Epidemiology and outcome of intra-abdominal infections in intensive care unit in Italy from the Italian Register of complicated Intra-abdominal InfectionS—the IRIS study: a prospective observational nationwide study

Background: Intra-abdominal infections are complex and potentially life-threatening conditions frequently requiring intensive care admission and are associated with highly variable mortality driven by disease severity, host response, comorbidities, and antimicrobial resistance. Outcomes depend on timely diagnosis, effective surgical source control, appropriate antimicrobial therapy, and a coordinated multidisciplinary approach addressing both the infectious and systemic inflammatory components of the disease. Material and method: This was a prospective, observational nationwide study. We included all adult patients admitted to the hospital with complicated abdominal infections requiring ICU admission. The aim of this study was to describe the epidemiology and outcomes of patients admitted to the hospital with intra-abdominal infections (IAIs) requiring an intensive care unit (ICU) admission in 23 Italian hospitals. Results: A total of 784 patients admitted to the hospital with complicated IAIs requiring ICU admission were enrolled. Overall, in-hospital mortality among ICU patients was 23.9%. Septic shock (36.2%) and sepsis (35.9%) were the main reasons for ICU admission. Community-acquired infections accounted for 64.8% of cases, and adequate source control was achieved in 61.5% of patients. Re-operation was required in 21%. The most frequently isolated pathogens were Escherichia coli (23.1%), followed by Enterococcus spp. (15.4%). Empiric antibiotic therapy was prescribed in more than 80% of patients (median duration ranging from 8.1 to 19.3 days). Piperacillin-tazobactam was the most commonly used antibiotic. In multivariable logistic regression analysis, increasing age (OR 1.04 per year, 95% CI 1.03-1.06), immunosuppression (OR 1.99, 95% CI 1.09-3.66), serious cardiovascular disease (OR 1.91, 95% CI 1.20-3.05), re-operation (OR 2.30, 95% CI 1.34-3.96), inadequate source control (OR 0.39, 95% CI 0.22-0.71), peritonitis (OR 0.39, 95% CI 0.23-0.66), and healthcare-associated infections (OR 1.83, 95% CI 1.10-3.04) were independently associated with in-hospital mortality. Duration of antibiotic therapy, malignancy, and delay in initial intervention were not significantly associated with mortality. Conclusion: Septic shock remains the leading cause of ICU admission in patients with IAIs. Patients with immunosuppression, serious cardiovascular comorbidities, requirement for re-operation, inadequate source control, peritonitis, and healthcare-associated infections were at significantly higher risk of in-hospital mortality. Overall, our study reinforces the multifactorial nature of mortality in critically ill patients with intra-abdominal infections, highlighting modifiable factors (source control, timely intervention) that can be targeted to improve outcomes.