Risk Factors for Admission into COVID-19 General Wards, Sub-Intensive and Intensive Care Units among SARS-CoV-2 Positive Subjects in the Municipality of Bologna, Italy

This is a retrospective cohort study aimed at identifying the risk factors for the hospitalization of patients with COVID-19 in the municipality of Bologna. A total of 32500 patients that tested positive for COVID-19 from February 28/2020 to October 13/2021 in the municipality of Bologna were included. The Kaplan-Meier method was used to estimate changes during time of ICU hospitalization for all patients as well as stratifying subjects by sex. A multi-state Cox’s proportional hazard model was fitted to investigate predictors of ICU and non-ICU hospitalization. Age, sex, calendar period of diagnosis, comorbidities and vaccination status of patients at the time of diagnosis were considered as candidate predictors. In general, male sex and advanced age resulted to be poor prognostic factors of COVID-19 outcomes. An exception was found for the over 80 age group which showed a decrease in the risk of ICU hospitalization compared to 70-79 (HR 0.57 95% CI 0.36 - 0.90 for DIAG → ICU; HR 0.40 95% CI 0.28 - 0.58 for HOSP → ICU). Having contracted the disease during the first wave was associated with a significant greater risk of hospitalization than during the second wave, while no difference in the risk of ICU admission was found between the second and third waves. Fully immunized patients showed a significant decrease in the risk of ICU and non-ICU hospitalization compared to the unvaccinated patients (HR 0.23 95% CI 0.16 - 0.31 for DIAG → HOSP; HR 0.10 95% CI 0.01 - 0.73 for DIAG → ICU). Chronic kidney failure and asthma were risk factors for non-ICU hospitalization. Diabetes and embolism were risk factors for both direct ICU and non-ICU hospitalization. The study of factors associated with a negative course of the COVID-19 disease allows to prevent fatal outcomes, establish priorities in the treatment of the disease and improve the management of hospital resources and the pandemic itself. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The authors received no specific funding for this work ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethical approval for the study was obtained from the University of Bologna's Ethical Committee (approval number 283066, 5 October 2021). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data of the present study were provided from the Local Health Unit (AUSL, Azienda 385 Unit`a Sanitaria Locale) of the municipality of Bologna, Italy, and the authors do not 386 have the right to share them. In order to gain access to the data, contact Local Health 387 Unit of the municipality of Bologna, Italy (paolo.tubertini{at}aosp.bo.it).