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Lab Manual for UCSF Clinical Laboratories

Lab Manual for SFGH

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Item Value
Available Stat? No
Test code GPB
Performed by? Microbiology (Bacteriology)
Sendout? no
Price range $
In House Availability 7 days
Principle A selective enrichment broth is used to maximize the isolation of group B strep and avoid overgrowth of other organisms. Swabs are inoculated into LIM broth [Todd Hewitt broth with colistin (10 mcg/mL) and nalidixic acid (15 mcg/mL)] and the broth is incubated for 18-24 hours. The broth is subcultured to a blood agar plate, and incubated for 48 hours. Presence or absence of group B strep is reported.
Interpretation Group B strep (Streptococcus agalactiae) cause invasive disease primarily in newborns, pregnant women, and adults with underlying medical conditions (e.g., diabetes mellitus). Detection of group B strep in the genital and gastrointestinal tracts of expectant mothers at 35 to 37 weeks gestation can identify infants at risk for infection and guide intrapartum administration of antibiotics. In infants, group B strep disease is characterized as either early-onset (i.e., occurring in infants < 7 days of age) or late-onset (i.e., occurring in infants > 7 days of age). Disease in infants usually occurs as sepsis, pneumonia, or meningitis. Other syndromes (e.g., cellulitis and osteomyelitis) can also occur.
Container type transport medium
Collection Instructions Using a swab, swab the lower vagina/introitus then the rectum (ideally though the anal sphincter) with the same or 2 different swabs without the use of a speculum. A perineum or cervical culture should not be done.
Sample type Swab
Special instructions On the Microbiology requisition, check the box for "RECTAL/VAGINAL (prenatal)" for source of specimen. Mark "Group B strep only" under the section "Test for specific organism." Do not mark routine culture/sensitivity or Gram stain. If patient reports a high risk penicillin allergy, write "PCN-Allergic" in the Patient History box on the requisition. If group B strep is recovered, the lab will test for Clindamycin and Erythromycin susceptibilities on cultures that indicate "PCN Allergic."
Stability Keep swabs in transport medium at room temperature until the next messenger pick up. Transport media will maintain group B strep viability for up to 4 days at room temperature or under refrigeration.
Additional information Since group B strep rarely cause tonsillitis or pharyngitis, screening for group B strep will not be done on throat specimens.
References 1. Murray, PR et al., Manual of Clinical Microbiology, 9th Ed., ASM Press, Washington, DC, 2007.

2. Eichenwald, EC. Perinatally transmitted neonatal bacterial infections, Infectious Disease Clinics of North America, March 1997, 11:223-239.

3. Baron, EJ et al., Cumitech 17A: Laboratory diagnosis of female genital tract infections, Amer. Soc. for Microbiol., Washington DC, 1993.

4. CDC/MMWR. Prevention of Perinatal Group B Streptococcal Disease: Revised Guidelines from CDC. August 16, 2002; 51:RR-11.
CPT coding 87081
Last Updated 8/19/2009 1:18:55 PM
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