Trends and seasonal patterns in hospitalization rates of Clostridium Difficile in the US elderly

In the US, over 300,000 cases of Clostridium difficile associated diarrhea occur annually in hospitals or long-term care facilities and incidence has risen over the past two decades due to increased antibiotic use. It is plausible that C. difficile hospitalizations exhibit temporal patterns similar to seasonality of dominant pathogens for which antibiotics are prescribed. We hypothesize that the presence of pathogens and their pathogenicity are driven by environmental factors and therefore demonstrate seasonal patterns. All 448,914 hospitalization records for the US elderly for C. difficile were abstracted from the Centers for Medicare and Medicaid Services (CMS) MedPAR database for a 5-year period (1998-2002). Hospitalization rates due to C. difficile were increasing: 21.6, 22.8, 23.4, 26.6, and 32.3 per 10,000 elderly per year (p<0.05). Of all cases 10,256 (2.3%) exhibited co-morbid antibiotic resistance. The overall number of antibiotic co-morbid cases increased and the percentage of antibiotic co-morbid cases demonstrated an increasing trend (p<0.05) from 1.9% to 2.5% over the 5-year period. As expected, the highest rate of hospitalizations was observed in the 85+ years old individuals (76.5 per million population vs. 18.7 in 65-74 y.o., and 17.7 in 75-84 y.o.). Counts were organized into weekly time series and the highest rates of C. difficile were observed in mid-March (week 11 ± 0.23) for all age groups. These results suggest that C. difficile is associated with environmental characteristics and demonstrates clear seasonal patterns. Further analysis will explore seasonality in two cohorts, with and without antibiotic resistance.