What is the most common cause of sepsis after chorioamnionitis?

Most Common Cause of Sepsis After Chorioamnionitis

Group B Streptococcus (GBS) is the most common cause of sepsis following chorioamnionitis, followed by Escherichia coli and other gram-negative pathogens. 1

Microbiology of Post-Chorioamnionitis Sepsis

Primary Pathogens

• Group B Streptococcus (GBS) remains the leading cause of early-onset neonatal sepsis following chorioamnionitis, particularly in term infants 1
• Escherichia coli is the second most common pathogen, especially prevalent in preterm infants and cases with maternal chorioamnionitis 1, 2
• Other gram-negative bacteria including Klebsiella species and Pseudomonas species are also significant causative organisms 1

Secondary Pathogens

• Staphylococcus aureus can cause particularly virulent chorioamnionitis and subsequent sepsis, often through hematogenous rather than ascending routes 3
• Ureaplasma species are frequently involved in chorioamnionitis but less commonly cause neonatal sepsis 4
• Polymicrobial infections occur in approximately 70% of chorioamnionitis cases 4

Clinical Implications and Management

Risk Assessment

• The risk of neonatal sepsis is significantly higher when histologic chorioamnionitis (HCA) is confirmed (RR 3.18,95% CI 2.81-5.18) 5
• Advanced fetal inflammatory response syndrome (FIRS) stage further increases sepsis risk (OR 10.35,95% CI 4.23-25.32) 5
• Despite the presence of chorioamnionitis, the rate of positive neonatal blood cultures ranges between only 0.2% and 4% 4

Antibiotic Treatment

• For infants with suspected sepsis following maternal chorioamnionitis, ampicillin plus gentamicin is the recommended first-line antibiotic regimen 1, 6
• This combination provides coverage against both GBS (ampicillin) and gram-negative organisms including E. coli (gentamicin) 6
• In cases where gram-negative sepsis is strongly suspected, cefotaxime may be added to the regimen 1

Diagnostic Approach

• All infants born to mothers with chorioamnionitis should undergo at minimum a limited evaluation including blood culture and complete blood count with differential and platelets 1
• Full diagnostic evaluation (including lumbar puncture) should be performed if the infant shows signs of sepsis 1

Special Considerations

Antibiotic Resistance

• Extended-spectrum beta-lactamase (ESBL)-producing E. coli is an emerging concern in chorioamnionitis-related sepsis 2
• Local antibiotic resistance patterns should be considered when selecting empiric therapy 1

Timing of Sepsis

• Early-onset sepsis (within first 72 hours) following chorioamnionitis is most commonly caused by GBS and E. coli 1
• Late-onset sepsis (>72 hours to 1 month) more frequently involves coagulase-negative staphylococci, particularly in developed countries 1

Prevention Strategies

• Adequate intrapartum antibiotic prophylaxis (≥4 hours of penicillin, ampicillin, or cefazolin before delivery) significantly reduces the risk of GBS sepsis in the newborn 1
• However, intrapartum antibiotics do not completely eliminate the risk of sepsis, particularly from gram-negative organisms 5

Common Pitfalls

• Relying solely on maternal GBS screening results can miss cases of sepsis, as infants can develop GBS disease despite negative maternal screening 1
• Delaying antibiotic treatment while awaiting culture results can lead to poor outcomes; treatment should begin immediately after cultures are obtained 6
• Failure to recognize that Staphylococcus aureus chorioamnionitis can occur with intact membranes and may have a more rapid disease progression and worse prognosis 3