Causes of Bacteremia
Bacteremia is primarily caused by bacterial entry into the bloodstream through various portals including the oral cavity, gastrointestinal tract, urinary tract, respiratory tract, skin, and invasive procedures, with daily activities like tooth brushing causing more frequent bacteremia than medical procedures. 1
Common Causes of Bacteremia
Microbial Pathogens
- Staphylococcus species (including S. aureus and coagulase-negative staphylococci) are leading causes of bacteremia worldwide, with S. aureus having a case fatality rate of 15-30% 2
- Streptococcus species (including S. pneumoniae, S. pyogenes, and viridans group) 1
- Enterococcus species (E. faecalis, E. faecium) are increasingly common causes of bacteremia, particularly in healthcare settings 1, 3
- Gram-negative bacilli including Escherichia coli, Klebsiella species, and Pseudomonas aeruginosa 1
- Anaerobic bacteria (Clostridium and Bacteroides species) can cause bacteremia ranging from asymptomatic to septic shock 4
Portals of Entry
Oral Cavity
- Daily oral activities cause frequent transient bacteremia:
- Poor oral hygiene leading to gingivitis and periodontitis significantly increases risk of bacteremia during these activities 5
Vascular Access Devices
- Central venous catheters, peripheral IVs, and implanted ports are common sources of bacteremia 1, 3
- Catheter-related infections most commonly involve S. aureus and coagulase-negative staphylococci 1
- Catheter removal is often necessary for persistent bacteremia, especially with certain organisms (Bacillus species, P. aeruginosa, S. maltophilia, C. jeikeium, vancomycin-resistant enterococci) 1
Urinary Tract
- Urinary tract infections, especially in the presence of obstruction or instrumentation 1
- Bacteremia rates are high following urinary tract procedures when urinary tract infection is present 1
- Enterococcal bacteremia commonly originates from urinary tract infections 6
Gastrointestinal Tract
- Gastrointestinal procedures can cause transient bacteremia:
- Esophageal dilation (up to 45%)
- Sclerotherapy (31%)
- Endoscopic retrograde cholangiopancreatography (6-18%)
- Simple endoscopy (2-5%) 1
- Intra-abdominal infections and cholangitis are significant sources of enterococcal bacteremia 6
Respiratory Tract
- Pneumonia can lead to bacteremia, though less commonly than other sources 6
- Respiratory procedures may cause transient bacteremia 1
Skin and Soft Tissue
- Skin and soft tissue infections can serve as portals of entry 1
- Surgical site infections are important sources of nosocomial bacteremia 7
Clinical Contexts
Healthcare-Associated Bacteremia
- Nosocomial bacteremia occurs in approximately 5 per 1,000 hospitalized patients annually 7
- Highest incidence occurs on the day of hospital admission and declines rapidly over the first 3-7 days 8
- Departments with highest risk include Hematology, Nephrology, Internal Medicine, Urology, and Oncology 8
- Invasive procedures, especially those involving the bloodstream, significantly increase risk 7
Community-Acquired Bacteremia
- More commonly associated with endocarditis than nosocomial bacteremia (12/35 vs 1/118 cases in one study) 6
- Often associated with pre-existing valvular heart disease 6
Special Populations
- Immunocompromised patients are at higher risk, including those with:
- Inflammatory arthropathies (rheumatoid arthritis, systemic lupus erythematosus)
- Drug-induced immunosuppression
- Radiation-induced immunosuppression 1
- Patients with prosthetic heart valves, prior infective endocarditis, or congenital heart disease with residual flow disturbances are at increased risk 1
Clinical Implications and Outcomes
- Bacteremia is associated with significant mortality:
- 22% at 30 days
- 41.4% at 1 year
- 75.8% at 10 years 8
- Risk of death remains elevated for years compared to the general population, even among 5-year survivors 8
- Polymicrobial bacteremia (especially with gram-negative bacilli) is associated with higher rates of shock and disseminated intravascular coagulation than monomicrobial bacteremia 6
Prevention Strategies
- Maintain optimal oral health through regular professional dental care and appropriate daily oral hygiene practices 1, 5
- Sterilize the urinary tract with antimicrobial therapy in patients with bacteriuria before elective procedures 1
- Implement proper infection control practices for vascular access devices 1
- Consider antibiotic prophylaxis only for specific high-risk procedures in high-risk patients (not routinely recommended for most procedures) 1