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MS WordPerinatologist Corner - C.E.U/C.M.E. Modules
Group B Streptococcal Disease in the Perinatal Period
Sponsored by The Indian Health Service Clinical Support Center
2. Background and Bacteriology
Case 2
Loretta Bahe is a 30 y/o G3P2 at 16 weeks gestation who had a first prenatal urine culture that is reported as having >100,00 colonies Streptococcus agalactiae. She has no symptoms and no known drug allergies. Is antibiotic therapy appropriate for her at this time? If so, which drug(s) would you use? Does she need intrapartum antibiotic prophylaxis as well?
Background
The group B streptococcus (GBS) has been recognized as an important
neonatal pathogen since the 1970’s.
It is associated with early onset
neonatal sepsis (EONS), as well as meningitis in infants after the first week
of life. Both types of infection have been associated with a high incidence of
both fatal outcome and neurologic damage in survivors. It is also a significant
cause of maternal morbidity in the form of endometritis, wound infections, and
bacteremia. GBS and E. coli are the two leading organisms responsible for EONS
in this country.
Bacteriology
The bacteriology
of the streptococci is interesting.
Their classification is based either
on their colony appearance on blood agar or the antigens they produce. The organisms
are classified as either alpha hemolytic (incomplete hemolysis), beta hemolytic
(complete hemolysis), or gamma hemolytic (no hemolysis). The Lancefield classification
uses antigen identification to organize the streptococci into groups A-G. Group
A streptococci, or Streptococcus pyogenes, which is beta hemolytic, is associated
with acute pharyngitis, glomerulonephritis, and acute rheumatic fever, as well
as with impetigo and necrotizing fasciitis (“the flesh-eating bacteria”).
Streptococci
was one of the first recognized obstetric pathogens, being responsible for “childbed fever” or
puerperal sepsis. The landmark clinical and laboratory work with this entity
in the mid-nineteenth century by Semmelweis and Pasteur laid the foundations
for modern microbiology as well as aseptic technique. Group B streptococci, or
Streptococcus agalactiae, so called because it is a major cause of mastitis in
dairy cattle (!), is, as noted above, the major cause of EONS, as well as maternal
perinatal infections.
There are also beta hemolytic gram-positive cocci that
are subdivided into several serotypes on the basis of their capsular polysaccharide
antigens. Groups C and F strep are mainly veterinary pathogens, and Group D strep,
the enterococcus, or Streptococcus faecalis, is well-known as an important hospital
pathogen causing severe wound and intraabdominal infections, including endometritis.
Streptococcus viridans, an important cause of endocarditis, is not Lancefield
typed, and Streptococcus pneumoniae, the pneumococcus, is of course the well-known
organism responsible
for such a large share of pulmonary infections.
