Early-onset neonatal sepsis is most commonly caused by which organism?

• A. Streptococcus agalactiae
• B. Listeria monocytogenes
• C. Escherichia coli
• D. Staphylococcus aureus

Answer: (A)

Early-onset neonatal sepsis is most often due to bacteria that the baby acquires from the mother’s birth canal during delivery. The organism most commonly responsible is Streptococcus agalactiae, known as group B Streptococcus. Many pregnant women carry this organism in the vaginal or rectal area, and transmission to the newborn during labor can lead to sepsis, pneumonia, or meningitis within the first week of life. This is why routine prenatal screening and intrapartum antibiotic prophylaxis for colonized mothers have reduced the incidence of early-onset disease. While other pathogens like Listeria monocytogenes, Escherichia coli, and Staphylococcus aureus can cause neonatal infections, group B Streptococcus remains the leading cause of early-onset sepsis.