# Catheter-Related Bloodstream Infection > Catheter-related bloodstream infection for NEET-PG Medicine, covering paired cultures, time to positivity, line removal and antibiotic duration. - Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/catheter-related-bloodstream-infection - Exam / course: NEET-PG · Subject: Medicine - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-14 - Last updated: 2026-10-14 - Reference basis: Harrison's Principles of Internal Medicine; Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases - How to cite: "Catheter-Related Bloodstream Infection", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/catheter-related-bloodstream-infection ## Direct answer Catheter-related bloodstream infection is bacteraemia or fungaemia attributed to an intravascular catheter. It is diagnosed when the same organism grows from the catheter and from peripheral blood, or when the catheter culture turns positive earlier than the peripheral sample. Coagulase-negative staphylococci are the commonest cause, while Staphylococcus aureus and Candida usually demand line removal. ## What you must remember - **Paired cultures:** draw a peripheral blood set and a set from each catheter lumen, ideally at the same time and before antibiotics where stability allows. - **Differential time to positivity:** a catheter culture turning positive at least 2 hours before the peripheral culture points to a catheter source. - **Quantitative counts:** a catheter count at least 5 times the peripheral count supports the diagnosis, and a semi-quantitative catheter tip culture above 15 colony-forming units does too. - **Commonest organisms:** coagulase-negative staphylococci lead, followed by Staphylococcus aureus, Enterobacterales, Pseudomonas and Candida species. - **Line removal:** remove the catheter for S. aureus, Candida, Pseudomonas, mycobacteria, tunnel infection or septic shock. - **Retaining the line:** uncomplicated coagulase-negative staphylococcal infection may allow the catheter to be kept with systemic therapy and an antibiotic lock. - **Duration:** uncomplicated coagulase-negative infection with the catheter removed is commonly treated for about 5 to 7 days, while complicated infection needs longer courses per current guidance. ## A graded approach from suspicion to the stop date A febrile patient with a central line needs a sequence of decisions, and each step narrows the diagnosis or changes the line plan. The route below follows the order in which the decisions are normally made at the bedside. 1. **Suspect and sample:** fever or rigors in a patient with a central line prompt paired blood cultures from each lumen and a peripheral site, drawn before antibiotics where the patient is stable enough to wait. 2. **Compare the timings:** record time to positivity for each set, because a catheter set that turns positive at least 2 hours before the peripheral set strongly suggests CRBSI. 3. **Classify the infection:** tunnelled lines, Candida, S. aureus, septic shock, persistent bacteraemia and metastatic foci count as complicated, while uncomplicated coagulase-negative infection without these features is simpler. 4. **Decide on the line:** remove a short-term catheter for the complicated organisms and features above, and consider retention only for uncomplicated coagulase-negative infection in a stable patient. 5. **Replace after clearance:** place any new line at a different site once blood cultures have cleared, rather than re-siting into the same vein while bacteraemia persists. 6. **Set the duration:** count the course from the first negative blood culture or from catheter removal, and extend it for complicated disease. ## Where the exam tries to catch you Examiners test whether the student separates colonisation from bacteraemia and matches the line decision to the organism. The traps below are the most common errors in this area. - **Trap:** a positive catheter tip culture alone confirms CRBSI — **Correct:** a colonised tip is not the same as bacteraemia, so the tip needs matching peripheral growth or a differential time to positivity. - **Trap:** the catheter must always be removed, whatever the organism — **Correct:** uncomplicated coagulase-negative infection can be managed with the line retained and an antibiotic lock, while S. aureus and Candida usually need removal. - **Trap:** six weeks of antibiotics as the default for coagulase-negative infection — **Correct:** uncomplicated coagulase-negative infection with the catheter removed usually needs only about 5 to 7 days. ## Frequently asked questions ### Which organism most often causes catheter-related bloodstream infection? Coagulase-negative staphylococci are the commonest cause of catheter-related bloodstream infection, especially in patients with long-term or frequently accessed central lines. Staphylococcus aureus, Enterobacterales, Pseudomonas and Candida are less common but often more serious. ### How is catheter-related bloodstream infection diagnosed with paired cultures? Catheter-related bloodstream infection is diagnosed by growth of the same organism from the catheter and a peripheral blood culture, with the catheter set turning positive at least 2 hours earlier. A quantitative count at least 5 times higher from the catheter also supports the diagnosis. ### When must a central venous catheter be removed in catheter-related bloodstream infection? A central venous catheter must usually be removed for Staphylococcus aureus, Candida, Pseudomonas, mycobacteria, tunnel or pocket infection, and septic shock. Uncomplicated coagulase-negative staphylococcal infection may allow the catheter to be kept with systemic therapy and an antibiotic lock. ### How long should antibiotics last for uncomplicated catheter-related bloodstream infection? Uncomplicated coagulase-negative staphylococcal catheter-related bloodstream infection with the catheter removed is commonly treated for about 5 to 7 days. Complicated infection, such as Staphylococcus aureus with metastatic foci, needs longer courses, and textbooks differ on the exact duration. ### What is an antibiotic lock in catheter-related bloodstream infection? An antibiotic lock is a concentrated antibiotic solution left inside a catheter lumen between uses, to treat infection in a catheter that is retained. An antibiotic lock supplements systemic antibiotics and does not replace them in serious bloodstream infection.