Central Line-Associated Bloodstream Infection
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Direct answer
Central line-associated bloodstream infection is a bloodstream infection in a patient with a central venous catheter in place, for which no other source is identified. Coagulase-negative staphylococci are the commonest cause, with Staphylococcus aureus, Candida species and Gram-negative bacilli also important. Diagnosis combines paired blood cultures with catheter tip culture, and prevention depends on a strict insertion and maintenance bundle.
What you must remember
- Commonest organisms: coagulase-negative staphylococci, mainly Staphylococcus epidermidis, derived from skin flora at the insertion site.
- Other organisms: Staphylococcus aureus, Candida species, enterococci and Gram-negative bacilli such as Klebsiella and Pseudomonas aeruginosa.
- Source clues: skin organisms suggest insertion-site contamination, whereas Candida and Gram-negative bacilli suggest hub or infusate contamination.
- Differential time to positivity: a catheter-drawn culture turning positive about two hours before a peripheral sample supports a catheter source.
- Roll-plate tip culture: 15 or more colony forming units per catheter segment is considered significant.
- Sonication: quantitative culture of the removed tip releases organisms from the biofilm for counting.
- Insertion bundle: hand hygiene, maximal sterile barrier precautions, chlorhexidine skin antisepsis and optimal site selection.
- Dressing and review: chlorhexidine-impregnated dressings at the site, and daily review of whether each line is still needed.
A diagnostic pathway for suspected catheter infection
A fever in a patient with a central line raises the question of where the infection is. The pathway below separates a catheter source from a bloodstream infection with another origin.
- Draw paired cultures: collect one blood sample through the catheter and one peripherally at the same time, ideally before antibiotics.
- Compare the timing: record the time to positivity of each bottle, since a catheter sample turning positive about two hours earlier supports a catheter source.
- Decide on removal: remove the line if the patient is septic, the site is inflamed, or the organism is Staphylococcus aureus or Candida, as these usually need removal.
- Send the tip: after removal, send the catheter tip for roll-plate or sonication culture and interpret it by laboratory threshold.
- Choose therapy: start empirical treatment that matches the likely organisms and local resistance, and tailor it when cultures return.
- Review the need: remove any line that is no longer required, since each line-day adds risk.
A tip culture of 15 colony forming units or more, with the same organism in blood, is usually taken to confirm a catheter-related infection. Culture results should therefore be read together rather than one at a time.
Where the exam tries to catch you
Central line questions usually turn on contamination, the choice of site or the timing of cultures.
- Trap: counting one positive blood culture with coagulase-negative staphylococci as true bacteraemia Correct: a single bottle with skin flora may be contamination, so two or more sets are needed to confirm it.
- Trap: choosing the femoral site for an adult central line by default Correct: subclavian or internal jugular sites are generally preferred where feasible, with ultrasound guidance, because femoral lines are associated with higher infection rates in adults.
- Trap: expecting a tip culture from a line that is still in place Correct: the tip is available only after removal, so the culture is sent with the removed catheter.
Frequently asked questions
What is the commonest organism in central line-associated bloodstream infection?
Coagulase-negative staphylococci, mainly Staphylococcus epidermidis, are the commonest organisms in central line-associated bloodstream infection. Staphylococcus aureus, Candida species and Gram-negative bacilli cause a smaller share of cases but are often more serious.
What does the roll-plate tip culture threshold mean?
A semi-quantitative roll-plate tip culture growing 15 or more colony forming units per catheter segment is taken as significant. It supports catheter-related infection when the same organism grows from blood, and sonication is a quantitative alternative that detects biofilm organisms.
How is differential time to positivity used in central line infection?
Differential time to positivity compares the time to growth of catheter-drawn blood with that of peripherally drawn blood from the same episode. A catheter sample turning positive about two hours earlier than the peripheral sample supports a catheter source of infection.
Which insertion bundle reduces central line infection?
The insertion bundle includes hand hygiene, maximal sterile barrier precautions, chlorhexidine skin antisepsis and optimal site selection, and the maintenance bundle adds daily review of line necessity. Bundles work best when a trained observer checks each element at every insertion.
What is the difference between CLABSI and catheter-related bloodstream infection?
Central line-associated bloodstream infection is a surveillance term that counts laboratory-confirmed bloodstream infection in a patient with a central line, whatever the cause. Catheter-related bloodstream infection is a clinical diagnosis that needs evidence of a catheter source, such as matching tip and blood cultures.