls. In an adjusted model, risk factors of nosocomial Covid-19 were exposure to contagious HCW (aOR per 1 person.days: 1.08; CI95% [1.03; 1.14]) and exposure to contagious patients (aOR per 1 person.days: 1.10; CI95% [1.07; 1.13]).Conclusions: Exposure to contagious professionals and contagious patients are the main risk factors for nosocomial Covid-19, outweighing all other potential risk factors including the hospitalisation in double room. Prevention strategies need to be adjusted according to these results to decrease the risk of nosocomial COVID-19.Trial registrationStudy ethics approval was obtained retrospectively on 22 December 2021 (CECIC Rhône-Alpes-Auvergne, Clermont-Ferrand, IRB 5891).

Patient and ward related risk factors in a multi-ward nosocomial outbreak of COVID-19: Outbreak investigation and matched case–control study

“…The retrospective nature of our case-control study precludes conclusions There have been many reports on hospital-based outbreaks of COVID-19 [4, 25, 27-29, 31, 39, 52-56], however a strength of our report is that it incorporated a case-control study to explore contributing ward and patient-related factors to the acquisition of COVID-19, occurring in a setting without vaccination for any HCWs or patients. Our outbreak has similarities with other COVID-19 nosocomial outbreaks including unidentified cases on a ward [39,56], positive HCWs who may have sub-optimal adherence to IPC measures [52,54], and the role of multi-bedded rooms in SARS-CoV-2 transmission [27,29,31,34,35] Further, our report included patient symptoms, environmental sampling, whole genome sequencing, viral culture and has identified the novel finding of fluid and electrolyte disorders increasing the likelihood of COVID-19 acquisition.…”

“…Based on our findings, patients who spent > 50% of their admission in a multi-bedded room had 3.2 times the rate of acquiring COVID-19. Other observational studies have demonstrated that multi-bedded rooms versus one-to-two bedded rooms and the use of shared toilets were more common among nosocomial COVID-19 cases compared to controls [29,31,34,35]. The duration of time in a multi-bedded room was a major risk factor and the finding of a dose-response relationship adds epidemiologic strength of association to this finding.…”

“…Our study is one of several observational studies exploring risk factors for patient COVID-19 acquisition in hospitals [25][26][27][28][29][30][31][32]. There were several factors which were identified during this outbreak in a setting without vaccination for any HCWs or patients which may have facilitated the transmission events to occur.…”