Introduction: Catheter-related bloodstream infection (CR-BSI) due to central venous lines is estimated to occur in 80,000 intensive care unit (ICU) patients each year in the USA. While traditional epidemiological criteria require matching catheter and blood cultures, more recent criteria only require bacteremia with the absence of an identified non-catheter source. Most recent clinical practice guidelines now recommend treating Staphylococcus aureus catheter colonization in the absence of bacteremia. Clinically however, bacteremia with any known pathogen will necessitate antimicrobial therapy, regardless of catheter culture results. We therefore sought to determine the clinical utility of vascular catheter cultures in critically ill patients.

Methods: We retrospectively reviewed all positive (> 15 colony forming units [cfu] by semiquantitative roll-plate technique) vascular catheter tip cultures (CTCs) from Sept 1, 2006 through mid-November 2009 in the 40-bed, mixed medical-surgical ICU tower of a large university hospital. CR-BSI was defined by a matching positive blood culture obtained shortly before or up to 1 day after the time of catheter removal.

Results: A total of 474 CTCs were obtained. 234 (49%) were negative. 108 (23%) had < 15 cfu/roll.

Total CTCs	Positive CTCs	# CR-BSI
474	132 (28%)	48 (36%)

In 47 of 48 (98%) cases of CR-BSI, the positive blood culture occurred +/- 1 day from the catheter’s removal and dictated antibiotic therapy. In only 1 of 48 (2%) cases of CR-BSI did the catheter’s removal and culture significantly (> 1 day) precede the positive blood culture. 23% of positive CTCs had polymicrobial growth at > 15 cfu/roll. In comparison, hospital epidemiology surveillance reported 39 cases of confirmed CR-BSI in this patient cohort.

Only 5 cases (4% of all positive CTCs, 1% of all CTCs) of S. aureus catheter colonization (> 15 cfu/roll) in the absence of bacteremia were identified. 4 of these 5 patients had been started on vancomycin prior to the index colonized catheter being removed.

The microbiology laboratory costs for the 474 CTCs, organism identification and sensitivity testing were approximately $20,000 and required 205 microbiology technician hours.

Conclusion: In an ICU patient population, only about 1/4th of vascular catheters removed and cultured are positive for significant bacterial colonization. Only about 1/3rd of positive CTCs are associated with CR-BSI. 98% of all CR-BSIs can be identified by bacteremia which dictates antimicrobial therapy either prior to or coinciding with catheter removal. Therefore, since CTCs rarely change therapy, our data suggest that routine vascular catheter cultures in suspected CR-BSI in the ICU setting may not be required.