Sources of Infection for Group B Streptococcus (GBS) in Blood Cultures
The most common sources of infection for a patient with one of two positive blood cultures for Group B Streptococcus (GBS) include the urinary tract, gastrointestinal tract, and intravascular devices. 1
Primary Sources of GBS Infection
- The gastrointestinal tract serves as the natural reservoir for GBS and is likely the primary source of colonization at other body sites, with approximately 10-30% of adults colonized with GBS in their GI tract. 1, 2
- Urinary tract infections are a significant source of GBS bacteremia, occurring in both pregnant (2-4%) and non-pregnant adults. 1
- GBS in urine is considered a surrogate for heavy colonization and is associated with higher risk for invasive disease. 1, 3
- Intravascular devices, including central venous catheters, can be sources of GBS bloodstream infections. 1, 4
Diagnostic Significance of a Single Positive Blood Culture
- A single positive blood culture for GBS meets the CDC definition of a laboratory-confirmed bloodstream infection when the organism is a recognized pathogen like GBS. 1
- While a single positive culture could represent contamination, GBS is typically considered a true pathogen when isolated from blood cultures. 1, 4
Risk Factors and Patient Populations
- GBS infections are increasingly recognized in adults with chronic underlying conditions, including:
- GBS can also cause infections in immunocompetent patients without debilitating conditions. 5
Potential Sites of Secondary Infection
- Bone and joint infections, particularly spondylodiscitis (vertebral infections) can result from GBS bacteremia. 5
- Meningitis can develop as a complication of GBS bacteremia, especially in older adults with comorbidities. 6
- Skin and soft tissue infections can be both sources and consequences of GBS bacteremia. 5
Clinical Approach to Identifying the Source
- Evaluate for urinary symptoms and obtain urinalysis and urine culture, as the urinary tract is a common source of GBS bacteremia. 1, 3
- Assess for gastrointestinal symptoms or conditions, as the GI tract is the natural reservoir for GBS. 1, 2
- Inspect all vascular access devices for signs of infection, as these can be sources of GBS bloodstream infections. 1, 4
- Consider less common sources such as bone/joint infections (presenting with localized pain) or meningitis (presenting with neurological symptoms). 5, 6
Treatment Considerations
- For non-pregnant adults with GBS in urine, treatment is recommended only if they are symptomatic or have underlying urinary tract abnormalities. 1, 7
- The universal treatment recommendation for any concentration of GBS in urine applies specifically to pregnant women and should not be applied to non-pregnant patients. 7
- Initial antimicrobial therapy should be based on local epidemiology and patient-specific factors, with appropriate dosing considering potential pharmacokinetic alterations in critically ill patients. 4