In our analysis we detected a 23% annual increase in CDAD hospitalizations in the 6-year period from 2000 through 2005. Moreover, the absolute number of CDAD hospitalizations more than doubled in all age groups except the youngest, for whom they increased by 74.1% over the study period. Additionally, we estimated that the age-adjusted case-fatality rate for CDAD hospitalizations nearly doubled from 1.2% in 2000 to 2.2% in 2004.
Our numbers help put in perspective the observed increasing mortality rates related to CDAD in the United States. The recent report by Redelings et al. noted an increase from 5.7 to 23.7 deaths with CDAD per million population from 1999 through 2004 in the United States, representing a 35% adjusted per annum increase (1
). By observing a 23% per annum increase in the volume of hospitalizations with CDAD in the period 2000–2005, we demonstrate that at least half of the reported mortality increase with CDAD is due to an increase in the incidence of hospitalizations with this severe infection. Increased hospitalization may in turn be related to a simple increase in the overall volume of CDAD or reflect the increased virulence of the organism, leading to more cases of severe disease requiring hospitalization. We have also estimated that the unadjusted case-fatality rate did indeed increase from 1.2% in 2000 to 2.3% in 2004. While this doubling of deaths with CDAD is mirrored almost perfectly by the more-than doubling of CDAD admissions among all but the youngest age groups, who cumulatively represent 90% of all CDAD hospitalizations, age-adjusting the 2004 case-fatality estimate did not change it substantially. This finding indirectly confirms that the reported increase in CDAD deaths likely represents the effects of increased virulence of the organism (1
Our analysis relied on ICD-9-CM coding to identify CDAD-related hospitalizations. Studies correlating the presence of the diagnostic code for CDAD to the presence of a laboratory confirmation of the disease have not suggested a clear over- or underdiagnosis trend in the administrative coding (2
). However, the administrative nature of the data may have predisposed our case ascertainment to misclassification. Giving credence to our numbers, however, is the report by McDonald et al., who noted near-doubling of CDAD US hospital discharges, from 98,000 in 1996 to 178,000 in 2003 (2
). Additionally, while exhibiting a similar absolute rise, CDAD primary diagnosis admissions as a fraction of all CDAD hospitalizations remained constant. Although it is possible that the observed rise in CDAD hospitalizations is due to changes in coding practices, evidence of an increase in microbiologic detection of this pathogen argues against this explanation for our observations (8
The incidence in adult CDAD-related hospitalizations increased substantially in the period 2000–2005. In view of the aging US population, this rapid pace of growth is alarming. If this rate of rise, along with the increase in virulence and diminished susceptibility to antimicrobial drug treatments, persists, CDAD will result not only in a considerable strain on the US healthcare system (9
) but also in rising numbers of deaths related to this disease (1
). Allocation of public health resources aimed at prevention of CDAD is necessary to mitigate this growing epidemic. Research into the best preventive strategies, such as limiting the use of antimicrobial agents in both human disease and the food supply (11
), is a public health imperative.