Descriptive Temporal Epidemiology of Tularemia Using Case Reports and Hospitalization Data in the United States, 2000–2022

Tularemia is a well-known zoonotic disease around the world, with particularly high rates in certain geographic areas of the U.S. Though the disease is regularly reported, it is classified as a rare condition owing to the relatively low number of cases detected annually. Interestingly, however, the number of cases in the U.S. has shown a positive upward trend through time. The aim of this study was to summarize, interpret, compare, and contextualize temporal trends in tularemia epidemiology at the national scale within the U.S. utilizing long-term data sets encompassing the 23-year span from 2000 to 2022. We used two secondary data sets: (1) case data reports from the National Notifiable Disease Surveillance System (NNDSS) of the Centers for Disease Control and Prevention (CDC) and (2) the National Inpatient Sample (NIS) of hospitalization discharge records. In addition to investigating patterns, we were interested in the utility of using hospital discharge records as a means of indirect epidemiological surveillance of this rare disease. Both data sets highlight the high variability in annual cases through time but underscore the highest risk of disease among patients classified as White and male, as well as the extraordinarily high rates among American Indian/Alaska Native populations, particularly those with pulmonary tularemia disease. Descriptive epidemiological summaries and statistical comparisons are provided across the time series for sex, age, ethnoracial identity, and geography; hospitalization characteristics are also described. Our desire to use case rates from hospitalization records as a surrogate for CDC case incidence rates did not provide the desired precision, though hospital discharge records do provide valuable and useful information necessary to estimate general high-risk groups for tularemia through time.