Aggregate comorbidity scores are useful for summarizing risk and confounder control in studies of hospital-associated infections. The Chronic Disease Score -- Infectious Diseases (CDS-ID) was developed for this purpose, but it has not been validated for use in studies of Clostridium difficile Infection (CDI). Stevens, et al. (2013) sought to assess the discrimination, calibration and potential for confounder control of CDS-ID compared to age alone or individual comorbid conditions.
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Secondary analysis of a retrospective cohort study of adult inpatients withÂ two or more days of antibiotic exposure at a tertiary care facility during 2005. Logistic regression models were used to predict the development of CDI up to 60 days post-discharge. Model discrimination and calibration were assessed using the c-statistic and Hosmer-Lemeshow (HL) tests, respectively. C-statistics were compared using chi-square tests.
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CDI developed in 185 out of 7,792 patients. The CDS-ID was a better standalone predictor of CDI than age (c-statistic 0.653 vs 0.609, P=0.04). The best discrimination was observed when CDS-ID and age were both used to predict CDI (c-statistic 0.680). All models had acceptable calibration (P>0.05).
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The researchers conclude that CDS-ID is a valid tool for summarizing risk of CDI associated with comorbid conditions. Their research was published in 

Reference: Stevens V, Concannon C, van Wijngaarden E and McGregor J. Validation of the chronic disease score-infectious disease (CDS-ID) for the prediction of hospital-associated clostridium difficile infection (CDI) within a retrospective cohort. BMC Infectious Diseases 2013, 13:150 doi:10.1186/1471-2334-13-150.