Can microbiologists help to assess catheter involvement in candidaemic patients before removal?

Abstract

We compared the efficacy of three techniques--minimal time to positivity (MTTP) of blood cultures (BCs), differential time to positivity (DTTP) of BCs obtained from the catheter and peripheral veins and the number of positive BCs--in predicting catheter involvement in patients with well-demonstrated catheter-related candidaemia (C-RC) and non-catheter-related candidaemia (NC-RC).C-RC was defined as isolation of the same Candida species from blood and catheter tip culture (≥15 cfu/plate). A ROC curve was created for each quantitative variable to determine the best cut-off for predicting C-RC.A total of 108 episodes of candidaemia were included (84 adults and 24 children; 67 C-RC and 41 NC-RC). These were caused mainly by C. albicans (49.1%) and C. parapsilosis (30.6%). The MTTP was significantly shorter in adult patients with C-RC than in those with NC-RC (29.8 vs. 36.8 hours; p 0.035), although no cut-off value provided acceptable accuracy. DTTP had high sensitivity but low specificity for predicting CRC. However, C-RC episodes had a significantly greater number of positive BCs than NC-RC episodes. The optimal cut-off for predicting C-RC was at least two positive BCs out of three, with the following validity values: sensitivity, 100%; specificity, 62.5%; positive predictive value, 83.3%; negative predictive value, 100%; accuracy, 87.0%.None of the tests evaluated allow a clear-cut prediction of C-RC and the criteria accepted for bacteraemia should not be automatically extrapolated to candidaemia. We found that a low number of positive BCs with Candida had a high negative predictive value for a catheter origin.

Diagnostic Usefulness of Differential Time to Positivity for Catheter-Related Candidemia

“…For other Candida species, however, the sensitivity and specificity of a DTP of Ն120 min were 89% and 90%, respectively. In this study, the TTP of C. glabrata was significantly longer than those of other Candida species, consistent with the results of previous studies (10)(11)(12). Because of the longer TTP for C. glabrata, we hypothesized that the optimal DTP cutoff for C. glabrata might be longer than that of other Candida species.…”

“…Ben-Ami et al (11) reported that a TTP in the peripheral blood of Ն30 h ruled out the CVC as the source of candidemia (a TTP of Յ30 h displayed a sensitivity and specificity of 100% and 51%, respectively, for detecting definite CRC), but most patients in that study were nonneutropenic (11). The diagnostic performance of TTP among neutropenic patients may differ from that among nonneutropenic patients because of the higher proportion of C. tropicalis coming from the gastrointestinal tract in neutropenic patients (21) and the shorter TTP of C. tropicalis (10)(11)(12). Further studies with a large number of neutropenic patients should be performed to evaluate this issue.…”

“…The high sensitivity and low specificity in that study may be attributed to two factors: the small number of patients with positive simultaneous blood cultures (19 patients with CRC and 5 patients with non-CRC) and a difference in the definitions of CRC and non-CRC between that study and ours. In the study by Bouza et al (10), patients with candidemia were classified as having CRC or non-CRC according to the results of catheter tip culture alone. However, since catheter tip culture alone is not sensitive enough for diagnosing CRC, we classified the patients on the basis of clinical features, including alternative sites of candidemia and exposure to antifungal agents, in addition to the catheter tip culture results.…”

Value of Superficial Cultures for Prediction of Catheter-Related Bloodstream Infection in Long-Term Catheters: a Prospective Study

“…This, particularly, represents a big problem in the neonatal population and in patients whose catheters have persistent occlusion. Moreover, the application of DTTP evaluation for catheter-related candidemia has not been already established (34,35). Therefore, the use of a rapid and easy-to-perform technique such as superficial culture analysis may allow us to solve these problems.…”

A Statistical Approach for Determination of Disk Diffusion-Based Cutoff Values for Systematic Characterization of Wild-Type and Non-Wild-Type Bacterial Populations in Antimicrobial Susceptibility Testing

“…The ROC curve methodology was first developed in the 1950s for signal analysis and has been frequently used since than also for the assessment of the accuracy of medical imaging devices (17,18). Over the years, ROC curve analysis has also been increasingly applied for evaluation of microbiological diagnostic tests (19)(20)(21)(22). In this …”