Semiquantitative culture of subcutaneous segment for conservative diagnosis of intravascular catheter-related infection

Background: Sensitivity and negative predictive values of combined surface cultures (skin and hub) are high in the presumptive diagnosis of catheter-related infection, but specificity and PPVs are poor. The pur pose of the study was to evaluate the yield of the semiquantitative culture of the subcutaneous segment in the diagnosis of colonization of the catheter tip without removal of the catheter. Methods: A prospective study was performed in 124 nontunneled central venous catheters that were removed because of suspected infection or the end of therapy. Catheter colonization was considered if >15 colony-forming units (CFU) in the roll procedure or >1000 CFU in the quantitative Cleri procedure were recovered from the tip cultures ("gold standard"). Before removing the catheter, a semiquantitative culture of skin surrounding the point of insertion, a semiquantitative culture of the subcutaneous segment (after removing the catheter only 2 cm), a semiquantitative cultures of the hub, and a pareated quantitative blood culture were performed. Receiver operating characteristic curves were calculated to estimate the cutoff points, and a culture was considered positive when CFUs were greater than or equal to 15, greater than or equal to 15, and greater than or equal to 5 for skin, hub, and subcutaneous segment cultures, respectively. Results: Catheter colonization was detected in 51 catheters. The mean duration of catheterization was 14 +/- 8 days, and the rates of incidence of tip colonization and bacteremia were 2.9 per 100 catheter days and 1.2 per 100 catheter days, respectively. Sensitivity of skin, subcutaneous, and hub cultures analyzed individually were less than or equal to 61%; however, specificity and positive predictive values (PPVs) of subcutaneous segment cultures were significantly higher than skin cultures (94% and 88.5% vs 71.6% (p =.001) and 62% (p =.014), respectively). Sensitivity of the combined skin and hub cultures and of the combined subcutaneous segment and hub cultures were similar: 86.2% and 84.3%, respectively; however, specificity and PPVs of this latter combination were significantly higher than former: 82% and 78.1% vs 59.7% (p =.008) and 61.9% (p =.07), respectively. The likelihood ratio of a positive test for the combined subcutaneous segment and hub culture was 4.68, and only 2.13 for the combined skin and hub culture. Conclusions: These results indicate that the combined subcutaneous segment and hub culture constitutes an easy, effective procedure for the conservative diagnosis of catheter colonization.