Work

Association between systemic immune-inflammation index and ICU-acquired infection in critically Ill patients without infection: a competing risks analysis from a retrospective cohort

Year: 2026

Type: article

Abstract: BACKGROUND: Healthcare-associated infections and their complications represent a predominant cause of morbidity and mortality in intensive care units (ICUs) globally. Several studies have reported that the systemic immune-inflammation index (SII) is associated with an increased risk of infection; however, its association with ICU-acquired infection (ICU-AI) remains unclear. We aimed to examine the association between SII and the subsequent risk of ICU-AI. METHODS: We conducted a retrospective cohort study using the MIMIC-IV database, including adult ICU patients without suspected infection at baseline. SII was calculated as platelet × neutrophil / lymphocyte count, based on values from the first 24 h of ICU admission. The primary outcome was ICU-AI, defined as suspected infection occurring after 48 h of ICU admission. Two competing risk regression models were employed to evaluate the association between SII and ICU-AI. RESULTS: Among the 5,459 patients included, 627 (11.5%) developed ICU-AI. Higher SII (per 1,000-unit) was independently associated with an increased risk of ICU-AI in both models: adjusted cause-specific hazard ratio (CSHR), 1.06 (95% CI, 1.03-1.08; p < 0.001) and subdistribution hazard ratio (SHR), 1.05 (95% CI, 1.03-1.07; p < 0.001). When analyzed by quartiles, a significant dose-response relationship was observed (p for trend < 0.001). Compared with patients in the lowest quartile (Q1, SII ≤ 594 × 10⁹/L), those in Q3 (SII 1125-2201 × 10⁹/L) and Q4 (SII ≥ 2202 × 10⁹/L) showed progressively higher risks of infection, with adjusted CSHR of 1.44 (95% CI 1.11-1.86) and 1.76 (95% CI 1.37-2.26), and adjusted SHR of 1.51 (95% CI 1.17-1.93) and 1.96 (95% CI 1.54-2.49), respectively. Time-to-event curves showed distinct and consistent cumulative risk trajectories across SII quartiles. CONCLUSION: Elevated SII at ICU admission was independently associated with an increased risk of developing suspected secondary infection in infection-naïve critically ill patients.

Source: BMC Infectious Diseases

DOI: 10.1186/s12879-026-13568-0