Shifting Patterns of Clostridium difficile Seasonal Variations in the Past Decade Across the United States

Introduction: Seasonal variation in Clostridium difficile infection (CDI) have been reported in several studies, noting increased number of cases during winter. Several of these studies are now relatively old, have limited number of outcome measures, or did not report findings based on time series analyses. The past decade has seen significant epidemiological changes, with emergence of more virulent strains, improved detection methods and treatments. Therefore, the aim of this study is to explore current seasonal variations of CDI incidence, mortality and costs during the past decade using a national database. Methods: Retrospective cohort study using the National Inpatient Sample from 2004 to 2013. All patients with an ICD-9CM code for a principal diagnosis code of CDI were included in the study. None were excluded. The primary outcome was the monthly CDI incidence variation. Secondary outcomes were monthly variation in mortality; resource utilization, as measured by length of hospital stay (LOS); and total hospitalization charges (adjusted for inflation). Population estimates were obtained from the US Census Bureau website. Proportions and means were compared using Fisher's exact test and Student's t-test, respectively. Odds ratios and means were adjusted for confounders using multivariate regression analysis. Results: 1,021,454 patients had a principal diagnosis of CDI during the study period. Mean age was 68 years and 65% were female. For the primary outcome, CDI incidence was highest during the spring months, with a mean incidence of 27.2 new cases per 100,000 persons, compared to 25.0, 25.2, and 24.1 new cases per 100,000 persons in summer, fall and winter, respectively (linear trend p < 0.01). Monthly incidence and proportion of admissions variations are displayed in Figure 1. The inpatient mortality rate was highest during February (3.83%) and lowest during August (2.76%), (OR: 1.29, 95%CI: 1.12-1.49, p < 0.01). Total hospitalization charges ranged from $34,655 to $36,206 in August and October, respectively (p=0.19). LOS ranged from 3.6 to 6.9 days, though after adjusting for confounders it was not significant (95%CI: 0.81-1.84, p=0.34).Figure: Monthly variation in CDI incidence and mortality rates in the United States.Conclusion: CDI seasonal variation incidence in the United States has shifted from the winter months to the springtime. Although mortality rates differed numerically, these disappeared after adjusting for confounders. Total hospitalization charges and hospital length of stay did not significantly display monthly variations.