Organism causing Early onset neonatal septicemia :
**Core Concept**
Early onset neonatal septicemia (EONS) refers to a systemic infection in newborns that occurs within the first 72 hours of life. It is primarily caused by vertical transmission of pathogens from the mother to the baby during delivery. The common culprits behind EONS are bacteria that colonize the maternal genital tract and gain entry into the neonatal circulation.
**Why the Correct Answer is Right**
Group B streptococcus (GBS) is the most common cause of EONS, responsible for approximately 50% of cases. GBS is a gram-positive coccus that colonizes the maternal genital and gastrointestinal tracts. During delivery, it can invade the neonatal circulation, leading to bacteremia, sepsis, and potentially life-threatening complications. The virulence of GBS is attributed to its ability to produce superoxide dismutase, which helps the bacteria evade the host's immune response.
**Why Each Wrong Option is Incorrect**
**Option A:** Escherichia coli is a common cause of late-onset neonatal septicemia, which occurs after 72 hours of age. While it can also cause EONS, it is not the leading cause.
**Option B:** Listeria monocytogenes is a rare cause of EONS, typically seen in immunocompromised mothers or in cases of maternal consumption of contaminated food products.
**Option C:** Staphylococcus aureus is a common cause of skin and soft tissue infections but is not typically associated with EONS.
**Clinical Pearl / High-Yield Fact**
GBS colonization in pregnant women is a significant risk factor for EONS. Screening for GBS colonization during pregnancy and administering intrapartum antibiotic prophylaxis (IAP) to colonized women can significantly reduce the incidence of EONS.
**Correct Answer: D. Group B streptococcus**