Comparison between COVID‑19 outcomes in the first 3 waves of the pandemic: a reference hospital report.

Introduction: The course of consecutive COVID‑19 waves was influenced by medical and organizational factors.

Objectives: We aimed to assess the outcomes of patients hospitalized for COVID‑19 during the first 3 waves of the pandemic.

Patients And Methods: We performed a retrospective analysis of medical records of all COVID‑19 patients admitted to the University Hospital in Kraków, Poland, a designated COVID‑19 hospital in Małopolska province, between March 1, 2020 and May 31, 2021. The waves were defined as 1, 2, and 3, and covered the periods of March 2020 to July 2020, August 2020 to January 2021, and February 2021 to May 2021, respectively. Patients' characteristics and outcomes for waves 1 through 3 were compared.

Results: Data analyses included 5191 patients with COVID‑19. We found differences in age (mean [SD], 60.2 [17.3] years vs 62.4 [16.8] years vs 61.9 [16.1] years, respectively, for waves 1, 2, and 3; P = 0.003), sex distribution (proportion of women, 51.4% vs 44.2% vs 43.6%; P = 0.003), as well as concentrations of inflammatory markers and oxygen saturation (the lowest and the highest for wave 1, respectively; P <0.001). Hospital death rates in subsequent waves were 10.4%, 19.8%, and 20.3% (P <0.001). Despite similarities in patients' characteristics, the length of hospital and intensive care unit stay was shorter for wave 3 than for wave 2. The risk factors for in‑hospital death were: advanced age, male sex, cardiovascular or chronic kidney disease, higher C‑reactive protein level, and hospitalization during the second or third wave.

Conclusions: We identified differences in patients' clinical characteristics and outcomes between consecutive pandemic waves, which probably reflect changes in terms of COVID‑19 isolation policy, hospitalization and treatment indications, and treatment strategies.