Alpha-Gal Syndrome Why We Still Don't Know How Many People Are Affected

Alpha-gal syndrome — a meat allergy triggered by a tick bite — occupies a strange position among American health threats: it is "an emerging, tick bite–associated allergic condition characterized by potentially life-threatening hypersensitivity" (CDC 2023), yet "in the absence of national surveillance, the geographic distribution and number of cases are largely unknown" (CDC 2023). In plain terms, no federal system requires doctors or laboratories to report cases, so no one keeps a running national count. The condition has grown from a handful of documented patients into what one 2025 review described as a syndrome "estimated to impact up to 450 000 individuals in the US" (JAMA 2025) — yet that figure is itself an estimate built on extrapolations from a single commercial laboratory's test data, not from any coordinated public health count.

The result is a condition that may be among the most common tick-borne illnesses in the country while remaining functionally invisible to the systems designed to track disease.

How Common Is Alpha-Gal Syndrome — Why Don't We Know the Real Numbers?

The short answer is that no one is required to count. As the CDC (Centers for Disease Control and Prevention) noted in 2023, "AGS is not a nationally notifiable condition, and understanding epidemiologic trends relies on laboratory-based surveillance" (CDC 2023). A "nationally notifiable condition" is a disease that doctors and labs must report to public health authorities; without that mandate, the only way to estimate how widespread AGS is, is to comb through whatever blood-test results commercial labs happen to generate. A 2024 infodemiology study — research that tracks how people search online for health information — put it bluntly: "The alpha-gal syndrome is not a reportable or notifiable condition and was only granted a separate International Classification of Diseases 10th Revision (ICD-10) code for diagnostic identification in 2022." (PMC 2024) ICD-10 codes are the standard labels doctors and insurers use to record diagnoses; until 2022, AGS did not even have its own code, meaning earlier records lumped it in with generic allergy categories.

Without mandatory reporting, researchers have been forced to piece together prevalence from lab data. The largest such effort used test results from a single reference laboratory. As the CDC reported:

"Together with suspected AGS cases identified from alpha-gal sIgE tests and panels in this study, a total of 110,229 suspected cases were documented during 2010–2022." — CDC, 2023. Geographic Distribution o...

That figure — documented cases from one lab — is the floor, not the ceiling. The CDC itself acknowledged that "these results almost certainly underestimate the number of persons seeking testing and persons receiving positive test results" (CDC 2023), because patients who never get tested never get counted. The agency's own estimate of the true burden is far higher:

"Assuming 70%–90% of these suspected cases (77,161–99,207) are clinically compatible AGS cases, and assuming that 22%–80% of all persons with AGS have access to knowledgeable HCPs who submit a specimen for alpha-gal sIgE testing, 96,000–450,000 persons in the United States might have been affected by AGS since 2010." — CDC, 2023. Geographic Distribution o...

That range is wide because the CDC has to make two assumptions: how many people with positive blood tests actually have the disease, and how many people with the disease ever reach a doctor who knows enough to order the test in the first place. A 2025 review summarized the situation starkly: "According to the CDC, there were over 100,000 cases nationally diagnosed by a single reference laboratory in the US from 2010 to the end of 2022; the CDC's estimate of cases totaled 450,000." (IJGM 2025) Even that upper bound, the review continued, is likely too low, because "even these numbers are likely an underestimate as AGS is neither nationally reportable nor mandated as reportable in all states" (IJGM 2025).

For a deeper look at state-level reporting systems across tick-borne diseases, see State Tick Disease Reporting Requirements.

The trajectory of confirmed cases

What the available data do show is a condition whose documented numbers have grown dramatically in just over a decade. In the earliest reports, "In the US alone, the number of confirmed cases of AGS has risen from only 12 in 2009 to 34,000 in 2019." (FrontCellInfectMicrobiol 2021) That is a roughly 2,800-fold increase over ten years. A 2022 HHS (U.S. Department of Health and Human Services) report to Congress made the comparison even more explicit: "In 2009, there were 24 reported cases of AGS; however, more recent data documented more than34,000 cases from 2010 to 2018 in the United States alone, and AGS was identified as the leading cause of anaphylaxis in a southeastern registry of patients." (HHS 2022) Anaphylaxis is the most severe form of allergic reaction — the kind that can close airways or drop blood pressure to dangerous levels — and being the leading cause of it in any region is a substantial public-health signal.

The CDC's own data from 2017 through 2022 showed the curve continuing to rise. "Overall, 90,018 (30.5%) persons received a positive test result in the study period, and the number of persons with positive test results increased from 13,371 in 2017 to 18,885 in 2021." (CDC 2023) Each year brought approximately 15,000 new suspected cases. Yet even those annual gains raise a question the CDC itself could not answer: "Whether the increasing numbers of suspected AGS cases seen in this study are an indication of increased awareness, increasing emergence, or both remains unclear." (CDC 2023) In other words, the agency cannot say whether more people are actually getting sick or whether more doctors are finally recognizing what was already there.

Sensitization is far more common than disease

One of the complications that makes counting AGS especially difficult is the gap between sensitization — having antibodies to alpha-gal — and clinical disease. Being "sensitized" means a person's immune system has produced alarm molecules to a substance, but those alarms do not always cause symptoms when the person is exposed. Large numbers of people in tick-endemic areas carry detectable alpha-gal IgE (immunoglobulin E, the antibody type that drives allergic reactions) without developing allergic reactions to meat. A 2020 clinical review noted that "In certain geographic areas and in populations with high tick exposure, the level of sensitization can be 15-35% but this does not represent clinical AGS, which appears to occur in 1-8% of sensitized individuals." (T&F 2020) Put another way: in the hardest-hit regions, up to a third of people show the antibody, but only a small slice of those people ever react to a hamburger.

A 2021 German study made the point even more sharply: among forest service employees and hunters, "elevated IgE levels >0.1 kUA/L against α-Gal were present in 35% of this group, but also in 15% of an age-matched control group from the general population." (FrontAllergy 2021) The unit kUA/L is simply how labs measure antibody concentration in blood; the threshold >0.1 is a routine cutoff for "detectable." In the tick-exposed cohort, "only 5% of α-Gal IgE-positive subjects suffered from a clinical α-Gal syndrome." (FrontAllergy 2021) So even among people whose jobs put them face-to-face with ticks, only one in twenty of those who tested positive actually had the meat allergy.

This wide gap between sensitization and clinical illness means that a positive blood test alone does not confirm the disease. The CDC's geographic study acknowledged as much — while noting that "recent unpublished surveillance data that examined positive alpha-gal sIgE test results at commercial laboratories showed that approximately 90% of persons with a positive test result did have clinical symptoms consistent with AGS and that they were classified as having confirmed AGS." (CDC 2023) sIgE stands for "specific IgE" — a blood test that measures antibodies aimed at one particular target, in this case alpha-gal. The discrepancy between general-population sensitization studies and clinically-directed testing underscores how sensitive the prevalence estimate is to who gets tested and why: when only patients with suspicious symptoms get tested, the positive rate looks high; when researchers test the general public, most positives turn out to be silent.

A 2023 review synthesized the available data: "Up to 2–3% of the residents in the most affected areas have AGS, and 35% or more of some populations in the U.S., e.g., in the southeastern states, are sensitized to alpha-gal, and the CDC's estimate places AGS as the 10th most common food allergy in the U.S., appearing to be the leading cause of adult-onset food-allergy/anaphylaxis in certain datasets." (MDPI 2023) That last point is worth pausing on: among adults who develop a new food allergy, alpha-gal is the most common cause in some U.S. data — a striking finding for a condition that almost no national tracking system records. Even regional testing thresholds themselves are uncertain — as the same review noted, "The cut-off of alpha-gal IgE testing might be different in different geographic areas based on background sensitization. Hence, some larger population-based studies are needed." (MDPI 2023)

Who gets tested, and who doesn't

The data that do exist are shaped by which patients managed to get a blood test — and those patients are not representative of the population at large. The CDC reported:

"Because numerous barriers affect access to testing, these test results do not equitably reflect the U.S. populations affected by AGS. Studies have documented that most patients seeking and receiving sIgE testing were more likely to report being non-Hispanic White, with higher incomes, and higher educational attainment (5,10)." — CDC, 2023. Geographic Distribution o...

In other words, the people who appear in the lab data tend to be wealthier, more educated, and more likely to be white than the country as a whole — so the case map reflects who has access to specialty medicine as much as who has the disease. The path to testing itself is a bottleneck. The CDC noted that "The need for repeated clinical visits and access to specialized practitioners, which might span several years before a diagnosis is made , also creates a testing barrier for patients." (CDC 2023) An earlier patient-driven study put a finer point on this disparity: "The high education level of our sample raises questions about patients who successfully obtained diagnosis. Combined with the characteristics of those who were diagnosed relatively early, it suggests that more educated and determined patients are more likely to be diagnosed. Therefore, prevalence could be far more common." (PMC 2017)

The implications of diagnostic difficulty for individual patients are explored further in Alpha-Gal Misdiagnosis Rate.

Geography: concentrated but spreading

The geographic picture mirrors the reporting problem. The CDC found that suspected cases "predominantly occurred in counties within the southern, midwestern, and mid-Atlantic U.S. Census Bureau regions" (CDC 2023) — broadly the historical range of the lone star tick (Amblyomma americanum), the main species that triggers AGS. The highest raw numbers were concentrated in specific counties — "The highest numbers of suspected AGS cases were identified in counties within New York (Suffolk ) and Virginia (Bedford ); 4% of all suspected cases nationwide resided in Suffolk County, New York." (CDC 2023)

But the condition is not staying put. The CDC also found "focal clusters of cases in areas where there are no known established populations of lone star ticks, such as Minnesota and Wisconsin, although these data are relatively sparse, and more information is needed to validate these as cases acquired in those areas." (CDC 2023) Cases are showing up where the suspected vector is not supposed to live, raising the possibility that other tick species can sensitize people too. The 2025 Maine surveillance study underscored this expansion: in a state with no established lone star tick ("AGS is not a reportable condition in Maine" (CDC-EID 2025)), voluntary surveillance efforts identified "57 confirmed or suspect cases of AGS" (CDC-EID 2025) — apparently linked instead to Ixodes scapularis, the blacklegged or "deer" tick familiar from Lyme disease.

Globally, the picture is even less complete. Cases have been "described across the world, including North, Central and South America, Europe, Southern and Western Africa, East and South Asia, Australia and New Zealand." (PMC 2020) Yet in some regions, the relationship between sensitization and disease remains unexplained. In Africa, for instance, "numerous African countries that conducted seroprevalence studies found that individuals have IgE antibodies specific to α-gal. However, there was no indication of any allergic reactions after red meat consumption." (FrontCellInfectMicrobiol 2021) Seroprevalence studies measure how many people in a population carry a given antibody — and in this case, the antibodies are there but the allergy is not, a puzzle researchers have not yet solved.

The Knowledge Silo

The surveillance gap is not only a reporting problem — it is a knowledge-distribution problem. A 2025 rapid review documented a pattern in which most of the clinical detective work on AGS remained within a single medical specialty: "most of the clinical detective work in identifying and describing AGS has in the past been accomplished by allergists and published in allergy/immunology journals. So while the disease crossed several fields, the literature did not, and knowledge generally remained within allergy and immunology." (IJGM 2025) A patient who shows up at a gastroenterologist with stomach pain hours after dinner, or at a cardiologist with a racing heart at 2 a.m., is unlikely to encounter a doctor who has read the AGS literature — because that literature lives in journals those doctors do not routinely read.

The numbers are striking. Of 219 studies the authors collected, "allergy and immunology journals comprised 42% (92). General journals were the next largest number at 36 (16%), with gastroenterology at 17 (8%) and infectious disease and dermatology at 11 each (5% each)." (IJGM 2025) The review argued that this siloing has direct consequences for patients:

"The most urgent finding is that the literature continues to be disseminated primarily through the field of allergy/immunology. Although situating publications in general journals is helpful, it only partially addresses the issue of dissemination if connections are not explicit across fields. The continuing siloing of knowledge into a single specialty helps to constrain provider knowledge, encouraging the use of default “idiopathic” diagnoses, and affecting how and when patients are diagnosed and how soon their disease can be effectively managed. The proportion of alpha-gal studies in specialties outside of allergy and immunology almost certainly contributes to the lack of provider awareness." — IJGM, 2025. Alpha-Gal Syndrome: Often...

The phrase "default 'idiopathic' diagnoses" in that quote refers to a label doctors use when they cannot identify a cause — idiopathic literally means "of unknown origin." When AGS is the real explanation but the doctor has never heard of it, the patient often goes home with an "idiopathic" reaction noted in their chart and no answer at all.

This pattern was not only academic. A CDC survey found that "Overall, 635 (42%) respondents had not heard of AGS, and another 530 (35%) reported that they were “not too confident” about their ability to diagnose or manage patients with AGS." (CDC 2023). Among those providers who were aware of the condition, "674 (78%) had not made a diagnosis of AGS in the previous year" (CDC 2023). Combined, those numbers mean roughly three out of four U.S. health care providers either do not know AGS exists or do not feel competent to recognize it. The connection between provider knowledge and the surveillance gap is direct: "The lack of HCP knowledge of AGS is likely to lead to undertesting, further hampering knowledge of the national prevalence of AGS." (CDC 2023) HCP stands for "health care provider" — doctors, nurse practitioners, and physician assistants — and when they do not order the test, the case never enters the lab data the CDC depends on.

Even in patient-driven settings, the information gap was palpable before the medical literature caught up. A 2017 study documented that "Reports of alpha-gal made their way into popular media before information on the allergy gained traction in the medical literature. It was discussed on national radio programs in 2011-2012, in Reader's Digest in 2013; in 2014, added to Wikipedia and WebMD (after a CBS news segment)." (PMC 2017) Patients and journalists knew this allergy existed before most of medicine did.

Mortality, Labeling, and What Else We're Missing

The downstream consequences of the surveillance gap extend beyond case counts. Because systematic tracking does not exist, researchers cannot determine basic epidemiological facts — including how often AGS kills people. A 2017 patient-driven study warned that "Because diagnosis rarely occurs, it is likely related deaths are not detected; therefore, population prevalence and mortality rate are unknown." (PMC 2017) If a person with undiagnosed AGS dies from anaphylaxis after a steak, the death certificate is unlikely to mention alpha-gal, and the case never enters any tally.

Management is also complicated by structural gaps unrelated to diagnosis. For patients who are identified, avoidance of triggers is "made difficult by the lack of adequate labeling for mammalian-derived sources in foods, medications, and vaccines" (T&F 2020) — meaning that food, drug, and vaccine labels do not consistently flag mammalian ingredients, so a patient cannot tell from the label whether a product is safe. One review characterized AGS as "an atypical, underdiagnosed vector-borne allergy that presents clinical implications beyond expected due to the presence of α-Gal in various animal-derived medical products, hindering the treatment of several other pathologies." (PMC 2022) In practical terms, alpha-gal turns up in places patients would not think to check — gel capsules, certain heart-valve replacements, some cancer drugs — and a patient with an unrecognized allergy to it can have a reaction during treatment for an entirely unrelated condition. A Psychiatric Times analysis argued that "Mandated reporting of all drug ingredients would go a long way in managing their care and alleviating stress for both patients and their providers." (PsychT 2024)

A patient survey conducted by Tick-Borne Conditions United captured how patients themselves prioritize these gaps. When asked about their most pressing concerns, respondents identified:

"• 89% Lack of healthcare provider knowledge • 79% Ingredient labeling on food and pharmaceuticals • 36% Funding for additional research on Alpha-gal • 35% Other • 21% Lack of non-mammal ingredient vaccinations • 21% Broader tick testing to capture additional conditions • 15% Need for treatment, prevention, and signage in public places • 8% Coping in the workplace and school environment • 5% Mammal-free tick repellents and yard treatments • 5% Lack of understanding and support from family" — TBCU, 2019, pp. 2–3. Alpha-gal Patient Perspec...

The dominance of "lack of healthcare provider knowledge" at 89% reflects a problem that surveillance infrastructure alone cannot fix — but that surveillance infrastructure would help to quantify and address. If the CDC could publish state-level case counts the way it does for Lyme disease, every primary-care doctor in a high-incidence county would know to keep AGS on the list of possibilities.

What Happens Next

The trajectory points in one direction. The HHS Tick-Borne Disease Working Group (TBDWG) — a federal advisory body that reports to Congress on tick-borne disease policy — recommended in 2022 a concrete step: "Potential Action 1.1: Improve regional surveillance and reporting of tick-borne diseases, including alpha-gal syndrome, and expand physician and public education to ensure that health care providers consider the potential for tick-borne diseases in their patients." (HHS 2022) A 2022 CDC-affiliated study noted that the Working Group had already "issued a report to Congress emphasizing the importance of AGS and need for better understanding of the disease that impacts quality of life." (CDC 2022) A recommendation, however, is not the same as a mandate — Congress and the agencies still have to act on it before national reporting becomes a reality.

Meanwhile, the number of people affected continues to grow. A 2022 review of U.S. lab data found "a 6-fold increase in the number of positive tests from 2011 to 2018, suggesting that sensitization rates to alpha-gal in the US may be rising." (PMC 2022) Six times as many positive tests in seven years is a steep climb, even allowing for greater awareness driving more testing. The 2023 CDC report concluded:

"If testing trends continue, and the geographic range of the lone star tick continues to expand, the number of AGS cases in the United States is predicted to increase during the coming years, presenting a critical need for synergistic public health activities including 1) community education targeting tick bite prevention to reduce the risk for acquiring AGS, 2) HCP education to improve timely diagnosis and management, and 3) improved surveillance to aid public health decision-making." — CDC, 2023. Geographic Distribution o...

And with climate-driven expansion of tick habitats, a 2022 review warned that "With climate change, the tick-host paradigm will shift towards an increasing number of AGS cases in new regions worldwide, which will pose new challenges for clinicians in the future." (PMC 2022) Warmer winters and changing land use are letting lone star ticks survive farther north and west than they used to, which means clinicians in regions that have never seen AGS will increasingly encounter it.

The surveillance gap is not a problem waiting to emerge. It is the current condition — one where, as one clinical review summarized, "many providers are not aware of the condition, and patients may suffer for years before an accurate diagnosis." (CDC 2022)

Sources

    Not medical advice. See a healthcare provider for medical decisions. Medical Disclaimer