DefinitionNeonatal sepsis is a blood infection that occurs in an infant younger than 90 days old. Early-onset sepsis is seen in the first week of life. Late-onset sepsis occurs between days 8 and 89.Alternative NamesSepsis neonatorum; Neonatal septicemia; Sepsis - infantCauses, incidence, and risk factorsA number of different bacteria, including Escherichia coli (E.coli), Listeria, and certain strains of streptococcus, may cause neonatal sepsis.Early-onset neonatal sepsis most often appears within 24 hours of birth. The baby gets the infection from the mother before or during delivery. The following increases an infant's risk of early-onset sepsis:Group B streptococcus (group b strep) infection during pregnancyPreterm deliveryRupture of membranes (placenta tissue) that lasts longer than 24