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

Anaerobe culture is NOT included with this order

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

Determine whether GBS is organism causing infection

Anaerobe culture is NOT included with this order

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