CDC study highlights growing threat of tularemia in central US

CDC study highlights growing threat of tularemia in central US

Rising Tularemia Cases Require Action: CDC Highlights Diagnostic Breakthroughs and Calls for Targeted Efforts to Protect Vulnerable Communities.

In a study recently published in the journalMorbidity and Mortality Weekly ReportScientists at the US 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 byFrancisella 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 bacteriumFrancisella tularensis. People can become infected with the disease through contact with infected animals, insect bites, inhalation of contaminated particles, or consumption of contaminated water. Symptoms vary widely and include fever, local infection, or severe respiratory illness.

Although the disease is treatable with antibiotics, tularemia can cause significant health problems, especially if diagnosis is delayed. Historically, the disease has been reported in most U.S. states, with some regions and populations experiencing higher incidence rates. Environmental and occupational exposures as well as proximity to wild animals primarily contribute to these patterns. Additionally, populations in the central states and Native American or Alaska Native communities often face a disproportionately higher burden of disease.

While surveillance efforts and laboratory advances in recent decades have improved case detection, the disease remains underreported and poorly understood. The lack of a preventive vaccine and the variable clinical symptoms highlight the importance of increased public health and medical education measures to reduce the impact on vulnerable populations.

Reported cases of tularemia, 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. Cases were classified into confirmed or probable categories based on clinical and laboratory criteria. Confirmed cases were determined based on isolationF. tularensisor the antibody titers show at least a fourfold change between serum samples from acute and convalescent stages.

In addition, probable cases were identified by a single elevated antibody titer or detection of the bacterium by fluorescence assay or polymerase chain reaction (PCR). The inclusion of PCR methods in 2017 represented a significant advance in diagnostic criteria. Researchers analyzed data on annual incidence rates across demographic groups, geographic locations and case classifications.

Additionally, U.S. Census Bureau population estimates were used to calculate rates per 100,000 people. The study also examined temporal trends in tularemia cases and evaluated the impact of changes in surveillance criteria and advances in laboratory diagnostics over the years.

Geographical 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 differences in disease incidence. Differences in case detection methods, state reporting practices, and laboratory technologies were also considered to contextualize observed trends.

Researchers also discussed some of the study's limitations, including possible 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 results aimed to provide public health strategies to reduce tularemia incidence and improve diagnostic practices. The investigation adhered to ethical standards and federal laws.

Key insights

The study found that the incidence of tularemia in the United States increased by 56% between 2011 and 2022 compared to the previous decade. A total of 2,462 cases were reported during this period, of which 40% were classified as confirmed and 60% as probable. The increase in probable cases is due in part to advances in diagnostic methods, such as the switch to enzyme-linked immunosorbent assays (ELISA), which are more sensitive but less specific than previous agglutination tests.

Annual incidence rates varied between 0.041 and 0.064 per 100,000 population, with significant geographic and demographic differences. Four central states — Arkansas, Missouri, Kansas and Oklahoma — accounted for half of all cases, suggesting a concentration of infections in those regions. Children aged 5 to 9 years and men aged 65 to 84 years had the highest age-specific incidence rates.

Rates in American Indian or Alaska Native populations were about five times higher than in white populations, indicating significant health disparities. Sociocultural and occupational activities, as well as the concentration of Indian reservations in central states, likely contribute to this increased risk. Furthermore, seasonal patterns showed that most cases occurred between May and September, likely due to increased exposure to vectors in the warmer months.

In addition, temporal analysis revealed that the number of probable cases has consistently exceeded the number of confirmed cases since 2015, with divergence beginning after the expansion of laboratory criteria in 2017, including PCR detection. While improved detection methods and increased case reporting have likely contributed to the increase in incidence, 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 vulnerable populations and regions. The findings also highlighted the importance of training healthcare providers to improve early diagnosis and effective treatment, particularly for providers serving Indigenous populations who have limited access to specialized medical resources.

Conclusions

The study highlighted an increasing trend in the incidence of tularemia in the United States, driven by better detection methods and increasing case reports. The geographic and demographic differences observed in the study highlighted the need for targeted prevention and education efforts at vulnerable populations.

Addressing these disparities through tailored public health initiatives, targeted clinical training, and improved laboratory testing practices can reduce health disparities and improve outcomes. CDC researchers believe that eliminating these disparities through public health initiatives, early detection and timely treatment can mitigate the impact of the disease, reduce health disparities and improve outcomes for those most at risk.

Sources: