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Observational Study
. 2022 Apr 11;17(4):e0263548.
doi: 10.1371/journal.pone.0263548. eCollection 2022.

Mortality rates among COVID-19 patients hospitalised during the first three waves of the epidemic in Milan, Italy: A prospective observational study

Andrea Giacomelli  1 , Anna Lisa Ridolfo  1 , Laura Pezzati  1   2 , Letizia Oreni  1 , Giorgia Carrozzo  1   2 , Martina Beltrami  1   2 , Andrea Poloni  1   2 , Beatrice Caloni  1   2 , Samuel Lazzarin  1   2 , Martina Colombo  1   2 , Giacomo Pozza  1   2 , Simone Pagano  1   2 , Stefania Caronni  1   2 , Chiara Fusetti  1 , Martina Gerbi  1 , Francesco Petri  1 , Fabio Borgonovo  1 , Fabiana D'Aloia  2 , Cristina Negri  1 , Giuliano Rizzardini  1 , Spinello Antinori  1   2
Affiliations
Observational Study

Mortality rates among COVID-19 patients hospitalised during the first three waves of the epidemic in Milan, Italy: A prospective observational study

Andrea Giacomelli et al. PLoS One. .

Abstract

Introduction: This paper describes how mortality among hospitalised COVID-19 patients changed during the first three waves of the epidemic in Italy.

Methods: This prospective cohort study used the Kaplan-Meier method to analyse the time-dependent probability of death of all of the patients admitted to a COVID-19 referral centre in Milan, Italy, during the three consecutive periods of: 21 February-31 July 2020 (first wave, W1), 1 August 2020-31 January 2021 (second wave, W2), and 1 February-30 April 2021 (third wave, W3). Cox models were used to examine the association between death and the period of admission after adjusting for age, biological sex, the time from symptom onset to admission, disease severity upon admission, obesity, and the comorbidity burden.

Results: Of the 2,023 COVID-19 patients admitted to our hospital during the study period, 553 (27.3%) were admitted during W1, 838 (41.5%) during W2, and 632 (31.2%) during W3. The crude mortality rate during W1, W2 and W3 was respectively 21.3%, 23.7% and 15.8%. After adjusting for potential confounders, hospitalisation during W2 or W3 was independently associated with a significantly lower risk of death than hospitalisation during W1 (adjusted hazard ratios [AHRs]: 0.75, 95% confidence interval [CI] 0.59-0.95, and 0.58, 95% CI 0.44-0.77). Among the patients aged >75 years, there was no significant difference in the probability of death during the three waves (AHRs during W2 and W3 vs W1: 0.93, 95% CI 0.65-1.33, and 0.88, 95% CI 0.59-1.32), whereas those presenting with critical disease during W2 and W3 were at significantly lower risk of dying than those admitted during W1 (AHRs 0.61, 95% CI 0.43-0.88, and 0.44, 95% CI 0.28-0.70).

Conclusions: Hospitalisation during W2 and W3 was associated with a reduced risk of COVID-19 death in comparison with W1, but there was no difference in survival probability in patients aged >75 years.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Time-dependent survival probability by period of hospital admission: Wave 1 (February-July 2020), wave 2 (August 2020-January 2021), and wave 3 (February-April 2021).
Fig 2
Fig 2. Time-dependent survival probability by period of hospital admission (wave 1 [February-July 2020], wave 2 [August 2020-January 2021], and wave 3 [February-April 2021]) stratified by age: A ≤45 years; B 46–60 years; C 61–75; and D >75 years.
Fig 3
Fig 3. Time-dependent survival probability by period of hospital admission (wave 1 [February-July 2020], wave 2 [August 2020-January 2021], and wave 3 [February-April 2021]) stratified by disease severity upon hospital admission.
A: mild/moderate disease; B: severe disease; C: critical disease.
See this image and copyright information in PMC

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