Immunocompromised patients with viral severe acute respiratory infection in intensive care: an Australia wide, retrospective, observational study

BACKGROUND: The aim of this study was to compare the clinical characteristics, treatments and outcomes of immunocompromised patients with viral severe acute respiratory infections (SARI), to those of immunocompetent patients admitted to an intensive care unit (ICU) across Australia. METHODS: Retrospective analysis of a prospective, nation-wide, observational registry of 46 ICUs from June 2022 to August 2025. Critically ill adults (age ≥ 18) with laboratory-confirmed viral SARI were included. Immunocompromised status was defined by the presence of any one of the following: chronic immunosuppression, malignant neoplasm, AIDS/HIV, or organ transplantation. Associations between immunocompromised status and in-hospital mortality were evaluated using mixed-effects logistic regression models. Competing risks regression (Fine and Gray models) was used to assess the association between immunocompromised status and risk of hospital discharge within 30 days. RESULTS: Among 4,703 patients with viral SARI who were admitted to ICUs, immunocompromised patients accounted for 908 (19.3%) cases. Immunocompromised patients were older (median age 67 vs. 62 years), more comorbid (31.4% vs. 22.5% with ≥ 3 comorbidities), and more frequently admitted with COVID-19 (51.1% vs. 34.5%); (p < 0.001 for all). Immunocompromised patients received more treatment, including antivirals (67.3% vs. 57.7%), and corticosteroids (81.7% vs. 72%) and had higher in-hospital mortality (22.7% vs. 13.1%); (p < 0.01 for all). After adjusting for demographics, comorbidities, vaccination status (where available), ICU interventions and treatments, immunocompromised status was independently associated with nearly double the odds of in-hospital mortality (adjusted OR 1.93, 95% CI 1.57-2.37). CONCLUSIONS: In this study, we found that immunocompromised patients accounted for approximately one-fifth of critically ill viral SARI patients and had nearly twice the odds of in-hospital mortality, when compared to those that were immunocompetent. Targeted public health campaigns and improved treatment strategies may be warranted for this population.