Does Oral PCN Affect OB GBS Culture Result?

Current guidelines recommend universal collection of a vaginal-rectal swab for GBS colonization at 36-37 weeks and 6 days for the identification of patients who require intrapartum IV antibiotic coverage to prevent early onset neonatal GBS infection/sepsis. Recently, we had a patient in clinic whose GBS culture at 36 weeks was negative. Good right? Well, the patient was on amoxicillin at the time for pharyngitis. Did that course of oral PCN based therapy affect the GBS culture result? Should we believe that culture or could it be a false negative, demanding rescreen after therapy completion? There is currently a GAP here in the guidance. In this episode we will cover this controversial scenario, look at the data, and provide a real-world implementable approach to this case.

1. Kim DD, Page SM, McKenna DS, Kim CM. Neonatal Group B Streptococcus Sepsis After Negative Screen in a Patient Taking Oral Antibiotics. Obstetrics and Gynecology. 2005;105(5 Pt 2):1259-61. doi:10.1097/01.AOG.0000159040.51773.bf.

2. ACOG CO Number 797 (Replaces Committee Opinion No. 782, June 2019.); 2020

3. Mackay G, House MD, Bloch E, Wolfberg AJ. A GBS culture collected shortly after GBS prophylaxis may be inaccurate. J Matern Fetal Neonatal Med. 2012 Jun;25(6):736-8. doi: 10.3109/14767058.2011.596961. Epub 2011 Aug 1. PMID: 21801141.

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