Although the United States has made substantial progress in preventing perinatal Group B Streptococcus (GBS) disease since the 1990s, GBS remains the leading cause of early-onset neonatal sepsis in the country. In 1996, the Centers for Disease Control and Prevention (CDC), in collaboration with relevant professional societies, issued a set of guidelines for the prevention of perinatal GBS disease (CDC. Guidelines for the Prevention of Perinatal Group B Streptococcus Disease: Public Health MMWR 1996; 45 No. RR-7); these were updated and republished in 2002 (CDC. Prevention of Perinatal Group B Streptococcus Disease: Revised Guidelines in MMWR; 51 [No. RR-11]).
In June 2009, representatives from clinical practice and public health convened a meeting to reassess preventive strategies, based on the collection of relevant data since the publication of the 2002 guidelines. The most recent guidelines were issued in 2010 and have been endorsed by the American College of Obstetricians and Gynecologists, the Society of Midwives, the American Academy of Pediatrics, and the American Society for Microbiology.

Among them, the 2010 edition of the guidelines explicitly states that, in the absence of a formally approved GBS vaccine, universal antenatal screening and antibiotic prophylaxis remain the cornerstone of preventing early-onset GBS disease. It also provides detailed methodological recommendations regarding specimen collection and screening procedures for GBS in clinical laboratories, as follows:

I. Specimen Collection:

1. Compared with collecting only from the cervix and vagina without swabbing the rectum (through the anal sphincter), Simultaneous collection of vaginal anterior‑end and rectal specimens can significantly increase the positive rate of culture.

2. In outpatient settings, whether vaginal and rectal specimens are self-collected by the patient under appropriate guidance or collected by a trained professional, the positive detection rate for Group B Streptococcus (GBS) is comparable between the two approaches.

3. In clinical laboratories where immediate point-of-care testing is not feasible, the use of an appropriate transport medium can help maintain the viability of GBS in specimens; at room temperature, GBS strains can survive in such media for several days. However, after 1 to 4 days, the recovery rate of isolates declines markedly, particularly under elevated temperatures.

4. The accuracy of culture is highest when the specimen is collected within 24 hours and stored at 4°C.

II. Specimen Processing (GBS Colonization Detection Method)

The guideline lists the following mature methods, including:

Pure colonies obtained from secondary blood agar plate cultures are subjected to the CAMP test for presumptive identification.
Serum identification was performed using the GBS antiserum latex agglutination assay.
Chromogenic solid agar culture
Selective chromogenic culture in enrichment broth
DNA probe assay and nucleic acid amplification testing (NAAT, PCR)

Among these methods, selective chromogenic broth culture can significantly enhance the detection rate of β-hemolytic GBS. For GBS identification, the use of enrichment broth is recommended to improve detection sensitivity. If direct plating is employed instead of enrichment broth, approximately 50% of GBS carriers will yield false-negative results.

Published studies have demonstrated that, compared with the gold-standard enrichment broth culture and plating method, commercial PCR exhibits a minimum sensitivity of only 62.5% and a minimum accuracy of just 64.5%. One research report indicates that, If broth enrichment is performed prior to PCR testing, the sensitivity of PCR for GBS increases to 92.5%. However, using enrichment broth can prolong the testing time. For prenatal screening, the accuracy of the results is far more important than the turnaround time.