Diagnostic and Therapeutic Utility of Positive Intravascular Catheter Tip Cultures.

This study evaluated the performance and clinical utility of performing intravascular catheter tip cultures (CTC). A retrospective chart review was conducted over a 2.5 year period on all patients who demonstrated growth of at least one organism on CTC. There were a total of 391 CTC performed. 88 (23%) grew at least one organism, while 303 (77%) had no growth. Of the positive CTC, 81 (92%) had blood cultures (BC) collected within 14 days, whereas 7 (8%) did not. Of the positive CTC with BC, 67 (83%) were BC-positive, whereas 14 (17%) were negative. For cases with growth on both CTC and BC, the organisms identified were concordant for 46 (69%) cases and discordant for 21 (31%). Of the concordant cases, 43 (93%) were clinically considered to be bacterial bloodstream infections that were secondary to a catheter infection. For all of the positive CTC cases total, there was no change in the antibiotics or management, with the exceptions of 2 out of 88 (2%) cases. Catheters were removed and cultured for an average of 38.6 h (range: -98 to 288 h) after positive BC results were available. Most CTC are negative, and for the CTC that are positive, most are concordant with BC results. CTC results are generally only available several days after positive BC results are known. The CTC results did not alter the antibiotic therapy or management, with the exceptions of rare cases. As such, this study concludes that CTC do not contribute diagnostic or therapeutic value. Therefore, current guidelines by the Infectious Diseases Society of America on catheter-related bloodstream infection diagnosis should be revised to exclude CTC collection. IMPORTANCE In patients with intravascular catheters who are febrile or have positive blood cultures and no other obvious sources of infection, catheter tip cultures are often obtained to evaluate potential catheter-related bloodstream infections. However, previous studies reported that the management of catheter-related bloodstream infection cases is entirely based on blood culture growth and susceptibilities and that catheter tip cultures have low diagnostic positive predictive value. Our study represents the largest contemporary evaluation that includes chart reviews on all positive catheter tip culture cases. We found that positive cultures led to no changes in antibiotics or management, except for in two cases. Furthermore, 92% of positive catheter tip cultures were associated with blood culture collections, and catheter cultures were generally available only several days after the blood culture results were known. Thus, our study supports the claim that positive catheter tip cultures add limited diagnostic and therapeutic value in suspected catheter-related bloodstream infections.

Clinical Significance of BD Bactec FX Blood Culture Incubation Beyond 96 Hours (4 Days).

Blood cultures (BC) for bacteria and yeast have traditionally been incubated for 5 days using modern instruments. Many organisms may grow sooner, and the need for the full 5-day incubation period has been questioned. This study evaluated the clinical significance of isolates recovered beyond 96 h. A retrospective chart review was conducted on all positive BC (+BC) performed via BD Bactec FX with >96 h of incubation from 5/2019 to 1/2022 at the UW Health University Hospital clinical microbiology laboratory. A total of 59,958 BC were performed; 6,031 (10%) were +BC. Of +BC, 104 (2%) demonstrated growth >96 h. The 104 cultures were from 89 patients and included 12 (12%) Staphylococcus aureus (1 MRSA), 9 (9%) yeast (8 Candida sp.), 8 (8%) Escherichia coli and 7 (7%) Enterococcus sp. (1 VRE) isolates. Fifty-six percent (n = 50) of the 89 +BC >96 h cases were clinically significant, and 26% (n = 13) resulted in antibiotic adjustments based on the +BC; 4 of these had previous positive cultures. Of the remaining 37 clinically significant +BC >96 h for which no antibiotic changes were made, 32 patients had previous positive cultures. The majority (98%) of BC bottles were positive before 96 h. For isolates that required >96 h, most (56%) were considered clinically significant, including S. aureus and E. coli cultures. Changes to antibiotic therapy were made in a minority (26%) of clinically significant cases. Based on these findings, under routine conditions, laboratories using BD Bactec FX should maintain a 120 h incubation period.