Streptococcal Disease, Group B - Group B, Strep

Group B Streptococcus (GBS) is one of the major causes of severe maternal and neonatal infections and sepsis. GBS screening by culture or PCR is used to identify the presence of GBS in vaginal/rectal area of a pregnant woman prior to delivery.

  • Diagnosis
  • Screening
  • Background
  • Lab Tests
  • References
  • Related Topics

Indications for Testing

  • Nonpregnant – infection suspicious for Group B Streptococcus (GBS)
  • Pregnant – at risk; GBS status unknown at time of delivery

Laboratory Testing

  • Routine culture
    • Identify GBS in blood, cerebrospinal fluid (CSF), tissues, wounds, urine, and other body sites
  • Antenatal screening
    • Culture, polymerase chain reaction (PCR), nucleic acid amplification test (NAAT) – broth enrichment using combined vagina/rectal swab specimen is recommended
    • Status is unknown at time of delivery – risk-based assessment (delivery <37 weeks, premature rupture of membranes, and >38°C) is recommended for determining patient management
    • Susceptibility testing should be performed on women with penicillin allergy and high risk of anaphylaxis
  • Neonatal infection (CDC, 2010)
    • Neonate with signs and symptoms of neonatal infection
      • Initial tests – CBC with differential and platelet count, glucose, proteins, CSF studies, blood culture
    • Neonate with mother (+) chorioamnionitis or <37 weeks or ruptured membranes ≥18 hours
      • Limited evaluation – CBC with differential and platelet count at birth

Differential Diagnosis

  • Screening is routinely recommended at 35-37 weeks in pregnant females
    • Streptococcus group B by polymerase chain reaction (PCR) or culture


  • Incidence
    • Neonatal – <1/1,000 live births
    • Adult (nonpregnant) – 2-5/100,000 for invasive disease
  • Transmission – vertical from mother to neonate in 75% cases
  • Ethnicity – higher rate of neonatal infections in African Americans


  • Group B streptococci (Streptococcus agalactiae) are gram-positive cocci arranged in pairs or chains

Risk Factors

  • Maternal
    • Vaginal GBS colonization
    • Preterm delivery
    • Prolonged rupture of membranes
    • Intrapartum fever
    • Previous infant with GBS infection
  • Nonpregnant

Clinical Presentation

  • Neonatal infection
    • Early onset (first week of life) – respiratory distress, apnea, bacteremia, pneumonia, septic shock, meningitis (less frequent than in late onset)
    • Late onset (1 week-3 months) – bacteremia and meningitis are the most frequent manifestations
    • Meningitis is often associated with impaired psychomotor development
  • Adult infection (95% are pregnancy related)


Tests generally appear in the order most useful for common clinical situations. Click on number for test-specific information in the ARUP Laboratory Test Directory.

CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

Cerebrospinal Fluid (CSF) Culture and Gram Stain 0060106
Method: Stain/Culture/Identification

Wound Culture and Gram Stain 0060132
Method: Stain/Culture/Identification


Anaerobe culture is NOT included with this order

Protein, Total, CSF 0020514
Method: Reflectance Spectrophotometry

Glucose, CSF 0020515
Method: Enzymatic

Body Fluid Culture and Gram Stain 0060108
Method: Stain/Culture/Identification


Anaerobe culture is NOT included with this order

Streptococcus Group B by PCR 0060705
Method: Qualitative Polymerase Chain Reaction


ACOG Committee on Practice Bulletins-Obstetrics. ACOG Practice Bulletin No. 80: premature rupture of membranes. Clinical management guidelines for obstetrician-gynecologists. Obstet Gynecol. 2007; 109(4): 1007-19. PubMed

Prevention of Perinatal Group B Streptococcal Disease. Revised Guidelines from CDC, 2010. November 19, 2010, Vol. 59, No. RR-10. Centers for Disease Control and Prevention. Atlanta, GA [Published: Nov 2010; Accessed: Sep 2017]

General References

Cagno CK, Pettit JM, Weiss BD. Prevention of perinatal group B streptococcal disease: updated CDC guideline. Am Fam Physician. 2012; 86(1): 59-65. PubMed

Edmond KM, Kortsalioudaki C, Scott S, Schrag SJ, Zaidi AK, Cousens S, Heath PT. Group B streptococcal disease in infants aged younger than 3 months: systematic review and meta-analysis. Lancet. 2012; 379(9815): 547-56. PubMed

Larsen JW, Sever JL. Group B Streptococcus and pregnancy: a review. Am J Obstet Gynecol. 2008; 198(4): 440-8; discussion 448-50. PubMed

Randis TM, Polin RA. Early-onset group B Streptococcal sepsis: new recommendations from the Centres for Disease Control and Prevention. Arch Dis Child Fetal Neonatal Ed. 2012; 97(4): F291-4. PubMed

Sass L. Group B streptococcal infections. Pediatr Rev. 2012; 33(5): 219-24; quiz 224-5. PubMed

Sendi P, Johansson L, Norrby-Teglund A. Invasive group B Streptococcal disease in non-pregnant adults : a review with emphasis on skin and soft-tissue infections. Infection. 2008; 36(2): 100-11. PubMed

Verani JR, Schrag SJ. Group B streptococcal disease in infants: progress in prevention and continued challenges. Clin Perinatol. 2010; 37(2): 375-92. PubMed

Winn HN. Group B streptococcus infection in pregnancy. Clin Perinatol. 2007; 34(3): 387-92. PubMed

References from the ARUP Institute for Clinical and Experimental Pathology®

Medical Reviewers

Last Update: November 2017