Efficacy of the Gram Stain and a Rapid ELISA Test in Screening for Group B Streptococcus

Abstract

The Gram stain and a rapid enzyme linked immunosorbent assay (ELISA) test (Quidel Group B Strep Test, T.M., Quidel 10165 McKellar Court, San Diego, CA) were compared with culture for the rapid detection of group B streptococcal colonization in pregnant women. A prospective study included 203 patients, 105 in the Gram stain group and 98 in the ELISA group. Cultures were obtained in both groups and the Gram stain and ELISA test compared to the cultures. Fisher's exact test was used to analyze the data. Both the Gram stain and ELISA test had high sensitivities, 92.9 and 86.9%, respectively. However, the ELISA test had a significantly higher specificity than the Gram stain, 97.3 versus 57.1% (P = 0.036). Both tests will identify group B streptococcus in a high percentage of culture positive patients, but the ELISA test has the advantage of much higher specificity, allowing for timely treatment in at risk populations while avoiding unnecessary treatment in most culture negative patients.

Key Words:

• Group B streptococcus
• Rapid ELISA test
• Gram stain
• Immediate detection
• Greater specificity