Underlying disease severity as a major risk factor for nosocomial Clostridium difficile diarrhea.

To determine the diagnostic accuracy of an index of underlying disease severity (Horn's index) in identifying patients with a high probability of having nosocomial Clostridium difficile diarrhea as a complication of antimicrobial therapy. A prospective cohort study of 252 adult patients admitted to the hospital and receiving antibiotics. Risk facctors for C. difficile diarrhea were first determined retrospectively in a different cohort of 300 hospitalized patients (primary cohort) and then prospectively in this cohort of 252 hospitalized patients receiving antibiotics (secondary cohort). At the time of hospital admission, disease was rated by clinicians as mild (1), moderate (2), severe (3), or extremely severe (4) using a modified Horn's index. Multivariable logistic regression analysis was used to determine the odds ratio (OR) for C. difficile diarrhea associated with increasing levels of disease severity. An urban teaching hospital affiliated with a medical school in Boston, Massachusetts. The incidence of nosocomial C. difficile diarrhea was 8.7% in the primary cohort and 11% in the secondary cohort In the prospective cohort study (secondary cohort), the OR for C. difficile diarrhea associated with extremely severe disease was 17.6 (95% confidence interval, 5.8 to 53.5). The sensitivity, specificity, and positive and negative predictive values of a Horn's index score of 3 or more (severe to extremely severe disease) as a predictor of nosocomial C. difficile diarrhea were 79%, 73%, 27%, and 96%, respectively. These findings provide a means of early stratification of hospitalized patients receiving antibiotics according to their risk for nosocomial C. difficile diarrhea. Patients with severe to extremely severe disease at the time of admission may benefit from careful monitoring of antibiotic prescribing and early attention to infection control issues. In the future, these "high-risk" patients may benefit from prophylaxis studies of novel agents being developed to prevent C. difficile diarrhea.