Late-Onset Sepsis: Epidemiology, Microbiology, and Controversies in Practice.

Late-onset sepsis (LOS) is a common cause of neonatal morbidity and mortality. Causative pathogens vary by gestational age and geographic location. Preterm neonates in low-resource settings are at greatest risk and the majority of cases are due to gram-negative pathogens, especially Escherichia coli and Klebsiella species. Neonates in high-resource settings are more frequently infected with gram-positive organisms such as coagulase-negative Staphylococci and Staphylococcus aureus. Viruses, fungi, and parasites can also cause LOS and should be considered if bacterial cultures are sterile.