Culture methods compared with the latex agglutination test for group B sterptococci detection during pregnancy

Abstract

Background The administration of antibiotic prophylaxis to laboring women who harbor group B streptococci (GBS) depends on the identification of carriers. Objectives We sought to evaluate the diagnostic accuracy of the culture methods and the antigen agglutination test for the detection of GBS in pregnant women using a PCR assay. Patients and methods A prospective cross-sectional study of women at 35–37 weeks of gestation and fulfilling the selection criteria. Two vaginal swabs were collected from each woman: one for microbiological examination and the other for direct blood agar culture and broth inoculation. The inoculated broth was used for subculture, antigen detection by the latex agglutination test, and an scpB gene PCR assay. Isolated GBS were tested for their antimicrobial susceptibility test. Results A total of 30 out of 96 pregnant women were subjected to this study according to their inclusion criteria. The highest positive percent of GBS colonization was 36.6% detected by the scpB gene PCR assay, which was considered our standard, 33.3% by the antigen detection test, 26.7% by the culture method from the inoculated broth, and 23.3% from the direct culture method. The antigen detection from the inoculated broth by the latex agglutination test was the most accurate test compared with the other test methods, with a sensitivity of 90.9% (95% confidence interval 80.4–100) and 100% (95% confidence interval 96.4–100) for both the specificity and the positive predictive value, and a diagnostic accuracy of 96.7%. All detected GBS were 100% sensitive to penicillin and vancomycin, with 54.5% resistant to clindamycin and 45.5% resistant to erythromycin. However, there was no significant association between the clinical data and the GBS colonization. Conclusion Routine screening of pregnant women for vaginal GBS colonization by the antigen detection method from the inoculated broth, and treatment of positive cases with the proper antimicrobial drugs to prevent a possible neonatal infection, which may be acquired during delivery, should be carried out.