Use of a Standardized Infection Ratio (SIR) Model to Monitor a Nationwide Healthcare-Associated Clostridium difficile Prevention Initiative within the U.S. Department of Veterans Affairs (VA) Healthcare System

Background: By June of 2012 VA rolled-out a Clostridium difficile (C diff) prevention initiative to its 152 medical centers nationwide in the U.S., with a goal to reduce hospital-onset, healthcare facility-associated (HO-HCFA) cases of C diff by 30% within 2 years.  Because the recommendation for the preferred testing modality was to be molecular, there was an increase in sites using molecular diagnostics during the Initiative.  Molecular diagnostics have been noted to increase sensitivity and case ascertainment for C diff infections.

Methods: As a means to adjust for increasing molecular diagnostics, a SIR model of analysis for initiative outcomes was chosen.  The SIR model used by CDC’s National Healthcare Safety Network (NHSN) was initially evaluated, but as the VA healthcare-system is not representative of the CDC facilities participating in NHSN, adaption was needed to account for VA-specific characteristics.   The adapted model included NHSN variables of hospital size, C diff prevalence, diagnostic testing modality and affiliation with medical training customized to the VA system.  Analysis of quarterly increments of data was undertaken from July 2012 through June 2014.

Results: Using data from Oct 2010 through June 2012 as a baseline for comparison, during the two-year goal period, the raw rates of HO-HCFA declined from 9.40/10,000 Bed Days of Care in the baseline period to 8.62 in the final quarter (8.3% decrease). Using the SIR to account for use of molecular testing and other variables, the rates using a SIR model decreased by 7% (SIR =0.93) in the first quarter and continued to decrease to 16%  (SIR=0.84) by the final quarter period (p=0.02, for quarterly decline by linear regression).

Conclusion: A SIR Model can be customized to the VA healthcare system to track infections such as C diff, while accounting for some of the unique characteristics of the healthcare system.  While VA did not achieve its goal of 30% reduction, the use of a SIR model demonstrates the importance of accounting for variables which can influence rates and can help to determine additional strategies to achieve C diff prevention initiative goals.