ABSTRACT SARS-CoV-2 nosocomial outbreaks in the first COVID-19 wave were likely associated with a shortage of personal protective equipment and scarce indications on control measures. Having covered these limitations, updates on current SARS-CoV-2 nosocomial outbreaks are required. We carried out an in-depth analysis of a 27-day nosocomial outbreak in a gastroenterology ward in our hospital, potentially involving 15 patients and 3 health care workers. Patients had stayed in one of three neighboring rooms in the ward. The severity of the infections in six of the cases and a high fatality rate made the clinicians suspect the possible involvement of a single virulent strain persisting in those rooms. Whole-genome sequencing (WGS) of the strains from 12 patients and 1 health care worker revealed an unexpected complexity. Five different SARS-CoV-2 strains were identified, two infecting a single patient each, ruling out their relationship with the outbreak; the remaining three strains were involved in three independent, overlapping, limited transmission clusters with three, three, and five cases. Whole-genome sequencing was key to understand the complexity of this outbreak. IMPORTANCE We report a complex epidemiological scenario of a nosocomial COVID-19 outbreak in the second wave, based on WGS analysis. Initially, standard epidemiological findings led to the assumption of a homogeneous outbreak caused by a single SARS-CoV-2 strain. The discriminatory power of WGS offered a strikingly different perspective consisting of five introductions of different strains, with only half of them causing secondary cases in three independent overlapping clusters. Our study exemplifies how complex the SARS-CoV-2 transmission in the nosocomial setting during the second COVID-19 wave occurred and leads to extending the analysis of outbreaks beyond the initial epidemiological assumptions.
【저자키워드】 COVID-19, SARS-CoV-2, Genomic epidemiology, Nosocomial transmission, 【초록키워드】 Personal protective equipment, severity, hospital, health care workers, nosocomial, Sequencing, Infection, Transmission, gastroenterology, Health, Measures, outbreak, Patient, Clusters, nosocomial outbreak, second wave, epidemiological, WGS, Strains, Care, Analysis, strain, overlapping, clinician, Perspective, complex, indication, in-depth analysis, Fatality rate, assumption, SARS-CoV-2 strain, virulent, nosocomial COVID-19, infecting, secondary case, limitations, FIVE, independent, discriminatory power, initial, occurred, caused, carried, involved, required, homogeneous, epidemiological finding, Initially, offered, the SARS-CoV-2, transmission cluster,