For this demonstration, we selected one disease for which we currently perform routine outpatient/ED ESSENCE surveillance (influenza) and one HAI of interest [C. difficile infection (CDI)]. First, we queried VA Inpatient ESSENCE for hospitalizations with an influenza diagnosis code (ICD-9: 487, 488). These data were compared to CDC's AHDRA hospitalizations, a voluntarily reporting system for laboratory-confirmed influenza-associated hospitalizations. Second, we queried VA Inpatient ESSENCE for hospitalizations with the CDI diagnosis code (ICD-9: 008.45) as well as total monthly discharges. Monthly rates for CDI were then calculated per 1000 total discharges. CDI rate per 100,000 population for FY 2010 was calculated using the total enrollees in VA Health Care in FY 2010 (8.343 million) as the denominator. Previous analysis from a non-VA hospital demonstrated good correlation between the CDI code and positive toxin assay (2) .