What are the diagnostic criteria for catheter-related bloodstream infection (CRBSI) and the recommended management?

Diagnostic Criteria for Catheter-Related Bloodstream Infection (CRBSI)

A definitive diagnosis of CRBSI requires that the same organism grows from at least one peripheral blood culture and either a catheter tip culture (≥15 CFU by semiquantitative roll-plate or ≥100 CFU by quantitative sonication), or that paired blood cultures meet specific quantitative thresholds: either a ≥3-fold higher colony count from the catheter hub compared to peripheral vein, or differential time to positivity (DTP) of ≥2 hours earlier growth from the catheter. 1, 2

Blood Culture Collection Technique

Before initiating any antimicrobial therapy, obtain paired blood samples simultaneously—one from the catheter hub and one from a peripheral vein—and clearly label each bottle to indicate the source. 1, 2, 3

Critical technical steps:

• Meticulously clean the catheter hub with alcohol, alcoholic chlorhexidine (>0.5%), or tincture of iodine, allowing approximately 30 seconds for complete drying before drawing cultures. 1, 2, 3 Skipping this drying time dramatically increases false-positive results. 2

• For peripheral blood samples, use the same antiseptic preparation with adequate skin contact and drying times. 1

• If peripheral access is impossible, draw blood cultures from at least 2 different catheter lumens, though evidence supporting this practice is limited. 1, 2 The guidelines explicitly state it is unclear whether all lumens should be cultured in such circumstances. 1, 2

Quantitative Diagnostic Methods (Without Catheter Removal)

Quantitative blood cultures:

A colony count from the catheter hub that is ≥3-fold greater than the colony count from peripheral vein blood definitively establishes CRBSI. 1, 2, 3

Differential time to positivity (DTP):

Growth of microbes from catheter-drawn blood at least 2 hours before growth is detected in peripheral blood confirms CRBSI. 1, 2, 3

Important caveat: Recent research demonstrates that DTP may fail to diagnose CRBSI caused by Candida species and Staphylococcus aureus because their biofilms disperse rapidly (within 3 hours or less), equalizing microbial loads between catheter and peripheral blood before the 2-hour threshold is reached. 4 DTP may also be unreliable for E. coli infections. 4

Catheter Tip Culture Methods (With Catheter Removal)

Short-term catheters (<14 days):

Use the semiquantitative roll-plate technique; growth of >15 CFU from a 5-cm catheter segment indicates catheter colonization. 1, 2

Long-term catheters (≥14 days):

Quantitative methods (e.g., sonication) are more sensitive because intraluminal colonization predominates; growth of >100 CFU confirms colonization. 1, 2

Subcutaneous ports:

Culture both the port reservoir contents and the catheter tip, as the reservoir provides higher diagnostic sensitivity than tip culture alone. 1, 2, 3

Pulmonary artery catheters:

Culture the introducer tip rather than the catheter itself for higher diagnostic yield. 1, 2

Antimicrobial-coated catheters:

Add specific inhibitors to culture media to prevent false-negative results. 1, 2

Clinical Findings and Interpretation

Fever is highly sensitive but poorly specific for CRBSI. 1, 2 Purulence or inflammation at the insertion site has higher specificity but low sensitivity. 1, 2

Blood cultures positive for S. aureus, coagulase-negative staphylococci, or Candida species without another identifiable source should strongly raise suspicion for CRBSI. 1, 2

When purulent drainage is present at the catheter exit site, swab the drainage for culture and Gram staining. 1

For long-term catheters, growth of <15 CFU/plate of the same organism from both the insertion site and catheter hub cultures strongly suggests the catheter is NOT the infection source. 1, 2

Management Recommendations

Empirical antimicrobial therapy:

Start empirical antibiotics immediately after obtaining blood cultures when CRBSI is suspected. 1, 2, 3

• Use vancomycin for gram-positive coverage in healthcare settings with elevated MRSA prevalence. 1, 2, 3 For institutions where MRSA isolates have vancomycin MIC values >2 μg/mL, use alternative agents such as daptomycin. 1

• Do not use linezolid for empirical therapy in patients suspected but not proven to have bacteremia. 1

• Include gram-negative coverage based on local susceptibility patterns using a fourth-generation cephalosporin, carbapenem, or β-lactam/β-lactamase inhibitor combination. 1, 2, 3

• For femoral catheters in critically ill patients, add empirical coverage for Candida species. 1

Catheter removal decisions:

Remove short-term catheters immediately if there is:

• Purulence or erythema at the insertion site 2, 3
• Unexplained sepsis or hemodynamic instability 2, 3
• CRBSI due to S. aureus, gram-negative bacilli, enterococci, fungi, or mycobacteria 2, 3

Remove long-term catheters if there is:

• Severe sepsis or hemodynamic instability 2, 3
• Suppurative thrombophlebitis or endocarditis 2, 3
• Tunnel infection or port abscess 2, 3
• Persistent bacteremia/fungemia >72 hours despite appropriate therapy 2, 3

Duration of antimicrobial therapy:

Day 1 of therapy is defined as the first day on which negative blood culture results are obtained. 1, 2, 3

Organism-specific treatment durations after catheter removal: 3

• Coagulase-negative staphylococci: 5-7 days for uncomplicated infection; 10-14 days standard; 4-6 weeks if complicated (endocarditis, osteomyelitis)
• S. aureus: 14 days minimum for uncomplicated infection; 4-6 weeks if complicated or persistent bacteremia >72 hours
• Enterococcus: 7-14 days
• Gram-negative bacilli: 7-14 days
• Candida species: 14 days after first negative blood culture

Obtain additional blood cultures if fever persists >72 hours on appropriate therapy, and remove the catheter if blood cultures remain positive 72 hours after initiating appropriate antibiotics. 3

Common Pitfalls to Avoid

• Never omit hub disinfection or shorten the drying time—this dramatically raises contamination rates and yields false-positive cultures. 2

• Do not use qualitative broth cultures of catheter tips; they lack specificity and are not recommended. 1, 2, 3

• Do not routinely culture catheter tips upon removal unless CRBSI is specifically suspected. 1, 2

• Do not routinely obtain "test of cure" blood cultures after completing therapy—there is insufficient evidence to support this practice. 1, 5

• Do not assume polymicrobial CRBSI without confirming both organisms meet diagnostic criteria, as one may represent contamination, especially coagulase-negative staphylococci. 3

• Do not delay catheter removal in short-term catheters with gram-negative bacilli or S. aureus—mortality increases significantly when treated with antibiotics alone without removal. 3