Group B Streptococcal Disease

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

Diagnosis

Indications for Testing

  • Nonpregnant patients
    • Infection concerning for GBS
  • Pregnant patients
    • At-risk status (refer to Risk Factors)
    • GBS status unknown at time of delivery

Laboratory Testing

  • Routine culture
    • Identify GBS in blood, cerebrospinal fluid (CSF), tissues, wounds, urine, and other sites
  • Antenatal screening
    • Culture, PCR, nucleic acid amplification test (NAAT) – broth enrichment using combined vagina/rectal swab specimen is recommended
    • Status unknown at time of delivery – assessment of risk (delivery <37 weeks, premature rupture of membranes, and fever of >38°C [100.4°F]) is recommended for determining patient management
    • Susceptibility testing should be performed in 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 born at <37 weeks gestation, or with mother positive for chorioamnionitis or with ruptured membranes ≥18 hours
      • Limited evaluation – CBC with differential and platelet count at birth

Differential Diagnosis

Screening

Screening for Streptococcus group B by PCR or culture is routinely recommended at 35-37 weeks in pregnant women.

Background

Epidemiology

  • 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

Organism

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% of cases are pregnancy related)

Prevention

Group B strep prevention guidelines (CDC, 2010)

ARUP Lab Tests

Initial test for infection

Identify bacteria in CSF

Identify bacteria in wounds

Anaerobe culture is recommended for body fluids, tissue, and deep wound/surgical cultures; refer to anaerobe culture and gram stain

Anaerobe culture is NOT included with this order

Help differentiate viral from bacterial source

Help differentiate viral from bacterial source

Identify bacteria in normally sterile body fluids

May assist in differentiating gout from septic arthritis

Anaerobe culture is recommended for body fluids, tissue, and deep wound/surgical cultures; refer to anaerobe culture and gram stain

For CSF specimens, order CSF culture and gram stain

For blood specimens, order blood culture or blood culture, AFB and fungal

Anaerobe culture is NOT included with this order

Determine genital and rectal GBS in pregnant women

Related Tests

Use to rapidly detect a panel of common viruses, bacteria, and fungi associated with meningitis and encephalitis

Do NOT use as a replacement for CSF bacterial and/or fungal culture and Cryptococcal antigen testing for at-risk patients

A negative result does not exclude a diagnosis of meningitis or encephalitis due to infection

Panel includes Cryptococcus neoformans/gattii, cytomegalovirus (CMV), enterovirus, Escherichia coli K1, Haemophilus influenzae, herpes simplex virus 1 (HSV-1), herpes simplex virus 2 (HSV-2), human herpesvirus 6 (HHV-6), human parechovirus, Listeria monocytogenes, Neisseria meningitidis, Streptococcus agalactiae, Streptococcus pneumoniae, varicella-zoster virus (VZV)

Medical Experts

Contributor

Fisher

Mark A. Fisher, PhD, D(ABMM)
Associate Professor of Clinical Pathology, University of Utah
Medical Director, Bacteriology, Special Microbiology, and Antimicrobial Susceptibility Testing, ARUP Laboratories
Contributor

Lehman

Christopher M. Lehman, MD
Associate Professor of Clinical Pathology, University of Utah
Medical Director, University of Utah Health Hospital Clinical Laboratory, ARUP Laboratories
Contributor

Schlaberg

Robert Schlaberg, MD, MPH
Assistant Professor of Clinical Pathology, University of Utah
Medical Director, Microbial Amplified Detection, Virology, and Fecal Chemistry, and Assistant Medical Director, Virology and Molecular Infectious Disease at ARUP Laboratories

References

Additional Resources
Resources from the ARUP Institute for Clinical and Experimental Pathology®