Management of a Single Positive Blood Culture for Group B Streptococcus (GBS)
A single positive blood culture for Group B Streptococcus should be treated as a true infection rather than contamination, as GBS is considered a recognized pathogen that requires only one positive culture to be clinically significant. 1
Clinical Significance of a Single Positive GBS Blood Culture
- According to CDC guidelines, GBS is considered a recognized pathogen, not a common skin contaminant, making even a single positive culture potentially significant and meeting the criteria for a true infection 1
- Unlike common contaminants such as coagulase-negative staphylococci that require two positive cultures from separate occasions, pathogens like GBS require only one positive culture to be considered significant 1
- The presence of fever, chills, or hypotension in a patient with a single positive blood culture for GBS strongly suggests true bacteremia rather than contamination 1
Treatment Recommendations
- For non-allergic patients, penicillin G (5 million units IV initial dose, then 2.5 million units IV every 4 hours) is the first-line treatment 2
- Ampicillin (2g IV initial dose, then 1g IV every 4 hours) is an acceptable alternative for non-allergic patients 2
- For penicillin-allergic patients, clindamycin is recommended as an alternative therapy, though increasing resistance has been observed 1, 3
- Treatment should be initiated promptly as severe complications may result from delay in antibiotic treatment 4
Special Considerations
- GBS is the leading cause of neonatal meningitis and sepsis but can also cause infections in adults 4, 5
- In adults, GBS can cause various invasive infections including bacteremia, arthritis, and sacroiliitis 4
- Microbiological diagnosis frequently relies upon positive blood cultures as other specimen cultures may be negative 4
Pitfalls and Caveats
- Oral antibiotics can cause a temporary negative culture in a GBS-colonized patient, which may lead to false-negative results 6
- Relying on a negative culture for management may not be appropriate in a patient recently treated with oral antibiotics 6
- Resistance to second-line antibiotics such as erythromycin and clindamycin remains high amongst GBS, with several countries noting increased resistance rates in recent years 3
- While vancomycin remains largely effective as a last resort antibiotic, there have been documented cases of vancomycin resistance in GBS 3
For Pregnant Patients with GBS
- All pregnant women should be screened at 36 0/7-37 6/7 weeks' gestation for vaginal and rectal GBS colonization 7
- Women with GBS isolated from urine at any concentration during pregnancy should receive intrapartum antibiotic prophylaxis without need for additional screening 2
- Women who previously gave birth to an infant with invasive GBS disease should receive intrapartum prophylaxis without additional screening 2
- If GBS status is unknown at labor onset, intrapartum prophylaxis should be administered to women with risk factors: gestation <37 weeks, membrane rupture ≥18 hours, or temperature ≥100.4°F 2