Background: The diagnosis of catheter-related bloodstream infection (CRBSI) should demonstrate catheter colonization of the same organism as the isolate from peripheral blood cultures, by catheter tip culture or by differential time to positivity (DTP) of catheter- drawn blood cultures versus peripheral blood cultures. The purpose of this study was to compare the sonication and the roll-plate methods of catheter tip culture.

Methods: One hundred and sixty-one catheter tips from 122 patients were submitted for catheter tip culture. Distal segments of the catheter were first inoculated using a roll-plate, and then inoculated by sonication. Sonication was performed using a BactoSonic device (Bandelin GmbH, Germany). A total of 1,018 sets of blood cultures from 7 days before to 1 day after catheter removal were analyzed for isolated organisms and DTP. Cutoffs of catheter colonization were ≥15 CFU for the roll-plate method, ≥100 CFU for sonication, and ≥2 h for DTP.

Results: Twenty-four catheter tips (14.9%) showed colonization with at least one of the two methods: 21 (13.0%) with the roll-plate method and 22 (13.7%) with sonication. The positivity rates for the two methods showed no significant difference, and the concordance rate for the two methods was 96.9% (k=0.866, P＜0.001). Blood culture was positive in 56 episodes in 44 patients, and 14 episodes of CRBSI were diagnosed in 12 patients: 10 by tip culture (two by sonication only) and 8 by DTP. Of the 122 specimens that were negative according to both methods, 4 were from the episodes of CRBSI diagnosed by DTP.

Conclusion: Roll-plate and sonication methods are comparable in diagnostic sensitivity for catheter colonization. The roll-plate and sonication catheter tip culture methods and DTP are complementary for diagnosis of CRBSI. (Ann Clin Microbiol 2015;18:7-13)