Group B Streptococcus

Peter Nguyen MSIII

Etiology

Facultative encapsulated gram-positive diplococcus

Produces a narrow zone of -hemolysis on blood agar

Most strains are bacitracin resistant Positive CAMP test

Etiology

Serologic Strains– Type Ia, Ib, Ia/c, II, III, IV, V, VI, VII, and VIII– Early onset disease can be due to any strain – Late onset disease is due to Type III in >90% of

cases

Epidemiology Colonizes ~20% of pregnant women

– Usually asymptomatic but can have UTIs, chorioamnionitis, or endometritis

40-70% of infants born to colonized mothers are colonized

Nearly 50% of sexually partners of colonized women are colonized themselves

0.2-3.7/1000 live births – Rates are diminishing with prophylaxis

0.5-2% of newborn infants born to colonized mothers

Risk Factors for Colonization Heavily colonized mothers Mothers younger than 20 African Americans Lower socioeconomic groups PROM Prolonged labor Maternal Chorioamnionitis Previous delivery with GBS disease

Early Onset v. Late Onset Occurs within the 1st

week of life (usually <72 hours)

Attack rate 1/birth weight

Accounts for 20% Cases appearing up to

6 months of age Cases after 1 month of

age occur primarily in premature and immunodeficient infants

Early Onset v. Late Onset Vertical transmission Ascending infection

(duration of ROM incidence of infection)

During passage through a colonized birth canal

Maternal transmission Nonmaternal sites:

– Nursery

– Personnel

– Community

Pathophysiology due to weakened host defense

Early Onset v. Late Onset Pneumonia with

bacteremia Pulmonary HTN

(COX) Meningitis

Bacteremia without a focus (55%)

Meningitis (35%) Osteomyelitis and

arthritis

Differential Diagnosis

HMD Amniotic fluid aspiration Sepsis from other ascending infections Metabolic and anatomic abnormalities that

manifest as sepsis

Laboratory Findings

Isolation and identification from normally sterile sites – CSF – Gastric or tracheal aspirates – Skin or mucous membranes

Laboratory Findings

Latex particle agglutination – Less sensitive than culture – Useful in patient who has had prior antibiotic

therapy, and is in sepsis without bacteremia

Laboratory Findings

Urine culture – Yields false positives due to colonization of

healthy neonates in the perineum and rectum

Urine latex test– Do not perform on an asymptomatic patient

Treatment DOC: penicillin G Empirical ABX treatment with ampicillin and an

aminoglycoside until GBS has been cultured Also susceptible to:

– Vancomycin

– Semi-synthetic penicillins

– Cefotaxime

– Ceftriaxone

– Impipnem

GBS Meningitis

Penicillin should be used in high doses (300mg/kg/day) for the treatment of GBS meningitis because of: – A high CSF inoculum – Relapse in patients treated with 200 mg/kg/day – The Relative safety of penicillin in neonates

GBS Meningitis

Obtain CSF culture within 48 hours of therapy induction

If growth is present, add an aminoglycoside to the treatment

Treatment Duration

Pneumonia: 10 days Arthritis: 2-3 weeks Osteomyelitis: 3-4 weeks Endocarditis: 3-4 weeks

Recurrent Infection

Due to persistent mucosal colonization rather than a sequestered focus

Full course of penicillin and aminoglycoside followed by rifampin

Mother’s breast milk may be a source– Culture milk – Treat mother with rifampin

Supportive Care

Hypoxia and shock DIC Seizures Increased ICP SIADH

Complications

Mortality rate ranges from 5-15% – Highest in VLBW infants, those in septic shock

or those who had a delay in therapy– Decreasing due to earlier dx and tx, increased

intrapartum prophylaxis, and ECMO

Complications Neurologic sequelae occur in 20-30% of

meningitis cases – Mental retardation – Quadriplegia/hemiplegia– Seizures – Hypothalamic dysfunction – Cortical blindness – Hydrocephalus – Bilateral deafness

Laboratory Findings Selective intrapartum chemoprophylaxis

(SIC)– IV penicillin G or ampicillin at onset of labor or

when PROM is anticipated (clindamycin for penicillin allergic patients)

– Should be implemented in communities and hospitals where GBS perinatal disease is prevalent

– Decreases the incidence of early-onset but not late-onset disease

Laboratory Findings

All infants whose mother received SIC should be observed for 48 hours for signs of infection – Neonatal infection: treatment continued for 5-7

days– Antibiotic resistance

Bibliography

Behrman, Richard E.; Kliegman, Robert; Jenson, Hal B. (1999) Nelson Textbook of Pediatrics, 16th ed Philadelphia: Saunders W.B. Co.

http://www.groupbstrep.org/