Group B Streptococcus (GBS) Infections Workup

Updated: Oct 12, 2017
  • Author: Christian J Woods, MD, FCCP; Chief Editor: Michael Stuart Bronze, MD  more...
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Laboratory Studies

Gram stain of an appropriate specimen is a useful first test. It can show early streptococcal infection.

Isolation of group B streptococci from blood, cerebrospinal fluid (CSF), and/or a site of local suppuration is the only method for diagnosing invasive group B streptococcal infection.

Group B streptococcal antigen may be detected in blood, CSF, and/or urine and may aid in diagnosis in certain circumstances.


Imaging Studies

Consider pneumonia in the elderly bedridden patient with fever and other appropriate symptoms and neurologic deficits. Radiographs may show infiltrate or effusion in such patients.

Consider meningitis in the neurosurgical patient with fever and other appropriate symptoms. CT scanning of the head may reveal an abscess or contiguous infection. Exclude increased intracranial pressure so lumbar puncture (LP) can be performed safely.

Consider bacteremia, endocarditis, and line-related sepsis in a patient with fever. Echocardiography may reveal vegetation or evidence of valve destruction.

In a patient who is elderly, bedridden, or diabetic with fever and appropriate symptoms, consider soft-tissue infection, osteomyelitis, discitis, epidural abscess, wound infection, necrotizing fasciitis, and decubitus ulcer. Radiography of the involved area may reveal evidence of gas or bone destruction. CT scans or MRIs of the involved area may reveal phlegmon, abscess, or osteomyelitis.

In a postpartum woman or older man or woman with fever and appropriate symptoms, consider urinary tract infection and pelvic abscess. Ultrasonography of the genitourinary system or pelvis may reveal evidence of genitourinary obstruction or abscess. CT scans and MRIs may show evidence of obstruction or abscess.


Other Tests

Although rapid tests are available for assessment of maternal group B streptococcal colonization at labor, a study of two rapid tests by Daniels et al found that neither was sufficiently accurate to recommend their routine use in clinical practice. Of the two tests, polymerase chain reaction (PCR) proved significantly more accurate than optical immunoassay (OIA); nevertheless, when combined vaginal and rectal swab tests were used, PCR had a sensitivity of 84% (95% confidence index [CI], 79-88%) and a specificity of 87% (95% CI, 85-89%). The authors concluded that screening using a rapid test was not cost-effective based on its current sensitivity, specificity, and cost and that intravenous antibiotic prophylaxis directed by screening with enriched culture at 35-37 weeks' gestation is likely to be the most acceptable cost-effective strategy. [7]

Another study found that while intrapartum antibiotic prophylaxis was effective in preventing mother-to-newborn transmission of group B streptococcal colonization, prenatal cultures obtained from health care providers during routine care did not accurately predict the occurrence of infection found during labor. [8]

Schwope et al (2010) advise that, when collecting samples for group B Streptococcus screening during a pelvic examination, practitioners should collect the sample before using a bacteriostatic surgical lubricant. In a prospective cohort study in 168 patients, 20 patients tested positive for group B Streptococcus before the pelvic examination, but only 10 of those tested positive after the pelvic examination with a chlorhexidine-based surgical lubricant. [9]



Group B streptococcal pneumonia may require diagnostic and therapeutic thoracentesis if pleural effusion is present; empyema requires drainage by thoracentesis, chest tube, or surgery.

Group B streptococcal bacteremia, endocarditis, and line-related sepsis may require valve replacement because of destructive endocarditis.

Group B streptococcal soft-tissue infection, arthritis, osteomyelitis, discitis, and epidural abscess may require diagnostic aspiration and curative surgery. Necrotizing fasciitis and septic arthritis are surgical emergencies. Epidural abscess may require emergency surgery.

Group B streptococcal urinary tract infection or pelvic abscess may require aspiration with ultrasonography or CT scan guidance for a diagnostic tap to isolate the organism, to relieve obstruction, or to drain an abscess.