Comparison of the roll plate method to the sonication method to diagnose catheter colonization and bacteremia in patients with long-term tunnelled catheters: a randomized prospective study.

Diagnosing catheter-related bloodstream infection (CRBSI) still often involves tip culture. The conventional method is the semiquantitative roll plate method. However, the use of a quantitative sonication technique could have additional value, as it may detect endoluminal microorganisms more easily. Because endoluminal infection tends to occur in long-term central venous catheters, we compared both techniques for patients with long-term tunnelled catheters. For 313 consecutive Hickman catheter tips from 279 hematological patients, colonization detection rates were compared by performing both techniques in a random order, using conventional detection cutoffs. Additionally, for the subgroup of patients with clinical suspicion of CRBSI (n = 89), the diagnostic values of both techniques were compared. The overall tip colonization rate was 25%. For each technique, the detection rate tended to be better if that technique was performed first. The diagnostic performance for the subgroup of patients with clinical suspicion of CRBSI was limited and not different for both methods. Sensitivity and specificity were 45% and 84%, respectively, for sonication versus 35% and 90%, respectively, for the roll plate technique. The fact that 35 of 40 patients with CRBSI received antimicrobial therapy before catheter removal and tip culture, in an attempt to salvage the catheter, may partly explain this poor performance. No differences were observed when catheters were stratified according to in situ time below or above the median of 4 weeks. The sonication culture technique was not better than the roll plate method to diagnose tip colonization or CRBSI in patients with long-term tunnelled catheters.