Trends in gastroenteritis-associated mortality in the United States, 1985–2005: variations by ICD-9 and ICD-10 codes

Worldwide, gastrointestinal infections are a major, and often preventable, cause of mortality. In much of the developing world, mortality due to gastrointestinal infections disproportionately impacts children and is often associated with poor hygienic conditions (e.g., contaminated food or water and person-to-person transmission) [1]. In contrast, in the United States the elderly have a higher mortality rate due to gastrointestinal infections [2],[3]. Trends in gastroenteritis-associated mortality are changing over time [4]. These changes may be due to several factors including the development of antibiotic resistant strains of certain pathogens, changing healthcare practices, the prevalence of immunosuppressive conditions, and demographic changes such as a growing elderly population.

Rates of enteric infection and mortality due to enteric infections steadily dropped during the 20th century due to disinfection of drinking water and improved hygiene practices. However, in the 1990s and early 2000s, mortality rates in the United States began to increase [2],[3]. This is consistent with a rising proportion of Americans at increased risk for severe consequences due to enteric infections, including the elderly and those that are immunocompromised [5],[6]. Data from the Foodborne Diseases Active Surveillance Network (FoodNet), which collects data for 10 U.S. states, together with passive surveillance data were used to estimate that 31 major pathogens cause 1,351 deaths (90% CrI 712-2,268) annually [7]. In addition, an estimated 1,686 deaths (90% CrI 369-3,338) annually are due to foodborne illness from unspecified pathogenic agents [8]. This represents only a fraction of all deaths due to enteric infections which can also occur through waterborne and person-to-person transmission. Improved diagnostics, accuracy, and completeness of coding for deaths due to enteric infections may be causes for the demonstrated increasing trend.

Mortality records are coded using the International Classification of Disease (ICD), which was recently modified. In 1999, coding for mortality changed from using the ICD-9 scheme to ICD-10. The ICD-10 system is more detailed with approximately 8,000 categories for disease classification compared to about 5,000 categories in the ICD-9 system [9]. Few studies have demonstrated that the changes from ICD-9 to ICD-10 coding can affect trends in mortality. A study in Italy demonstrated that there was little variability between the two schemes for the larger disease groups, such as diseases of the circulatory system, however, the variability was higher for ‘minor’ disease groups such as infectious diseases and respiratory diseases [10]. A study focusing on respiratory disease mortality in the United Kingdom demonstrated that there was a 22% decrease in deaths assigned to respiratory disease under the ICD-10 coding scheme [11]. In the Southeastern United States, a study found that the change to ICD10 underestimated mortality due to heart disease and cerebrovascular disease and overestimates deaths due to diabetes [12]. In the U.S. it has been shown that implementing ICD-10 has variable effects on the discontinuity in trend; for some leading causes of death, such as influenza and pneumonia the discontinuity is substantial [13].

In this study we examine rates and trends in gastroenteritis-associated mortality for a 21-year period from 1985 to 2005, during which the ICD-10 coding scheme, was implemented by categories of pathogens (viral, bacterial, protozoal). The ICD-10 coding scheme differs in several aspects from the ICD-9 scheme, including more detailed classification. Of importance for this study, coding rules and rules for selecting the underlying cause of death have been changed in the ICD-10 system [13]. Therefore, in this paper our analysis is stratified based on the ICD system used and assesses changes in ICD coding on gastroenteritis associated mortality.

This post was last modified on November 27, 2024 4:10 am