Systemic immune-inflammation index as a dynamic marker of therapeutic response in neonatal early-onset sepsis: implications for antibiotic stewardship.

UNLABELLED: This study investigates the systemic immune-inflammation index (SII) as a dynamic marker to track antibiotic efficacy and guide stewardship in term neonates. A retrospective cohort study evaluated 275 term neonates (85 with culture-proven early-onset sepsis [EOS] and 190 controls). Complete blood counts and C-reactive protein (CRP) were analyzed on Days 1 and 3 of therapy. At diagnosis, the calculated SII was significantly higher in the EOS group compared to controls (Median 812 [IQR: 650-1120] vs. 515 [IQR: 410-630]; p < 0.001). ROC analysis yielded an AUC of 0.87. Multivariable logistic regression confirmed the independent prognostic value of the SII after adjusting for clinical confounders. By Day 3, the SII demonstrated a faster kinetic decline than CRP in 74.1% of the sepsis cohort, functioning as an early indicator of resolving inflammation.

CONCLUSION: While diagnostic accuracy at onset is comparable to CRP, the SII demonstrates potential as a practical dynamic indicator of therapeutic response in EOS. Its clinical application provides an objective biological signal that may help identify rapid responders, potentially supporting safely shortened antibiotic courses pending prospective validation.

WHAT IS KNOWN: • CRP has a delayed kinetic rise and clearance in neonatal EOS, limiting real-time monitoring. • Prolonged empirical antibiotics in neonates alter the microbiome and increase nosocomial risks.

WHAT IS NEW: • SII is an accessible, zero-cost, and dynamic indicator of therapeutic response in neonatal EOS. • A 72-hour SII reduction identifies rapid responders early, guiding safer antibiotic cessation.