Study Sample
We identified all hospitalized children with a diagnosis code for Cystic Fibrosis in any position (International Classification of Diseases, 9th ed., clinical modification [ICD-9 &10-CM] codes 277.00, 277.09 and E84.8, E84.9). Children younger than 1 year were excluded because of uncertainty about the true morbidity of C difficile in infants. C difficile could be both a normal commensal flora and non-pathogenic in infants younger than 1 year.