Geographic Distribution of Suspected Alpha-gal Syndrome Cases

United States, January 2017-December 2022

Julie M. Thompson, DVM, PhD; Ann Carpenter, DVM; Gilbert J. Kersh, PhD; Tyler Wachs; Scott P. Commins, MD; Johanna S. Salzer, DVM, PhD

Disclosures

Morbidity and Mortality Weekly Report. 2023;72(30):815-820.

Abstract and Introduction

Abstract

Alpha-gal syndrome (AGS) is an emerging, tick bite–associated allergic condition characterized by a potentially life-threatening immunoglobulin E (IgE)–mediated hypersensitivity to galactose-alpha-1,3-galactose (alpha-gal), an oligosaccharide found in most nonprimate mammalian meat and products derived from these mammals. Specific symptoms and severity of AGS vary among persons, and no treatment or cure is currently available. During 2010–2018, more than 34,000 suspected cases of AGS were identified in the United States, but current knowledge of where cases occur is limited. This study examined alpha-gal–specific IgE (sIgE) antibody testing results submitted to the commercial laboratory responsible for nearly all testing in the United States before 2022 to assess the geographic distribution and magnitude of this emerging condition. During January 1, 2017–December 31, 2022, a total of 357,119 tests were submitted from residences in the United States, corresponding to 295,400 persons. 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. Among 233,521 persons for whom geographic data were available, suspected cases predominantly occurred in counties within the southern, midwestern, and mid-Atlantic U.S. Census Bureau regions. These data highlight the evolving emergence of AGS and can be used to help state and local health agencies initiate surveillance and target public health outreach and health care provider education to high-risk localities.

Introduction

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Abstract and Introduction
Methods
Results
Discussion
References
Sidebar

*The national standardized case definition accepted in 2021 by the Council of State and Territorial Epidemiologist defined a confirmed case of AGS as being in a person who met the clinical criteria and had confirmatory laboratory evidence (serum or plasma sIgE to alpha-gal ≥0.1 international unit per milliliter or ≥0.1 kU/L). A suspected case of AGS was defined as being in a person who had confirmatory laboratory evidence with no clinical information available. https://ndc.services.cdc.gov/case-definitions/alpha-gal-syndrome-ags/
^†Until August 2021, Eurofins Viracor was the primary commercial laboratory offering alpha-gal sIgE testing. Few academic institutions and specialty allergy clinics offered testing before August 2021. Several commercial laboratories began offering alpha-gal sIgE testing in August 2021.

Table. Characteristics of persons who received testing for alpha-gal–specific immunoglobulin E — United States, January 1, 2017–December 31, 2022
Characteristic	No. (%)			RR (95% CI)	p-value^§
Characteristic	Total (N = 295,400)	Positive test result* (n = 90,018)	Negative test result^† (n = 205,382)	RR (95% CI)	p-value^§
Age, yrs, mean (SD)	43.1 (19.9)	48.2 (19.9)	40.8 (19.6)	NA	<0.001
Age group, yrs
0–9	12,332	2,478 (2.8)	9,854 (4.8)	Ref	<0.001
10–19	32,421	8,007 (8.9)	24,414 (11.9)	1.3 (1.2–1.4)
20–29	36,852	7,682 (8.5)	29,170 (14.2)	1.0 (1.0–1.1)
30–39	46,520	10,929 (12.1)	35,591 (17.3)	1.2 (1.2–1.3)
40–49	49,297	13,837 (15.4)	35,460 (17.3)	1.6 (1.4–1.6)
50–59	47,975	17,157 (19.1)	30,818 (15.0)	2.2 (2.1–2.3)
60–69	40,690	16,858 (18.7)	23,832 (11.6)	2.8 (2.7–3.0)
>70	29,304	13,064 (14.5)	16,240 (7.9)	3.2 (3.0–3.4)
Sex
Female	188,532	45,257 (50.3)	143,275 (69.7)	Ref	<0.001
Male	104,629	43,874 (48.7)	60,755 (29.6)	2.3 (2.2–2.3)
Unknown	2,239	887 (1.0)	1,352 (0.7)	2.1 (1.9–2.3)
Year
2017^¶	35,869	13,371 (14.9)	22,498 (11.0)	Ref	<0.001
2018	43,195	13,821 (15.4)	29,374 (14.3)	0.8 (0.8–0.8)
2019	57,327	17,372 (19.3)	39,955 (19.5)	0.7 (0.7–0.8)
2020	56,726	16,936 (18.8)	39,790 (19.4)	0.7 (0.7–0.7)
2021	66,106	18,885 (21.0)	47,221 (23.0)	0.7 (0.7–0.7)
2022	36,177	9,633 (10.7)	26,544 (12.9)	0.6 (0.6–0.6)

Abbreviations: IgE = immunoglobulin E; kU = kilounit; NA = not applicable; Ref = referent group; RR = risk ratio.
*At least one alpha-gal–specific IgE test result ≥0.1 kU/L in a patient was considered positive.
^†All alpha-gal–specific IgE test results <0.1 kU/L in a patient were considered negative.
^§P–values were calculated to identify significant difference in trends (age group or year) or interactions (sex) between those who received positive and negative test results; p<0.05 were considered statistically significant.
^¶Year was abstracted for the date of the first positive test result (for persons who received at least one positive test result) and the first negative test (for persons who only received negative test results).