Diagnostic testing for galactose-alpha-1,3-galactose, United States, 2010 to 2018

Abstract

Background: Alpha-gal syndrome (AGS) is an emerging immunoglobulin E (IgE)-mediated allergy to galactose-alpha-1,3-galactose (alpha-gal). The geographic distribution and burden of AGS in the United States are unknown.

Objective: To characterize alpha-gal IgE testing patterns and describe the trends and distribution from 2010 to 2018 in the United States.

Methods: This retrospective analysis included all persons tested for alpha-gal IgE antibodies by Viracor-IBT Laboratories (Lee's Summit, Missouri), the primary site of testing in the United States. Data included age and sex of person tested, specimen state of origin, collection date, and result value; persons with at least 1 positive test result (≥0.1 kU/L) were compared with negatives. Proportions tested and with positive test results were calculated using the US Census population estimates.

Results: Overall, 122,068 specimens from 105,674 persons were tested for alpha-gal IgE during July 1, 2010, to December 31, 2018. Nearly one-third (34,256, 32.4%) had at least 1 positive result. The number of persons receiving positive test results increased 6-fold from 1110 in 2011 to 7798 in 2018. Of those receiving positive test results, mean [SD] age was 46.9 (19.8) years; men were more likely to test positive than women (43.3% vs 26.0%). Arkansas, Virginia, Kentucky, Oklahoma, and Missouri had the highest number of persons who were tested and had a positive result per 100,000 population.

Conclusion: More than 34,000 persons, most presumably symptomatic, have received positive test results for IgE antibodies to alpha-gal, suggesting AGS is an increasingly recognized public health problem. The geographic distribution of persons who tested positive is consistent with exposure to Amblyomma americanum ticks.

Figure 1.

Number of persons who received positive test results per 100,000 population by age group and sex—United States, 2010 to 2018 (N = 33,999). Number of persons receiving positive test results per 100,000 was calculated using the average US Census population by age and sex during the study period. Mean estimates for each age group among males and females are represented by the clustered bars with 95% confidence intervals included for each mean estimate. No., number.

Figure 2.

Number of persons tested for alpha-gal IgE and (A) percent positive annually. (B) Number of positive per 100,000 population annually—United States, 2010 to 2018. The line of best fit for (A): slope = −2.6; 95% CI, −3.8 to −1.3; P = .003. The line of best fit for (B): slope = 0.3; 95% CI, 0.2–0.3; P <.001. Alpha-gal, galactose-alpha-1,3-galactose; CI, confidence interval; IgE, immunoglobulin E.

Figure 3.

Geographic distribution of alpha-gal IgE-positive persons per 100,000 population by state—United States, 2010 to 2018 (N = 15,091). Data are based on the state of origin of the first specimen testing positive for 15,091 persons. Number of persons tested and number of positive per 100,000 were calculated using the average US Census population by state during the study period. Legend categories were created using percentile distribution of data. Alpha-gal, galactose-alpha-1,3-galactose; IgE, immunoglobulin E; N/A, not applicable; No., number.