ICU Admission and Post-Discharge Mortality in COVID-19: Different Risk Factors Across Clinical Phases

Background: Risk factors for severe COVID-19 and in-hospital mortality are well described, but it remains unclear whether the same factors predict mortality after hospital discharge. Distinguishing risk profiles across clinical phases may improve patient management and follow-up strategies. Methods: We conducted a retrospective observational cohort study of 595 adults hospitalized with PCR-confirmed SARS-CoV-2 infection in Portugal (September–November 2020). The primary outcome was all-cause mortality during hospitalization and up to 120 days post-discharge. Secondary outcomes included intensive care unit (ICU) admission, maximum disease severity (WHO Clinical Progression Scale), oxygen supplementation, and length of stay. Univariable and multivariable regression analyses were performed using logistic regression for binary outcomes and linear regression for continuous outcomes. Results: Overall mortality was 22.5%, rising from 14.1% in-hospital to 22.5% at 120-day follow-up (p < 0.001), with 37.3% of deaths occurring post-discharge. ICU admission was required in 17.6% of patients and was significantly associated with obesity (OR = 2.12, 95% CI: 1.39–3.23, p < 0.001) and male sex (OR = 1.78, 95% CI: 1.14–2.78, p = 0.010) in univariable analysis. In contrast, post-discharge mortality was associated with longer hospital stay (18.4 vs. 9.9 days, p < 0.001) and a higher prevalence of malignancy (28.0% vs. 13.1%, p = 0.032), but not with ICU admission. In multivariable logistic regression, oxygen supplementation was the strongest predictor of 120-day mortality (OR = 2.50, 95% CI: 1.38–4.51, p = 0.002). Only pulmonary diseases and obesity were independently associated with maximum disease severity. Conclusions: Risk factors for acute COVID-19 severity differ from those for post-discharge mortality. These findings support a phase-specific approach to risk stratification, suggesting that patients with obesity are at increased risk of early respiratory deterioration, while patients with malignancy may benefit from closer post-discharge follow-up regardless of ICU admission status.