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Tool helps predict C. difficile's risk of recurrence.

Many patients with Clostridium difficile infection experience repeated bouts of the illness, and a rule has been developed to accurately predict a patient's risk of recurrence.

The prediction rule, which is simple to use, takes into account a patient's age, use of antibiotics, and severity of disease. The investigators demonstrated that the rule has a diagnostic accuracy of 72%.

These factors had been shown previously to be significant independent predictors of recurrent C. difficile diarrhea, wrote Dr. Mary Y. Hu of Harvard Medical School, Boston, and her colleagues. A fourth independent predictor--the serum level of antitoxin A IgG--appeared to reduce the accuracy of the rule.

The investigators derived the Me from a study of 63 patients hospitalized with C. difficile infection between January and May 1998. They validated the tool with data collected prospectively from 64 patients hospitalized between December 2004 and May 2006.

The rule assigns 1 point to each of the following characteristics: age greater than 65 years, disease judged to be severe or fulminant in intensity, and additional antibiotic use after the discontinuation of therapy for C. difficile infection. In the validation group, recurrence occurred in 7 of 19 patients scoring 2 points or higher (37%) but in 6 of 45 patients scoring 0 or 1 (13%).

In the validation cohort, the sensitivity of the rule was 54%, the specificity was 77%, the positive predictive value was 37%, and the negative predictive value was 87%. The diagnostic accuracy was 72%. This compared favorably to the original derivation cohort, in which the rule's diagnostic accuracy was 77%.

If the rule's threshold for assigning patients to the high-risk group was changed to a score of 1 or higher, the sensitivity increased to 100% in the validation cohort, but the specificity decreased to 18%. "This alternative application may be useful in circumstances where high sensitivity is paramount," they wrote.

They also tested a combined rule that assigned an additional 2 points to a serum antitoxin A IgG level less than 1.29 ELISA units. With a threshold of 4 points or above, this combined rule appeared promising among the derivation cohort. Of these patients, 16 had antitoxin A IgG data available. Of those, all eight patients in the high-risk group had recurrent C. difficile infection, while only one of the eight patients in the low-risk group had recurrence. In this analysis, the sensitivity of the rule was 89%, the specificity was 100%, the positive predictive value was 100%, and the negative predictive value was 87.5%. The diagnostic accuracy was 94%.

Unfortunately, this rule proved to be far less predictive in the validation cohort, in which 26 patients had antitoxin A IgG data available. Infection recurred in 3 of 6 patients in the high-risk group and 5 of 20 patients in the low-risk group. This translates to a sensitivity of 38%, a specificity of 83%, a positive predictive value of 50%, and a negative predictive value of 75%. The diagnostic accuracy was 69%.


The three-factor prediction rule for recurrence was "simple, reliable, and accurate," according to the investigators. "This rule is valuable in clinical practice as it defines a high-risk population in whom awareness of the risk can facilitate more prompt recognition, diagnosis, and treatment of recurrent [C. difficile infection]. These patients are also most likely to benefit from interventions to prevent recurrence, such as infection control precautions, prudent use of antibiotics, prolongation of metronidazole or vancomycin therapy, and use of probiotics or other prophylactic measures."

The study was supported by grants from the National Institutes of Health and the Irish Health Research Board. One of the investigators, Dr. Ciaran P. Kelly of Harvard Medical School, acknowledged acting as a scientific consultant for Acambis, Actelion, BioHelix, Genzyme, Replidyne, Salix, and ViroPharm, and receiving research grant funding from Actelion, Genzyme, Massachusetts Biologics Laboratories, Medarex, and Salix Pharmaceuticals, companies that are producing or developing treatments for C. difficile infection.
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Author:Finn, Robert
Publication:Family Practice News
Geographic Code:1USA
Date:Apr 1, 2009
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