Predicting Clostridium difficile stool cytotoxin results in hospitalized patients with diarrhea.

OBJECTIVE

To validate a model for the prediction of Clostridium difficile cytotoxin assay results, and to identify a subgroup of patients with a very low likelihood of C. difficile-associated disease in whom the yield of routine cytotoxin testing is low.

DESIGN

Prospective cohort study. Relevant clinical symptoms, signs, and antibiotic exposure were recorded before reporting of assay results. Each predictor was assigned a score based on regression coefficients, and patients were stratified according to their total score.

SETTING

Two urban, tertiary care, university hospitals.

PATIENTS

A total of 609 consecutive adult inpatients who received testing for C. difficile cytotoxin during a 3-month period in 1994.

MEASUREMENTS AND MAIN RESULTS

The prevalence of positive cytotoxin assays was 8% in the validation set, compared with 14% in the derivation set. Defining patients without both prior antibiotic use and at least one symptom predictor (significant diarrhea or abdominal pain) as a low-risk subgroup, the misclassification rate was 2.8% (5/177) for assay results; of the five misclassified cases patients, only one was judged to have C. difficile-associated disease. Use of this rule to identify low-risk patients could have potentially averted 29% of all cytotoxin assays.

CONCLUSIONS

Patients without a history of antibiotic use and either significant diarrhea or abdominal pain are unlikely to have positive C. difficile cytotoxin assays and may not require cytotoxin testing.