Diagnosing Catheter-Related Bloodstream Infections

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The summary below is from the full report titled "Differential Time to Positivity: A Useful Method for Diagnosing Catheter-Related Bloodstream Infections." It is in the 6 January 2004 issue of Annals of Internal Medicine (volume 140, pages 18-25). The authors are I. Raad, H.A. Hanna, B. Alakech, I. Chatzinikolaou, M.M. Johnson, and J. Tarrand.

What is the problem and what is known about it so far?

When bacteria get into the blood, serious problems called bloodstream infections can result. The most serious bloodstream infections occur in sick, hospitalized patients or in people with complicated illnesses such as cancer or kidney failure requiring dialysis. Many of these people have tubes threaded into large veins (central venous catheters) to give medicines or fluids. The tubes sometimes become infected and cause catheter-related bloodstream infections (CRBSIs). Catheter-related bloodstream infections are often difficult to diagnose. Usually, doctors remove the catheter and culture its tip. With this approach, people without CRBSI end up having their catheters removed unnecessarily. Finding a way to diagnose CRBSI that does not rely on catheter removal would be helpful.

Why did the researchers do this particular study?

To see whether blood cultures drawn from central catheters that grow sooner than cultures drawn from peripheral veins help identify CRBSI.

Who was studied?

Patients at a cancer center whose blood cultures drawn from central catheters and from peripheral veins grew the same type of bacteria.

How was the study done?

The researchers reviewed blood culture reports between September 1999 and November 2000 from a large academic cancer center in Texas. They examined results of blood cultures drawn simultaneously from a central catheter and a peripheral vein that grew the same bacteria. The researchers recorded when cultures were drawn and when cultures became positive. They noted the difference in time between central and peripheral cultures becoming positive (differential time to positivity [DTP]).

The researchers also assessed which infections were CRBSI. Some patients had had their central catheters withdrawn and the tips of the catheter cultured. If these cultures grew large amounts of bacteria or if the blood cultures from the central catheter grew large amounts of bacteria compared with the peripheral vein cultures, the researchers called the infection CRBSI. The researchers then compared the DTP in infections that were and were not CRBSI.

What did the researchers find?

Patients with CRBSI more often had DTP of 120 minutes or more than did patients without CRBSI. When the culture drawn from the catheter became positive at least 120 minutes earlier than the peripherally drawn culture, the odds of CRBSI increased by a factor of 5.9.

What were the limitations of the study?

The study was from a single cancer center. Patterns of CRBSIs may vary in different areas. Primary care doctors decided when and in whom to draw simultaneous central and peripheral cultures and when to withdraw and culture catheters. They did not use uniform criteria to guide these decisions, and they may have missed some CRBSIs.

What are the implications of the study?

A DTP of at least 120 minutes between centrally and peripherally drawn blood cultures helps diagnose CRBSI.