Rising tularemia cases demand action: CDC highlights diagnostic breakthroughs and calls for targeted efforts to protect vulnerable communities.

Report: Tularemia — United States, 2011–2022. Image Credit: Kateryna Kon / Shutterstock

In a recent study published in the journal Morbidity and Mortality Weekly Report, scientists from the United States (U.S.) Centers for Disease Control and Prevention (CDC) examined the demographic patterns, geographic distribution, and trends in the incidence of tularemia, a rare bacterial disease caused by Francisella tularensis. This disease can infect humans through various routes, such as insect bites, contaminated food or water, and inhalation.

Background

Tularemia is a zoonotic disease caused by the bacterium Francisella tularensis. Humans can contract the disease through contact with infected animals, insect bites, inhaling contaminated particles, or consuming polluted water. Symptoms vary widely, including fever, localized infections, or severe respiratory conditions.

Although the disease is treatable with antibiotics, tularemia can lead to significant health challenges, especially in cases of delayed diagnosis. Historically, the disease has been reported across most U.S. states, with some regions and demographic groups experiencing higher incidence rates. Notably, environmental and occupational exposures, as well as proximity to wildlife, contribute to these patterns. Furthermore, populations in the central states and American Indian or Alaska Native communities often face a disproportionately higher burden of disease.

While surveillance efforts and laboratory advancements have improved case detection in recent decades, the disease remains underreported and poorly understood. The lack of a preventive vaccine and varying clinical presentations further underscore the importance of enhanced public health measures and medical education to reduce its impact on vulnerable populations.

Reported tularemia cases, by county of residence — United States, 2011–2022

About the study

The present study utilized tularemia surveillance data reported to the CDC from 2011 to 2022. The cases were classified into confirmed or probable categories based on clinical and laboratory criteria. Confirmed cases were determined based on the isolation of F. tularensis or the antibody titers showing at least a four-fold change between serum samples from acute and convalescent stages.

Additionally, probable cases were identified through a single elevated antibody titer or detection of the bacterium through fluorescent assay or polymerase chain reaction (PCR). The inclusion of PCR methods in 2017 marked a significant advancement in diagnostic criteria. The researchers analyzed data for annual incidence rates across demographic groups, geographic locations, and case classifications.

Furthermore, the U.S. Census Bureau population estimates were used to calculate rates per 100,000 individuals. The study also reviewed temporal trends in tularemia cases and assessed the impact of surveillance criteria changes and laboratory diagnostic advancements over the years.

Geographic distribution analysis included county-level mapping, while demographic data focused on age, gender, race, and ethnicity. This comprehensive analysis enabled the identification of patterns and disparities in disease incidence. Differences in case detection methods, state reporting practices, and laboratory technologies were also considered to contextualize observed trends.

The researchers also discussed some of the study’s limitations, including potential underreporting, variability in state-level surveillance, and the impact of external factors such as the coronavirus disease 2019 (COVID-19) pandemic on data collection. These factors highlight the need for consistent and robust surveillance practices across states. The findings aimed to inform public health strategies for reducing tularemia incidence and improving diagnostic practices. The investigation adhered to ethical standards and federal laws.

Major findings

The study found that the incidence of tularemia in the U.S. increased by 56% during 2011–2022 compared to the previous decade. A total of 2,462 cases were reported during this period, with 40% classified as confirmed and 60% as probable. The increase in probable cases is partly attributed to advancements in diagnostic methods, such as the shift to enzyme-linked immunosorbent assays (ELISA), which are more sensitive but less specific than earlier agglutination tests.

The annual incidence rates varied from 0.041 to 0.064 per 100,000 population, with notable geographic and demographic disparities. Four central states—Arkansas, Missouri, Kansas, and Oklahoma—accounted for half of all cases, indicating a concentration of infections in these regions. Children between the ages of 5 and 9 and males aged 65 to 84 exhibited the highest age-specific incidence rates.

American Indian or Alaska Native populations experienced rates approximately five times higher than White populations, indicating significant health disparities. Sociocultural and occupational activities, as well as the concentration of Native American reservations in central states, likely contribute to this increased risk. Additionally, seasonal patterns showed that most cases occurred between May and September, likely reflecting increased exposure to vectors during warmer months.

Furthermore, the temporal analysis revealed that probable cases consistently outnumbered confirmed cases since 2015, with divergence beginning after the 2017 expansion of laboratory criteria, including PCR detection. While improved detection methods and increased case reporting likely contributed to the rise in incidence, the researchers believe other factors, such as environmental or behavioral changes, may also play a role.

The study highlighted the need for targeted prevention strategies for at-risk populations and regions. The findings also underscored the importance of educating healthcare providers to enhance early diagnosis and effective treatment, particularly for providers serving tribal populations with limited access to specialized medical resources.

Conclusions

The study brought attention to an increasing trend in tularemia incidence across the U.S., driven by better detection methods and rising case reports. The geographic and demographic disparities observed in the study highlighted the vulnerable populations requiring targeted prevention and education efforts.

Addressing these disparities through tailored public health initiatives, focused clinical education, and improved laboratory testing practices can reduce health inequities and enhance outcomes. The CDC researchers believe that addressing these disparities through public health initiatives, early diagnosis, and timely treatment can mitigate the disease’s impact, reduce health inequities, and improve outcomes for those most at risk.