Objective: To compare silver-coated and uncoated central venous catheters regarding bacterial colonization. To assess the relative contribution of catheter hub and skin colonization to catheter tip colonization.
Design: Prospective, randomized clinical trial.
Setting: Intensive care unit in a university hospital.
Patients: Patients after cardiac surgery who required a central venous double-lumen catheter (DLC).
Interventions: Sixty-seven adult patients were prospectively randomized to receive either a silver-coated (S group, n = 34) or an uncoated control (C group, n = 33) DLC. Blood cultures were drawn at catheter removal, and removed catheters were analyzed with quantitative cultures. Typing of microorganisms included DNA fingerprinting.
Measurements and main results: Catheters were removed if no longer necessary and aseptically divided into three segments: segment A, the catheter tip; segment B, an intermediate section; and segment C, the subcutaneous portion. Bacterial catheter colonization was quantitatively measured using sonication to detach adherent bacteria from the catheter segments in the broth and subsequent culture of an aliquot. Selected isolates of coagulase-negative staphylococci and other bacteria from catheter segments were examined by means of pulsed-field gel electrophoresis (PFGE) after macrorestriction digestion of bacterial DNA to study colonization pathogenesis. Quantitatively lower bacterial colonization could be demonstrated on the silver-coated catheters (200 +/- 550 colony forming units [CFUs]/cm catheter segment; mean +/- SD). The difference in the control catheters (1120 +/- 5350 CFUs/cm catheter segment; mean +/- SD) was not, however, significant (p = .25). The frequency of colonization of at least one catheter segment was 52.9% for the silver-coated catheters and 57.6% for the control catheters (p= .44), without any significant differences in the colonization of corresponding catheter segments. The rate of significant catheter colonization (i.e., > or = 10(3) CFUs/cm catheter by quantitative catheter culture or > or = 10(3) CFUs/mL by luminal flush) was nine in the silver group and seven in the control group, a difference that failed to reach significance (p = .41). Two patients in both groups developed catheter-related bacteremia. Pattern analysis after PFGE demonstrated that about 70% of the isolates found on the catheter tip were identical with those on the skin at the insertion site, whereas about 75% were identical with those recovered from the hub. In 29% of colonized catheters, identical bacteria were found on the hub and the skin at the insertion site.
Conclusions: Silver-coating of DLCs did not significantly reduce bacterial catheter colonization compared with the control catheters. PFGE analysis of coagulase-negative staphylococci and other bacteria demonstrated various pathogenic routes of catheter-related colonization, whereby the microorganisms of the skin flora around the insertion site must be regarded as the main source of catheter-related infections.