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Response to “Effect of geographic region and seasonality on Clostridium difficile incidence and hospital mortality”

Published:August 28, 2015DOI:https://doi.org/10.1016/j.ajic.2015.07.031
      To the Editor:
      We appreciate the comments regarding our recently published article on the regional and seasonal variation in Clostridium difficile infection (CDI) among hospitalized patients in the United States.
      • Argamany J.R.
      • Aitken S.L.
      • Lee G.C.
      • Boyd N.K.
      • Reveles K.R.
      Regional and seasonal variation in Clostridium difficile infections among hospitalized patients in the United States, 2001-2010.
      We agree that measuring effect size is important in any study, particularly with a large sample size where small variations between groups could result in a statistically significant difference. However, effect size is calculated without accounting for the meaning of the measures used. We believe that the use of Cohen's criteria
      • Cohen J.
      Statistical power analysis for the behavioral sciences.
      without regard to clinical significance results in underestimation of the importance of our study findings.
      From a public health perspective, the regional and seasonal variations in CDI incidence and mortality identified in our study are meaningful. Based on the actual percentage difference between the regions with the lowest (West, 6.2%) and highest (Midwest, 7.3%) mortality observed in our study, patients hospitalized with CDI in the Midwest have a 17.7% higher rate of death than hospitalized patients in the West. Similarly, a patient in the Northeast (8.0 CDIs/1,000 discharges) is 63% more likely to be hospitalized with CDI than a patient in the West (4.9 CDIs/1,000 discharges). If the observed regional and seasonal rates were reduced across the United States to the lowest rates observed in our study, a total of 42,532 cases of CDI and 1,595 deaths could be avoided each year. Using conservative estimates, each case of CDI results in an additional $2,871 in costs, potentially leading to an additional economic burden of approximately $122 million annually in our study.
      • Ghantoji S.S.
      • Sail K.
      • Lairson D.R.
      • DuPont H.L.
      • Garey K.W.
      Economic healthcare costs of Clostridium difficile infection: a systematic review.
      We do not believe that these numbers can be safely ignored.
      Finally, we agree that the regional and seasonal effects differed based on the measure of interest (ie, mortality vs incidence); however, this is not an inconsistency in our findings. It is quite plausible that one region might have higher mortality among patients with CDI, whereas another might have higher CDI incidence caused by differences in population characteristics and patient care. This calls for differential application of interventions to reduce the burden of CDI (eg, enhanced recognition and treatment to prevent mortality, improved antibiotic stewardship and infection control measures to reduce incidence), but does not invalidate the results.
      In summary, we believe that focusing on statistical measurements alone risks leaving the human and economic consequences of CDI to be forgotten. The regional and seasonal variations identified in our study are not of minimal consequence. We affirm our original conclusion that the results of this study may be used to direct preventative and therapeutic resources where and when they are needed most.

      References

        • Argamany J.R.
        • Aitken S.L.
        • Lee G.C.
        • Boyd N.K.
        • Reveles K.R.
        Regional and seasonal variation in Clostridium difficile infections among hospitalized patients in the United States, 2001-2010.
        Am J Infect Control. 2015; 43: 435-440
        • Cohen J.
        Statistical power analysis for the behavioral sciences.
        2nd ed. L. Erlbaum Associates, Hillsdale, NJ1988
        • Ghantoji S.S.
        • Sail K.
        • Lairson D.R.
        • DuPont H.L.
        • Garey K.W.
        Economic healthcare costs of Clostridium difficile infection: a systematic review.
        J Hosp Infect. 2010; 74: 309-318

      Linked Article

      • Effect of geographic region and seasonality on Clostridium difficile incidence and hospital mortality
        American Journal of Infection ControlVol. 43Issue 12
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          The recent study by Argamany et al1 concluded that the incidence and hospital mortality for Clostridium difficile infection (CDI) differed between major regions of the United States and across different seasonal times of the year. However, these conclusions were not supported by the data in their study because the authors based them exclusively on statistical significance without considering the effect size of their findings. The effect sizes of region and season on CDI were very low or near zero, contradicting their conclusion, as subsequently explained.
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