Streptococcal Disease, Group B - Group B, Strep

  • 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

Group B Streptococcus (GBS) is one of the major causes of severe maternal and neonatal infections and sepsis.


  • 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: Jan 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: July 2017