ATLANTA – The incidence of gastroenteritis-related deaths in the United States more than doubled from 1997 to 2007, largely because of Clostridium difficile and norovirus infections, mortality data from the National Center for Health Statistics show.
The apparent increase in C. difficile identified in this study is likely caused in part to increased recognition – and improved coding by physicians, but it also is likely because of a real increase resulting from the emergence of a hypervirulent and fluoroquinolone-resistant strain, Aron J. Hall, DVM, said at the International Conference on Emerging Infectious Diseases.
Photo Courtesy CDC/Charles D. Humphrey
On average, norovirus (shown here) contributed to nearly 800 deaths per year during the study period (3/1,000,000 person-years), but mortality rates surged about every 3 years by up to 50%; these surges coincided with outbreaks associated with emergent viral strains, Dr. Aron J. Hall said.
The elderly are disproportionately affected by these deadly infections, with those aged 65 years and older accounting for 83% of the gastroenteritis deaths during the study period, said Dr. Hall of the Centers for Disease Control and Prevention’s Viral Gastroenteritis Team.
"The mortality rate increases with increasing age, even within this older age group." These findings could help guide clinical management and development of candidate vaccines.
Between 1997 and 2007, all-cause gastroenteritis mortality increased from 25/1,000,000 person-years, to 57/1,000,000, which equates to an increase from about 7,000 to about 17,000 gastroenteritis-related deaths per year. The rate among those aged 65 years and older in 2007 was 259/1,000,000 person-years, Dr. Hall noted.
C. difficile was the leading cause of gastroenteritis-related death, and the incidence of C. difficile infection increased fivefold, from 10/1,000,000 in 1999-2000 to 48/1,000,000 in 2006-2007 – or from about 2,700 to 14,500 deaths per year.
Further, this study is the first to demonstrate that norovirus is likely the second leading infectious cause, Dr. Hall said.
On average, norovirus contributed to nearly 800 deaths per year during the study period (3/1,000,000 person-years), but mortality rates surged about every 3 years by up to 50%; these surges coincided with outbreaks associated with emergent viral strains, he explained.
As with C. difficile–related gastroenteritis deaths, most of these were in the elderly. However, a "small, but perhaps important" fraction of deaths occurred among children younger than age 5 years, Dr. Hall noted.
Seasonal variations also were apparent in this study, with C. difficile–associated deaths occurring most often during the spring months of March through May, and with norovirus-related deaths peaking in the winter months of December through February.
C. difficile and norovirus have emerged in recent years and are recognized as important contributors to gastroenteritis, but there have been limited data on deaths, Dr. Hall explained, adding that this is due in part to limited availability and/or sensitivity of clinical diagnostic assays, and also because deaths have historically not been coded specifically as being associated with a particular pathogen.
In fact, half of the gastroenteritis deaths included in the National Center for Health Statistics multiple cause of death mortality data are uncoded.
For this study, deaths with gastroenteritis listed as an underlying or contributing cause were included in the analysis, and an indirect attribution model was used to estimate the proportion of cause-unspecified gastroenteritis deaths that likely were due to specific causes. C. difficile, using this model, accounted for nearly 70% of gastroenteritis deaths.
The estimates of norovirus-associated gastroenteritis deaths in this study represent a 40% higher incidence than previously estimated based on extrapolation from community studies and studies from other industrialized countries, he added.
Gastroenteritis has long been recognized as an important contributor to mortality among children in developing countries, but less has been known about gastroenteritis-related mortality among adults and about the contributions of specific pathogens. These findings provide the first comprehensive analysis of data in more than 2 decades to characterize gastroenteritis deaths across all aged, he said.
The disease burden and seasonal patterns identified in this study could be helpful for the development of clinical management strategies, he said, adding that the mortality burden of these pathogens – particularly in the elderly – underscores the need for judicious use of antibiotics and proper infection control, as well as the need for effective interventions.
Dr. Hall noted that candidate vaccines are currently in development for both C. difficile and norovirus.
He reported having no relevant conflicts of interest.