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of claims data, the CDI incidence of 663 per 100,000 we calculated is almost identical to that reported by Lessa et al2 (628 per 100,000 elderly persons) using 2011 EIP surveillance data and laboratory tests to identify CDI. To mitigate the lack of clinical detail concerning prior antibiotic utilization, we included vari- ables for a wide range of infections and classified them by expected type and duration of antibiotic therapy.19 We also included variables for numerous acute and chronic conditions that may result in antibiotic treatment and healthcare exposure. We calculated risk of outcomes based on exposures prior to the CDI (control) index date to quantify the probability of CDI. Although we have not considered subsequent exposures in this study, variation in CDI treatment, and other conditions after the index date, we used this method because we aimed to calculate differing risks of outcomes after balancing baseline exposures between the CDI and uninfected groups. Strengths of this study include the very large population size,
including all elderly beneficiaries coded for CDI in 2011, and generalizability of results to the Medicare fee-for-service popu- lation. We included a comprehensive set of variables into the propensity score model and achieved good balance in baseline characteristics, ensuring comparable case and control patients for the matched-pairs analyses. We performed a stratified analysis of outcomes based on the propensity score; it demonstrated het- erogeneity in the impact of CDI on mortality depending on baseline CDI risk. Overall, CDI was associated with increased risk of mortality,
new LTCF, and short-term SNF transfer within 30 days and 1 year in elderly persons. The increased mortality risk associated with CDI was much greater in persons with low baseline CDI risk and progressively decreased as the baseline risk of CDI increased. The increased risk of SNF and LTCF admissions, as well as 30-day and 1-year hospitalization, demonstrates that CDI negatively impacts patients in both the short and long terms. Our findings suggest that CDI prevention strategies should not be limited to just high-risk populations; lower-risk elderly populations may have the greatest benefit. New strategies to prevent CDI focused on the elderly need to be developed to reduce mortality, mor- bidity, and decline resulting in loss of independence and institutionalization.
Acknowledgments. We thank Cherie Hill for support with the CMS data files.
Financial support. E.R.D. received support for this study from Sanofi Pas- teur. The sponsor participated in study design, interpretation of data, and final review of the manuscript. M.A.O and E.R.D had full access to all of the data in the study and final responsibility for the decision to submit for publication. Additional funding for access to data and services through the Washington University Center for Administrative Data Research was provided by the National Center for Advancing Translational Sciences of the National Insti- tutes of Health (grant no. UL1 TR002345) and the Agency for Healthcare Research and Quality (grant no. R24 HS19455).
Conflicts of interest. M.A.O. reports consulting and speaking fees from Pfizer. C.D. reports that she is an employee of Sanofi Pasteur. E.R.D. reports grant funding from Pfizer, Rebiotix, and Merck, and consulting fees from Sanofi Pasteur, Pfizer, Synthetic Biologics, Valneva, Abbott, Biofire, Rebiotix, and Merck. D.S. reports no conflicts of interest relevant to this manuscript.
Supplementary material. To view supplementary material for this article, please visit
https://doi.org/10.1017/ice.2018.280
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