Comparing Coronavirus Disease 2019 (COVID-19) Pandemic Waves in Hospitalized Patients: A Retrospective, Multicenter, Cohort Study

Background: Coronavirus disease 2019 was first diagnosed in Israel at the end of February 2020. By the end of June 2021, there were 842 536 confirmed cases and 6428 deaths. Our aim in this multicenter, retrospective, cohort study is to describe the demographic and clinical characteristics of hospitalized patients and compare the pandemic waves before immunization. Methods: Of 22 302 patients hospitalized in general medical centers, we randomly selected 6329 for the study. Of these, 3582 and 1106 were eligible for the study in the first period (first and second waves) and in the second period (third wave), respectively. Results: Thirty-day mortality was higher in the second period than in the first period, 25.20% vs 13.68% (P < .001). Invasive mechanical ventilation supported 9.19% and 14.21% of patients in the first period and second period, respectively. Extracorporeal membrane oxygenation (ECMO) was used more than twice as often in the second period. Conclusions: Invasive ventilation, use of ECMO, and mortality rate were 1.5 to 2 times higher in the second period than in the first period. In the second period, patients had a more severe presentation and higher mortality than those in the first period.