Caroline Landelle

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).

Background: A multimodal strategy to prevent nosocomial influenza was implemented in 2015–2016 in Grenoble Alpes University Hospital. Three modalities were implemented in all units: promotion of vaccination among healthcare workers, epidemiologic surveillance and communication campaigns. Units receiving a high number of patients with influenza implemented 2 additional modalities: improvement of diagnosis capacities and systematic surgical mask use. The main objective was to assess the effectiveness of the strategy for reducing the risk of nosocomial influenza. Methods: A study was conducted retrospectively investigating 5 epidemic seasons (2014–2015 to 2018–2019) including all patients hospitalized with a positive influenza test at Grenoble Alpes University Hospital. The weekly number of nosocomial influenza cases was analyzed by Poisson regression and incidence rate ratios (IRR) were estimated. Results: A total of 1540 patients, resulting in 1559 stays, were included. There was no significant difference between the 5 influenza epidemic seasons in the units implementing only 3 measures. In the units implementing the 5 measures, there was a reduction of nosocomial influenza over the seasons when the strategy was implemented compared to the 2014–2015 epidemic season (IRR = 0.56, 95% CI = 0.23–1.34 in 2015–2016; IRR = 0.39, 95% CI = 0.19–0.81 in 2016–2017; IRR = 0.50, 95% CI = 0.24–1.03 in 2017–2018; IRR = 0.48, 95% CI = 0.23–0.97 in 2018–2019). Conclusions: Our data mainly suggested that the application of the strategy with 5 modalities, including systematic surgical mask use and rapid diagnosis, seemed to reduce by half the risk of nosocomial influenza. Further data, including medico-economic studies, are necessary to determine the opportunity of extending these measures at a larger scale.