D625 Task 1 Epidemiological Analysis Example

A Tick Bite and a Hamburger: Analyzing Alpha-Gal Syndrome Data in a Composite Southeastern County and Evaluating Whether Its Tick Bite Prevention Program Works

Student Name

Leavitt School of Health, Western Governors University

D625: Principles of Epidemiology, Task 1

Course Instructor

Month Day, Year

A Tick Bite and a Hamburger: Analyzing Alpha-Gal Syndrome Data in a Composite Southeastern County and Evaluating Whether Its Tick Bite Prevention Program Works

The Condition

Alpha-gal syndrome is an allergic condition in which a person develops antibodies to galactose-alpha-1,3-galactose, a sugar found in most mammalian meat and in products made from mammals, after certain tick bites. In the United States, bites from the lone star tick are the main recognized cause. Reactions typically begin two or more hours after eating red meat or other mammal products and range from hives and stomach upset to anaphylaxis; there is no cure. Laurel County, a composite rural county of about 70,000 people in the southeastern United States with extensive woodland and many outdoor workers, has asked its health department whether the condition is increasing locally and whether its tick bite prevention program is working.

Quantitative Data and What They Can Show

National data establish the pattern. A CDC analysis of alpha-gal antibody test results from the commercial laboratory that performed nearly all such testing found that, from 2017 to 2022, 90,018 of 295,400 people tested, 30.5%, had a positive result. Positive results climbed from 13,371 people in 2017 to 18,885 in 2021, and the counties with the most suspected cases lay across the South, the lower Midwest and the mid-Atlantic, a pattern that follows the known range of the lone star tick (Thompson et al., 2023). A person living in one of those counties is therefore far more likely to be tested and to test positive than a person living in the Northwest or Southwest, where the tick is rare.

Laurel County's data come from the same kind of source. The state obtained laboratory results for county residents, showing 212 people with positive tests over six years, rising from 24 in the first year to 47 in the last. Converted to a rate using the county population as the denominator, positive results rose from about 34 to about 67 per 100,000 residents per year. The number of people tested also rose, from 71 to 158, while the share testing positive fell slightly, from 34% to 30%.

These numbers must be read carefully. A positive antibody test is a suspected case, not a confirmed diagnosis, because some people with antibodies have no symptoms. The counts are not true incidence: they include only people whose clinicians thought to order the test. And because testing more than doubled, much of the rise in positive results could reflect greater awareness rather than more disease, an example of detection bias. The falling positivity rate supports that interpretation, although it is also consistent with testing being extended to people at lower risk. Alpha-gal syndrome is not nationally notifiable, so there is no case report system that would add clinical information.

Qualitative Data

Numbers cannot show why people go undiagnosed. The health department interviewed 12 county residents with diagnosed alpha-gal syndrome and six local clinicians. Patients described months or years of unexplained reactions, often waking at night with hives or vomiting, and visits to several clinicians before anyone connected their symptoms to the meal hours earlier. Several had been told their reactions were anxiety. Clinicians said they had learned about the condition from patients. These accounts match national findings: in a survey of 1,500 U.S. health care providers, 42% had never heard of alpha-gal syndrome, and among those who had, fewer than one-third knew how to diagnose it (Carpenter et al., 2023). The qualitative data explain part of the quantitative pattern: underrecognition keeps counts low, and rising awareness pushes them up.

Applying Epidemiologic Methods and Concepts

Several concepts shape how the county should interpret and extend its data. Case definition: the department should distinguish a suspected case, a positive test, from a probable case, a positive test with compatible symptoms, and track both. Incidence and prevalence: because the condition can persist for years and testing captures people who may have been sensitized long before, the laboratory counts mix new and existing cases. Confounding: outdoor work, rural residence and hunting are linked to one another and to tick exposure, so maps of positive results by area cannot show which factor matters most. An ecological fallacy would occur if the county concluded that every resident of a high-rate area is at high risk. To study risk factors directly, a case-control study comparing residents with probable alpha-gal syndrome to similar residents without it could estimate odds ratios for occupation, outdoor recreation, pet ownership and repellent use.

Evaluating the Tick Bite Prevention Program

For three years, the county's program has distributed brochures at parks and clinics, posted trail signs about tick checks and run a spring social media campaign. Its annual reports count activities: brochures printed, signs installed, posts viewed. They do not show whether anyone was bitten less, and the rising laboratory counts cannot be used as an outcome measure because they are driven by testing. By an epidemiologic standard, the program's effectiveness is unknown.

The program can be strengthened with interventions that have evidence and with outcomes that can be measured. For outdoor workers, factory-treated permethrin clothing reduced tick bites by 58% over two years in a randomized, placebo-controlled trial among outdoor workers in the northeastern United States (Mitchell et al., 2020); the county could offer treated clothing to its parks, road and forestry crews and partner with large outdoor employers. For evaluation, the county should measure self-reported tick bites and prevention behaviors in a short annual survey of residents and workers, track the positivity rate and the number of probable cases rather than raw positive counts, and compare trends with similar counties that have no program. Clinician education should be added and evaluated separately, since it is expected to increase testing and diagnoses at first, which should be reported as improved detection rather than program failure.

Conclusion

Alpha-gal syndrome appears to be increasing in Laurel County, but the data show rising recognition as clearly as rising disease. Interpreting them requires attention to denominators, case definitions and detection bias, and qualitative data explain much of what the numbers cannot. The county's prevention program has been active but not evaluated; adding interventions with evidence, such as treated clothing for outdoor workers, and measuring bites and behaviors rather than brochures would let the county know whether it is preventing the condition as well as finding it.

References

Carpenter, A., Drexler, N. A., McCormick, D. W., Thompson, J. M., Kersh, G., Commins, S. P., & Salzer, J. S. (2023). Health care provider knowledge regarding alpha-gal syndrome: United States, March-May 2022. Morbidity and Mortality Weekly Report, 72(30), 809-814. https://doi.org/10.15585/mmwr.mm7230a1

Mitchell, C., Dyer, M., Lin, F.-C., Bowman, N., Mather, T., & Meshnick, S. (2020). Protective effectiveness of long-lasting permethrin impregnated clothing against tick bites in an endemic Lyme disease setting: A randomized control trial among outdoor workers. Journal of Medical Entomology, 57(5), 1532-1538. https://doi.org/10.1093/jme/tjaa061

Thompson, J. M., Carpenter, A., Kersh, G. J., Wachs, T., Commins, S. P., & Salzer, J. S. (2023). Geographic distribution of suspected alpha-gal syndrome cases: United States, January 2017-December 2022. Morbidity and Mortality Weekly Report, 72(30), 815-820. https://doi.org/10.15585/mmwr.mm7230a2