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Difficulty: MediumInfection Control and Hospital-Acquired Conditions

An infection control physician is reviewing the medical record of a patient who recently developed a fever in the intensive care unit. The patient is a 62-year-old male on postoperative day 8 following an extensive bowel resection. He has been receiving total parenteral nutrition through a multi-lumen central venous catheter. Over the past 24 hours, his temperature has risen to 38.9°C (102.0°F) with a pulse of 110/min. The catheter site appears clean and intact. Suspecting a catheter-related infection, the primary team drew paired blood cultures simultaneously from the central line and a peripheral vein. Which of the following laboratory outcomes establishes the central venous catheter as the definitive source of the bacteremia?

  1. The central venous catheter culture flags positive for microbial growth at least 2 hours before the peripheral blood cultureAnswer
  2. B
    Quantitative cultures demonstrate a colony count in the peripheral blood that is threefold higher than the central venous catheter
  3. C
    The central venous catheter culture yields coagulase-negative staphylococci, while the peripheral blood culture remains sterile
  4. D
    The central venous catheter is removed, and the distal tip culture grows >15 colony-forming units, with negative simultaneous peripheral cultures
  5. E
    The peripheral blood culture flags positive for yeast 4 hours before the central venous catheter culture

Answer

The central venous catheter culture flagging positive for microbial growth at least 2 hours before the peripheral blood culture.
Differential time to positivity (DTP) is a gold-standard diagnostic method for confirming a central line-associated bloodstream infection (CLABSI). Because the infected catheter is the primary source of the bacteremia, the microbial burden is highest within the line itself. When identical volumes of blood are drawn simultaneously into automated continuous-monitoring blood culture systems, the culture drawn from the central line will flag positive for microbial growth at least 2 hours prior to the simultaneously drawn peripheral culture. This >2-hour DTP is highly sensitive and specific for confirming that the catheter is the definitive source of the systemic infection.

Step-by-Step Solution

1
Analyze the clinical scenario of new-onset fever in a patient with an indwelling central venous catheter.
The primary differential diagnosis includes a central line-associated bloodstream infection (CLABSI).
Patients receiving total parenteral nutrition via central lines are at high risk for CLABSI, necessitating specific diagnostic testing.
2
Evaluate the criteria for diagnosing a true catheter-related bloodstream infection using paired blood cultures.
Definitive diagnosis requires demonstrating that the microbial burden is significantly higher in the catheter than in the peripheral blood.
Higher microbial burden at the source of infection confirms the catheter is responsible for seeding the bloodstream.
3
Apply the concept of Differential Time to Positivity (DTP) to the culture results.
A DTP of 2 hours or more (the central line culture flagging positive before the peripheral culture) confirms the central line as the infectious source.
Because the catheter has a higher bacterial load, identical volumes of blood placed in continuous-monitoring systems will show growth from the central line faster than from the periphery.

Key Concept

Diagnosis of Central Line-Associated Bloodstream Infection (CLABSI) utilizing Differential Time to Positivity (DTP)
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Topics

Infection Control and Hospital-Acquired Conditions

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