Streptococcus agalactiae
Group B Strep (GBS): Neonatal Disease
Classic Case: Group B Strep
A 3 day old newborn presents with a fever, difficulty breathing, cough, nuchal rigidity, and appears quite ill. Analysis of CSF reveals gram-positive cocci that are catalase negative, and resistant to bacitracin.
Causative Agent of:
- Neonatal Sepsis, Pneumonia, Meningitis
- Newborn infants
- Most common cause of neonatal sepsis (U.S.)
- aka “Group B Strep” (GBS)
Physical Features
- Gram-positive
- Coccus
- Non-Motile
- Encapsulated: Polysaccharide (11 serotypes)
- Group B Lancefield type
- (Group B Strep: GBS)
Growth Features
- β-hemolytic
- Clear area on blood agar
- Complete hemolysis
- Catalase negative
- Bacitracin resistant
- Hydrolyses hippurate
Epidemiology
- Normal flora of GI, genitourinary tracts
- Transient normal flora of >20% of pregnant women
- (If untreated, high transmission risk to newborn)
- U.S.: > 25,000 severe GBS infections/yr
- Neonatal risk: <0.3/1000 live births
- Most common cause of neonatal sepsis
- 80% drop since ’93
- (Moms are screened)
Reservoir and Transmission
Reservoir:
- Humans
- Colonizes GI and genitourinary tracts
- >20% of pregnant women are colonized
Transmission:
- Early-onset disease:
- To neonates via birth canal
- (or post-membrane rupture but before delivery)
- Late-onset neonatal disease:
- Via person-to-infant contact
Risk Groups
- Neonates: Risk during delivery
- Newborns: Risk post-partum
S. agalactiae, digitized SEM
Gram stain, Streptococcus sp.
Types of Hemolysis
Clinical
Group B StrepSymptoms
- Neonates:
- Most Common Neonatal Cause of meningitis, pneumonia and sepsis
- Early-onset: <7 days old
- Symptoms usually seen within few hrs of birth
- Sepsis most common outcome
- Pneumonia (10%), meningitis (5%)
- Abnormal temperature/heart rate/breathing
- Mortality rate of ~5%
- Neurological sequelae frequent with survival
- Late-onset: 1 week to 3 months old
- Bacteremia, meningitis
- Lower mortality and sequelae
- Adult diseases: Less common than neonatal
- Pregnant women: UTIs, endometritis
- Immunocompromised adults:
- Bacteremia, endocarditis, pneumonia
- Skin/joint/soft tissue infections
Pathogenesis
- Polysaccharide capsule helps to avoid phagocytosis
- Neonates are unable to phagocytose bacteria
- Inflammation causes most disease symptoms
- Similar to other Streptococci
- 15-30% of isolates:
- Resistant to erythromycin or clindamycin
Diagnosis
- Culture and staining from bodily fluids (blood, CSF)
- PCR testing: Rapid (1 hour) and sensitive
- Has not yet replaced culture methods
Prevention
- Screening of expectant mothers in third trimester
- Antibiotic prophylaxis for mothers:
- = Large decrease in early-onset disease
- But no effect on late-onset disease
- (Late-onset often via other caregivers)
Treatment
- Penicillin G
- Serious illness (or allergy to penicillin)?
- Aminoglycosides or vancomycin
References
- The CDC on Streptococcus agalactiae
- Neonatal group B streptococcal disease. 2011. Clin. Micro. Infect. 17:1294.
- A Maternal Vaccine against Group B Streptococcus: Past, Present, and Future. 2013. Vaccine. 31:D13.
- Neonatal infections: group B streptococcus. 2014. BMJ Clin. Evid. 2014: 0323.
- Epidemiology of Group B Streptococcal Disease in the United States. 1998. Clin. Microbiol. Rev. 11:497.
- Prevention of Perinatal Group B Streptococcal Disease: Revised Guidelines from CDC, 2010. MMWR. 59:1.