COSMOS Study Microbiological Results: Bacterial Colonization and Infection of Long-Term Peripheral Catheters

Background: Peripheral venous catheters (PVC) have a lower risk of the infection than central venous catheters (CVC), however, their high frequency of use makes PVC a major problem. Nowadays, there is no consensus regarding the diagnosis of PVC infections and current recommendations are not only utopian but can lead to an underestimation of infection rates.

Objectives: To compare the incidence of bacterial colonization and CRI. To identify the significant bacterial colonization in CRI, as well as the main pathogens causing bacterial colonization and CRI in long-term PVC.

Material and methods: Nurse-driven, randomized controlled trial to compare closed system (COS) versus open system (MOS), where catheters were removal only by clinical-indication and were inserted and maintained in accordance with CDC guidelines, except those that apply to routine replacement recommendations. The blinded Maki’s semiquantitative culture technique was used. ClinicalTrials.gov (NCT00665886).

Results: A total of 1183 catheters (631 patients) were randomized, 584 in the COS group (54,173 catheter-hours recorded), and 599 in the MOS group (50,296). 283 PVC were cultured, i.e. 24% of the sample. The mean in-dwell time to onset of event of COS was 239.5 hours compared to 171.9 with MOS. No significant difference in cumulative incidence or incidence density rates per 1000 catheter-days for bacterial colonization, and no statistical significance were found between rates of CRI (COS, 2.2%; MOS, 2.5%). However, we observed a 22% relative risk reduction (RRR) in CRI with COS. Of the 283 cultures, 21.9% were positive, of which the 46.8% were in COS and 53.2% in MOS. There were no significant differences between microorganisms isolated, number of colonies or type of germ. Staphylococcus was responsible for 80.3% of the colonization, and 85.7% of CRI. S. epidermidis was responsible for 48.8% of colonization and 52.4% of CRI. S. aureus was isolated in two cases (9.5%), one in each group.

Discussion: As in previous studies, despite a reduction in the incidence of CRI in closed system, the difference did not reach statistical significance. Nine CRI registered in COS were caused by Gram + (100%), while in MOS 9 CRI were recorded by Gram + (75%), 2 by Gram - (16.7%) and one by Candida (8.3%). Our data seems to confirm that bacteria isolated from closed systems are less virulent and/or that these systems may offer protection against CRI.

Conclusion: International guidelines for best clinical practice should differentiate CRI from CRBSI in the management of peripheral lines-related infections. No statistical differences exist between rates of CRI. However, there is a RRR of CRI with closed systems. A total of 29% of the catheter cultured were associated with CRI (26.5% in COS, 31.3% in MOS), suggesting less virulence of the bacteria isolated in closed systems or greater protection offered by such systems. In long-term PVC, staphylococci causes 80% of colonizations, and 100% of CRI in closed systems and while only 75% in open. There were no significant differences between isolated bacteria, the number of colonies or the type of pathogen.