Maximizing neonatal early onset group B streptococcal disease prevention with universal culture screening at 35 to 37 weeks gestation: a comparison of GBS detection rates between LIM broth and CNA culture media.

BACKGROUND AND OBJECTIVES Group B streptococcal (GBS) disease is the most common cause of early onset neonatal sepsis. The Centers for Disease Control (CDC) recommends performing recto-vaginal cultures on pregnant woman to detect GBS, followed by treatment of women with positive cultures. Our facility adopted selective culture screening in 1997 using a colistin-naladixic acid (CNA) plate media instead of the more expensive LIM broth media. CNA plate cultures cost one third that of LIM broth and allow for final results in 24 hours, versus 48-72 hours with LIM broth. We hypothesized that CNA media saves time, money, and detects GBS as effectively as LIM broth. This study determined which media is superior at detecting recto-vaginal GBS. METHODS This was a case-control study involving 152 consecutive pregnant patients at 35-37 weeks from August 1 to October 1, 2001, at Naval Hospital Bremerton, Wash. We obtained two recto-vaginal swabs from each patient. One was cultured in LIM broth and the other on CNA medium. We then compared differences in the rates of positive cultures with LIM broth versus CNA medium using chi-square statistics and calculation of odds ratios (OR). RESULTS LIM broth detected GBS in 35 of 145 (24.19%) women versus 21 of 145 (14.5%) using CNA. CNA failed to detect GBS in 15 cases in which LIM broth succeeded (OR=1.88; 95% CI=1.03-3.4). CONCLUSIONS LIM broth is superior at detecting maternal GBS colonization and is recommended over CNA plate to maximize prevention of early onset neonatal GBS disease.