Coagulase-Negative Staph in a Tunneled Catheter

Differential time to positivity (DTP) DTP = peripheral time − catheter time = 21 − 12 = 9 hours, well above the 2-hour threshold used to support a catheter as the source. A catheter-drawn culture that turns positive at least 2 hours before a simultaneously drawn peripheral culture reflects a higher organism burden at the catheter tip.

Additional supporting evidence

• Growth in both line bottles, not one - contamination usually appears in a single bottle of a single set.
• Identical oxacillin-resistant phenotypes in the two sets, which makes two independent skin-flora contaminants less likely.
• A tunneled catheter in place for 14 months, with fever, rigors, and hypotension and no other source.
• Coagulase-negative staphylococci are the most common blood culture contaminants, so the burden of proof is higher than for S. aureus - but the DTP plus concordant phenotypes plus bilateral growth meet it.

Conclusion: probable catheter-related bloodstream infection. A single positive bottle from a single set in a stable patient would have been called a probable contaminant; this is not that scenario.

Next steps

1. Draw at least one more peripheral set before or immediately after starting antibiotics; do not delay empiric vancomycin for oxacillin-resistant coagulase-negative staphylococci in a hypotensive patient.
2. For a tunneled catheter with hypotension and a coagulase-negative staphylococcal CRBSI, catheter removal is generally recommended, particularly if the patient is unstable, the infection recurs, or the line has been in place long term. Salvage with antibiotic lock therapy is a consideration only in a stable patient with a line that cannot be replaced.
3. Examine the exit site and tunnel for erythema or drainage, and image if tunnel infection or thrombosis is suspected.
4. Repeat cultures after 48–72 hours to document clearance; persistent positivity suggests an uncontrolled source (e.g., infected thrombus or retained hardware).

If the catheter set had flagged at 26 hours (i.e., after the peripheral set at 21 hours), DTP would be negative, and the line would no longer be favored as the source. In that setting the same organism in both sets would suggest either a non-catheter source with skin-flora contamination or line colonization without line infection, and the decision about removal would hinge on clinical course and repeat cultures.

The negative repeat does not rule out bacteremia.

• Sensitivity of a single adult blood culture set is roughly 70–80%; two to three sets are needed to approach 95% or better. A single negative set meaningfully lowers but does not eliminate the probability of bacteremia.
• Here bacteremia is already documented: two sets grew the organism, so the question is not whether bacteremia exists but whether it is clearing.

Why the negative repeat is still useful It is a clearance signal. With a catheter source and appropriate therapy, cultures should sterilize within about 48–72 hours. A negative set at 6 hours is too early to be reassuring and too early to stop therapy.

Do not stop antibiotics on this basis.

• Coagulase-negative staphylococcal CRBSI in a catheter-dependent patient carries a real risk of recurrence and endocarditis, especially with prosthetic material or persistent fever.
• The duration should be guided by clinical response, repeat cultures at 48–72 hours, whether the catheter is removed, and whether complications (endocarditis, septic thrombophlebitis) are found.
• If fever and hypotension persist despite vancomycin with an oxacillin-resistant organism, consider whether the source is a septic thrombus or whether the catheter must come out.