Semiquantitative culture of catheter tips

Dynamics of Hemodialysis Catheter Colonization by Coagulase-Negative Staphylococci

Objectives:

Catheter colonization is a necessary but poorly characterized step in the pathogenesis of catheter-related infections. Colonization dynamics of central venous hemodialysis catheters were studied with emphasis on coagulase-negative staphylococci (CoNS) and their population genetics, antibiotic resistance, and biofilm formation. The homogeneity of CoNS colony morphotypes was evaluated.

Design:

Prospective, longitudinal study during 1,158 catheter-days with microbiological analysis of skin swabs, weekly catheter blood and brush samples, and catheter tips.

Setting:

Hemodialysis unit of a university hospital.

Patients:

Twenty-six patients with 24 non-tunneled and 5 tunneled catheters.

Results:

Nineteen (65.5%) of the catheters became colonized, 17 by CoNS. CoNS colonization of the inner lumen was observed in 17.2% of the catheters and was first detectable after 3 weeks. Colonization of the outer surface occurred in 44.8% of the catheters within a minimum of 2 weeks. PFGE of 53 CoNS revealed 10 clones and 20 unique isolates. Isolates from clones were more frequent in catheter blood and brush cultures than were unique isolates (41% vs 15%), were resistant to more antibiotics (median, 7 vs 2), and tended to more often carry theicaAgene (64.1% vs 40%). Four (23.5%) of the catheters showed colonization with a mixture of CoNS based on PFGE. The time from catheter insertion to such mixed CoNS colonization was longer than that for colonization with one CoNS PFGE pattern only (42 vs 25 days).

Conclusions:

Colonization of hemodialysis catheters is dominated by multidrug-resistant,icaA-positive CoNS clones. Mixed CoNS colonization occurs, but is delayed, suggesting a process of sequential superinfection (Infect Control Hosp Epidemiol2005;26:567-574).

Vascular catheter-related sepsis: diagnosis and prevention

Although catheter-related sepsis (CRS) is an important cause of nosocomial infection and the major complication of intravenous catheter use, there is, as yet, no consensus concerning either a useful definition of CRS or the optimal method of catheter management and prevention of infection. Semiquantitative culture of catheter tips is a useful method of diagnosis of CRS but other techniques such as quantitative catheter blood cultures and Gram staining of the catheter have roles in selected patients. The most significant impact on the prevention of CRS is made by the introduction of an intravenous therapy team. The site and method of catheter insertion, type of dressing and antisepsis, catheter flushing and use of prophylactic antibiotics are also important issues. Techniques such as guide-wire exchange and catheters such as triple lumen and total implantable venous access devices have their own infection problems. Many new and interesting approaches to the prevention of CRS are being formulated. To facilitate further progress, a standardized definition for diagnosis, and revised recommendations for prevention of CRS would be helpful.

Value of semiquantitative cultures of blood drawn through catheter hubs for estimating the risk of catheter tip colonization in cancer patients

Colonization of central catheter tips has been associated with catheter-related infections. This colonization is defined as the presence of over 15 CFU in a semiquantitative catheter tip culture performed after catheter removal. Using a simple pour-plate technique, we determined the microbial concentrations in samples of blood collected via the hubs of 205 central catheters while they were in position in 179 cancer patients. All catheters were removed within three days of blood collection via the hub and cultured semiquantitatively. We then compared the results for the hub blood cultures and catheter tip cultures. Cultures from 18% of the hub samples and 29% of the tips were positive. When a cutoff limit of 1,000 CFU/ml was used for the blood cultures, the sensitivity was 20% and the specificity was 99% for estimating catheter tip colonization. These values did not seem to be related to the underlying disease, the site of catheter insertion, or the antibiotic treatment administered at catheter removal. We conclude that, if positive, cultures of blood sampled via the catheter hub can be useful in assessing the risk of catheter colonization in cancer patients.