Streptococcal Disease, Group B - Group B, Strep

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

Indications for Testing

  • Nonpregnant – infection suspicious for GBS
  • Pregnant – at risk; GBS status unknown at time of delivery

Laboratory Testing

  • Routine culture – identify GBS in blood, CSF, tissues, wounds, urine, and other body sites
  • Antenatal screening
    • Culture, PCR, 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 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 manifestation
    • Meningitis is often associated with impaired psychomotor development
  • Adult infection (95% are pregnancy-related) 


  • Intrapartum antibiotic therapy reduces attack rate in mother and neonate


Indications for Laboratory Testing

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

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

Protein, Total, CSF 0020514
Method: Reflectance Spectrophotometry

Glucose, CSF 0020515
Method: Enzymatic

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

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


Low rate of colonization gives false-negative results

Follow Up

If negative and high suspicion for GBS, perform culture

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


Anaerobe culture is NOT included with this order

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


Anaerobe culture is NOT included with this order

Additional Tests Available

C-Reactive Protein, Neonatal 0050181
Method: Immunoassay


May be helpful in evaluation of neonatal sepsis; cannot be used for infants of very low birth weight

6- and 12-hour samples required

Procalcitonin 0020763
Method: Immunofluorescence


Evaluate late-onset sepsis


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 [Accessed: Nov 2015]

General References

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

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

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

Randis T, Polin R. 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 J, Schrag S. Group B streptococcal disease in infants: progress in prevention and continued challenges. Clin Perinatol. 2010; 37(2): 375-92. PubMed

Winn H. 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: January 2016