Pathophysiology
Clinical meaning
Neonatal sepsis is a systemic bloodstream infection occurring within the first 28 days of life that carries significant morbidity and mortality. The neonatal immune system is functionally immature, with several critical vulnerabilities that predispose newborns to infection. Neonates have decreased neutrophil storage pools (approximately 20% of adult capacity), reduced neutrophil chemotaxis and phagocytic killing capacity, diminished complement system activity (both classic and alternative pathways are at 50% of adult levels), low immunoglobulin production (neonates rely primarily on maternally transferred IgG that crosses the placenta during the third trimester, meaning premature infants have significantly lower protective antibody levels), and immature T-cell function with a predominance of naive T-cells over memory T-cells. Neonatal sepsis is classified by timing of onset. Early-onset sepsis (EOS) occurs within the first 72 hours of life (some definitions extend to 7 days) and is typically caused by organisms acquired from the maternal genital tract during labor and delivery. Group B Streptococcus (GBS, Streptococcus agalactiae) is the most common cause of early-onset sepsis in term infants, followed by Escherichia coli (the leading cause in preterm and very low...