Streptococcal Disease, Group B - Group B, Strep


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

Clinical Background

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
Test Name and Number Recommended Use Limitations Follow Up
Cerebrospinal Fluid (CSF) Culture and Gram Stain 0060106
Method: Stain/Culture/Identification

Identify agent of presumed meningitis

Protein, Total, CSF 0020514
Method: Reflectance Spectrophotometry

Help differentiate viral from bacterial source

Glucose, CSF 0020515
Method: Enzymatic

Help differentiate viral from bacterial source

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

Initial test for infection

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

Determine genital and rectal colonization status in adults

Screen pregnant women at 35-37 weeks

Low rate of colonization gives false-negative results

If negative and high suspicion for GBS, perform culture

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

Determine whether GBS is organism causing infection

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

Determine whether GBS is organism causing infection

Additional Tests Available
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
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