Sonicated Vascular Catheter Tip Cultures:Quantitative Association With Catheter-related Sepsis and the Non-Utility of an Adjuvant Cytocentrifuge Gram Stain

Abstract

Microbial quantification of potentially infected intravenous catheters is used to determine whether the removed device may be the source of sepsis. In this study, the authors defined a clinically significant colony count using the sonication technique to implicate the catheter as the source of sepsis. The utility of a cytocentrifuge-prepared Gram's stain of sonication broth as a rapid test for the accurate diagnosis of catheter-related bacteremia and fungemia was also evaluated. Initially, 230 consecutive vascular catheter cultures were performed. In 14 patients, the blood culture was found to grow in the same organism as the catheter culture. The eight blood-culture positive patients with probable catheter-related sepsis had four catheters with 10(4)-10(5), and four with more than 10(5) CFU derived from the catheter sonication broth. Six bacteremias not catheter related showed three catheters with < 10(3), two with 10(3)-10(4), and one with > 10(5) CFU. One catheter-related bacteremia had a negative culture. A subsequent validation study on 175 catheter specimens using 1,000 CFU as a cut-off between a positive and negative test fully separated eight patients with catheter-related bacteremia from six patients with infection at a distant site. Cytospin Gram stain, studied in the initial evaluation, was positive in 17 catheters with < 10(3) CFU, 4 at 10(3)-10(4), 4 at 10(4)-10(5) and 9 with > 10(5) CFU in the sonication broth. No correlation was found between this test and catheter-related sepsis. From these results, the authors concluded that those catheters with counts below 10(3) CFU in the catheter sonication broth do not appear to have an association with catheter-related sepsis, and that a Cytospin Gram stain done with the sonication technique does not correlate with the presence of catheter sepsis.