Factors Associated with Transfer to Intensive Care in Younger Adults Hospitalized with COVID-19

Background/Objectives: While COVID-19 severity is strongly associated with older age, younger adults may also develop complications. This study investigated factors associated with transfer to ICU in hospitalized younger adults during May–December 2021. Materials and methods: Eighty-six consecutive patients aged ≥18 and <50 years were admitted to the University Multi-profile Hospital for Active Treatment of Infectious and Parasitic Diseases “Prof. Ivan Kirov”, Sofia, Bulgaria between 12 May 2021, and 7 December 2021. Results: Among 86 patients (median age 40 years; 55.8% female), common symptoms included fever (89.5%), cough (91.9%), headache (76.7%), and gastrointestinal symptoms (83.7%). Laboratory abnormalities were frequent: lymphopenia (median 0.94 × 109/L), elevated CRP (28.9 mg/L), LDH (333 U/L), and ferritin (198.5 µg/L). Severe andcritical disease occurred in 17.5% of cases, with 43% requiring oxygen therapy. In descriptive/univariate analyses, ICU transfer was more frequent among patients with hypoxemia (SaO2 < 90%) and higher CRP, D-dimer, vomiting and ferritin. In a Firth penalized logistic regression model (rare-event setting), endocrine/metabolic comorbidity showed a directionally consistent association with ICU transfer; gastrointestinal comorbidity signals were not interpretable because of extremely small cell counts. Conclusions: Younger adults usually present with mild to moderate COVID-19; however, a substantial minority develop severe illness. Hypoxemia and elevated inflammatory and coagulation markers were consistently associated with worse outcomes. Endocrine/metabolic comorbidity showed the most consistent association with transfer to ICU in this cohort, although all comorbidity estimates should be interpreted cautiously, given the small number of events.