The SIS NET ICU study: characteristics of patients with severe community acquired pneumonia admitted to Italian ICUs—a multicenter prospective observational study

Background: The SIS-NET ICU study aimed to describe the epidemiology of severe community-acquired pneumonia (CAP) among patients admitted to Italian intensive care units (ICUs). This study also aimed to describe the clinical and microbiological characteristics, outcomes, and treatments received by the included patients. Methods: We conducted a prospective, observational, multicenter study. We included patients consecutively admitted to the ICUs of 13 participating centers during the study period for acute respiratory failure due to CAP. The study period spanned from January to November 2025. The analyses aimed to describe the epidemiological and clinical characteristics, diagnostic pathways, factors associated with ICU mortality, and type of respiratory support during the ICU stay. Results: We included a cohort of 150 patients with a mean age of 63 years and a male predominance (61%). The occurrence rate of CAP in the participating ICUs was 2.5%. Streptococcus pneumoniae, Haemophilus influenzae, Influenza A and Respiratory Syncytial Virus were the predominant isolated microorganisms. The average APACHE II score was 17 (SD 7.9) and the median SOFA score was 7 (SD 3.9). The comorbidity burden was substantial. A high proportion of patients was managed with non-invasive respiratory supports. Rapid microbiological testing methods were early adopted in 63% of patients, with substantial impact on antimicrobial therapy decisions. Each 10-year increase in age was associated with a 54% increase in the odds of death (aOR 1.54, 95% CI 1.06-2.35; p = 0.02) and immunosuppressed status was associated with higher odds of death (aOR 3.13, 95% CI 1.04-9.63; p = 0.04). Polymicrobial infection showed a trend towards higher mortality (aOR 2.47, 95% CI 0.94-6.89; p = 0.06), although this association did not reach conventional statistical significance. Conclusions: Our study demonstrated the predominance of common pathogens as microbiological isolates in patients with severe CAP in Italy. Age, and immunosuppressed status were independently associated with a higher odds of mortality.