Nosocomial COVID-19 infections in Belgian hospitals: A longitudinal study

Introduction: COVID-19 has posed an immense burden on healthcare systems. Objectives: The objective of this study was to estimate the proportion of nosocomial infections in the Belgian hospitals since the start of the pandemic, as well as the main characteristics of patients involved. Methods: Surveillance data were extracted from the Clinical Hospital Surveillance established by Sciensano (ca 66% coverage, March 2020-March 2021, n = 51,293). European Centres for Disease Control and Prevention (ECDC) definitions for nosocomial COVID19 were applied;out-of-hospital: d14 after admission. Logistic regression was used to identify risk factors for mortality. Results: Inclusion criteria (dates of admission, diagnosis and/or sympton onset) were met for 49,623 patients (median age 72, IQR 57-83). 22,445 observations (45.23%) were tested due to symptoms indicative of a COVID-19 infection, 7868 (15.86%) due to systematic screening, 1042 (2.1%) for reasons described as 'other', and for 18,268 (36.81%) as 'unknown'. 7076 observations (14.26%) were considered asymptomatic, 23,533 (47.42%) had fever-related symptoms, 3819 (7.7%) upper respiratory, 30,782 (62.03%) lower respiratory symptoms, 2656 (5.35%) had anosmia, 11,147 (22.46%) gastro-intestinal symptoms, and 11,147 (22.46%) symptoms associated with a viral syndrome. Of all COVID infections (n = 5486, 11.0%), 1270 (2.6%), 1563 (3.1%), and 2653 (5.3%) were identified as indeterminate, probably nosocomial, and definitely nosocomial, respectively (Fig). The odds ratio (OR) of in-hospital mortality, comparing (probably + definitely) nosocomial to community acquired (out-of-hospital + indeterminate) COVID, for the entire studied population was 1.62 (95%CI 1.50-1.75). Significant increase in risk was seen only for age categories 40-59 (3.13;2.18-4.50) and 60-79 (1.5;1.32-1.71). Conclusion: Determining origin infection due to the ambiguousness around incubation periods, asymptomatic transmission and viral load over time needs further research. The proportion of nosocomial cases after the second wave emphasizes the need to further investigate the compliance of infection prevention measures over long periods. (Figure Presented).