Do central lines increase the risk of developing gram-negative bacilli bacteremia?

Central Lines and Gram-Negative Bacilli Bacteremia

Central venous catheters (CVCs) do increase the risk of gram-negative bacilli bacteremia, though they are more commonly associated with gram-positive infections. Gram-negative bacteria account for approximately 20-25% of catheter-related bloodstream infections (CRBSI) in patients with central venous catheters. 1

Epidemiology and Causative Organisms

• In patients with hematologic malignancies or solid tumors, gram-positive organisms account for 60-70% of CRBSI, while gram-negative bacteria (including Escherichia coli, Pseudomonas aeruginosa, and Klebsiella species) are found in 20-25% of CRBSI cases 1
• The most common gram-negative organisms causing catheter-related infections include Escherichia coli, Pseudomonas aeruginosa, and Klebsiella species 1
• Stenotrophomonas maltophilia bacteremia is strongly associated with catheter-related infections (odds ratio 5.78) 2
• Polymicrobial bacteremia is more likely to be catheter-related (odds ratio 4.04) compared to monomicrobial infections 2

Risk Factors for Gram-Negative CRBSI

• Duration of catheterization beyond 1 week significantly increases infection risk 1
• Catheter site selection impacts risk - femoral and jugular sites have higher infection rates than subclavian sites 1, 3
• Use of central lines for parenteral nutrition increases colonization rates and subsequent infection risk 1
• High level of skin colonization at the insertion site and catheter hub/connector is a predictor for catheter-associated bloodstream infections 1
• Male gender and patients with acute myeloid leukemia have increased risk for catheter-associated bloodstream infections 1
• Subclinical thrombosis of the catheterized vein may be an important risk factor for subsequent catheter-related infection 1
• Patients with hematologic malignancies are at higher risk for catheter-related infections than patients with solid tumors 1

Pathogenesis of Gram-Negative CRBSI

• For short-term catheters (used <14 days), infections primarily occur through extraluminal migration of skin organisms at the insertion site into the cutaneous catheter tract 4, 3
• For long-term catheters (used ≥14 days), contamination of the catheter hub contributes substantially to intraluminal colonization 4, 3
• Gram-negative bacteria are typically isolated only from catheters of patients with overt infections, unlike gram-positive organisms which may be found in colonized but non-infected catheters 5
• Colonization of the CVC by microorganisms appears to be a major risk factor for subsequent catheter-related thrombosis, which further increases infection risk 1

Diagnostic Considerations

• Definitive diagnosis of catheter-related bloodstream infection requires either:
  • Growth of the same pathogen from both peripheral blood culture and catheter tip culture 1
  • Growth of the same pathogen from both catheter blood culture and peripheral blood culture with differential time to positivity ≥2 hours 1
• For gram-negative bacteremia, quantitative blood cultures showing >1000 CFUs from CVC blood cultures strongly suggests catheter-related infection (odds ratio 4.39) 2
• Neutropenia is less commonly associated with catheter-related gram-negative bacteremia (odds ratio 0.26), suggesting an alternative source of infection in these patients 2

Management Implications

• Prompt removal of the central catheter is recommended when S. maltophilia or other non-enteric gram-negative rods are isolated from blood cultures 6
• For enteric gram-negative rod bacteremia, catheter sterilization may be attempted but has a low success rate (only about 37% of catheters can be retained without complications) 6
• The presence of bloodstream infection in addition to catheter colonization does not appear to significantly alter mortality outcomes, challenging the traditional distinction between "colonization" and "infection" 7
• Follow-up blood cultures add little value in the management of gram-negative bacteremia once appropriate antibiotics have been initiated 8

Prevention Strategies

• Select the optimal insertion site (subclavian preferred over jugular or femoral) 1, 3
• Use maximal sterile barrier precautions during insertion 4
• Implement proper hand hygiene before catheter insertion and maintenance 4
• Use >0.5% chlorhexidine skin preparation with alcohol for antisepsis at the insertion site 4
• Apply sterile, transparent dressings and change them according to protocol 4
• Choose catheters with the minimum number of lumens necessary for patient management 4
• Consider antimicrobial-impregnated catheters for high-risk patients 4

Central venous catheters clearly increase the risk of gram-negative bacteremia, though at a lower rate than gram-positive infections. Prompt identification of risk factors and implementation of preventive strategies are essential to reduce morbidity and mortality associated with these infections.