Streptococcal Disease, Group B

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

Skin/soft tissue
- Cellulitis
- Diabetic foot infection
- Wound infection
- Necrotizing fasciitis
Systemic symptoms
- Meningitis
- Sepsis (neonatal, maternal)
- Osteomyelitis
- Bacterial pneumonia
- Diskitis
- Septic arthritis
- Infective endocarditis
- Epidural abscess
Pregnancy related
- Endometritis
- Urinary tract infection, female
- Chorioamnionitis

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.

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
- Diabetes mellitus
- Cancer
- Age >65 years

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)
- Pregnancy and parturition
  - Chorioamnionitis, endometritis
- Nonpregnant
  - Soft tissue and skin infections – erysipelas, cellulitis, necrotizing fasciitis, myositis, toxic shock syndrome
  - Bone pain – osteomyelitis, septic arthritis
  - Urinary tract infections
  - Cardiovascular – endocarditis
  - Central nervous system – meningitis
  - Bacteremia

Treatment

Intrapartum antibiotic therapy reduces attack rate in mother and neonate

Tests generally appear in the order most useful for common clinical situations

Test name: CSF Bacterial Culture (Includes Gram Stain 0060101)

ARUP #: 0060106

Methodology: Standard reference procedures for bacterial stain, aerobic culture, and identification

Use:

Identify agent of presumed meningitis

Test name: Protein, Total, CSF

ARUP #: 0020514

Methodology: Reflectance Spectrophotometry

Use:

Help differentiate viral from bacterial source

Test name: Glucose, CSF

ARUP #: 0020515

Methodology: Enzymatic

Use:

Help differentiate viral from bacterial source

Test name: CBC with Platelet Count & Automated Differential

ARUP #: 0040003

Methodology: Automated Cell Count with Flow Cell Differential

Use:

Initial test for infection

Test name: Streptococcus Group B by PCR

ARUP #: 0060705

Methodology: Qualitative Polymerase Chain Reaction

Use:

Determine genital and rectal colonization status in adults

Screen pregnant women at 35-37 weeks

Limitations:

Low rate of colonization gives false-negative results

Follow-up:

If negative and high suspicion for GBS, perform culture

Test name: Body Fluid Culture (Includes Gram Stain 0060101)

ARUP #: 0060108

Methodology: Standard reference procedures for bacterial stain, aerobic culture, and identification. Anaerobe culture performed on properly collected specimens

Use:

Determine whether GBS is organism causing infection

Test name: Wound Culture (Includes Gram Stain 0060101)

ARUP #: 0060132

Methodology: Standard reference procedures for bacterial stain, aerobic culture, and identification. Anaerobe Culture is performed on properly collected specimens (Anaerobe culture 0060143).

Use:

Determine whether GBS is organism causing infection

Additional Tests Available

Test name: C-Reactive Protein, Neonatal

ARUP #: 0050181

Methodology: Immunoassay

Comments:

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

6- and 12-hour samples required

Test name: Procalcitonin

ARUP #: 0020763

Methodology: Immunofluorescent