Comparison between the first and second COVID-19 waves in Internal Medicine wards in Milan, Italy: a retrospective observational study.

COVID-19 spread in two pandemic waves in Italy between 2020 and 2021. The aim of this study is to compare the first with the second COVID-19 wave, analyzing modifiable and non-modifiable factors and how these factors affected mortality in patients hospitalized in Internal Medicine wards. Consecutive patients with SARS-CoV-2 infection and dyspnea requiring O supplementation were included. The severity of lung involvement was categorized according to the patients' oxygen need. Six hundred and ten SARS-CoV-2 hospitalized patients satisfied the inclusion criteria. The overall estimated 4-week mortality was similar in the two pandemic waves. Several variables were associated with mortality after univariate analysis, but they lacked the significance after multivariable adjustment. Steroids did not exert any protective effect when analyzed in time-dependent models in the whole sample; however, steroids seemed to exert a protective effect in more severe patients. When analyzing the progression to different states of O supplementation during hospital stay, mortality was almost exclusively associated with the use of high-flow O or CPAP. The analysis of the transition from one state to the other by Cox-Markov models confirmed that age and the severity of lung involvement at admission, along with fever, were relevant factor for mortality or progression.