What is the interpretation of a positive placental culture?

From the Guidelines

A positive placental culture requires prompt medical attention, and treatment typically involves antibiotics based on the specific pathogen identified in the culture, with penicillin G being the first choice for Group B Streptococcus 1.

Key Considerations

• The management of a positive placental culture should prioritize the prevention of perinatal group B streptococcal disease, as outlined in the revised guidelines from the CDC 1.
• Women with GBS colonization should receive intrapartum antibiotic prophylaxis, with penicillin G being the recommended regimen for those without penicillin allergy 1.
• For women with penicillin allergy, alternative regimens such as cefazolin, clindamycin, or erythromycin may be used, depending on the susceptibility testing results 1.

Treatment Options

• Penicillin G: 5 million units IV initially, then 2.5-3 million units every 4 hours 1
• Ampicillin: 2g IV every 6 hours 1
• Clindamycin: 900mg IV every 8 hours 1
• Gentamicin: 5mg/kg IV daily 1

Important Notes

• The newborn should be monitored closely for signs of infection, as vertical transmission is possible 1.
• Maternal follow-up should include clinical assessment for postpartum endometritis or other infections 1.
• Positive placental cultures may indicate chorioamnionitis, which can lead to serious complications for both mother and baby, including preterm birth, neonatal sepsis, and postpartum infections 1.

From the Research

Positive Placental Culture Interpretation

• A positive placental culture can provide valuable information for diagnosis and management of both the mother and the fetus 2.
• The incidence of positive placental cultures is relatively low, with one study finding that only 4.6% of placentas submitted for culture had a positive result 2.
• The most common isolates from positive placental cultures are Group B streptococcus and Escherichia coli 2.
• The value of performing routine placental cultures is limited, as the current method of placental swabbing and culture technique is highly specific but not sensitive 2.

Group B Streptococcus Infection

• Group B streptococcus (GBS) is a leading cause of life-threatening neonatal bacterial infections in developed countries 3.
• GBS colonization rarely affects the newborn's health, but about 3% of colonized children develop a serious early-onset infection, particularly meningitis, which may be fatal or leave sequelae 3.
• Intrapartum antibiotic prophylaxis in women who carry GBS can reduce the risk of early-onset neonatal GBS infection from 4.7% to 0.4% (p = 0.02) 3.
• Penicillin G (benzylpenicillin) is the antibiotic of choice for GBS prophylaxis, while penicillin A (ampicillin or amoxicillin) is an alternative 3.

Prevention and Management of Perinatal GBS Infection

• The American Academy of Pediatrics and the American College of Obstetricians and Gynecologists recommend maternal intrapartum antibiotic prophylaxis based on antenatal screening for GBS colonization to prevent perinatal GBS disease 4.
• The optimal window for screening is 36 0/7 to 37 6/7 weeks of gestation, and penicillin, ampicillin, or cefazolin are recommended for prophylaxis 4.
• Pregnant women with a history of penicillin allergy are recommended to undergo skin testing to confirm or delabel the allergy 4.
• Empiric antibiotics are recommended for infants at high risk for GBS early-onset disease 4.

Antibiotic Resistance in GBS

• GBS is still recognized as being universally susceptible to beta-lactam antibiotics, but there have been reports of reduced susceptibility to beta-lactams, including penicillin, in some countries 5.
• Resistance to second-line antibiotics, such as erythromycin and clindamycin, remains high amongst GBS, with several countries noting increased resistance rates in recent years 5.
• Vancomycin is administered in instances where patients are allergic to penicillin and second-line antibiotics are ineffective, but there have been two documented cases of vancomycin resistance in GBS 5.