Multisite evaluation of fire ant venom immunotherapy safety and efficacy

Abstract

Background: Imported fire ant (IFA) venom immunotherapy (VIT) is the only disease-modifying treatment reported to be effective at decreasing the risk of systemic reactions (SRs) to IFA stings.

Objective: Our aims were to determine the baseline rates of IFA sensitization in subjects, describe IFA VIT prescribing patterns across the military health system (MHS), and retrospectively evaluate the safety and efficacy of IFA VIT.

Methods: We prospectively compared IFA sensitization in participants with and without an SR to flying Hymenoptera venom. Separately, IFA VIT prescription records were extracted from a centralized repository, and rates were described across the MHS. Additionally, we retrospectively reviewed the clinical course of patients being treated with IFA VIT at 11 military treatment facilities.

Results: The in vitro IFA sensitization rates in our prospective cohort ranged from 19.1% to 24.1%. Sensitization rates did not differ statistically between the subjects with or without an SR to flying Hymenoptera venom. We found that 60.9% of all MHS IFA VIT prescriptions (491 of 806) were from the 11 facilities in this study. We retrospectively identified 137 subjects actively undergoing IFA VIT. Among the subjects actively undergoing IFA VIT, 28 reported an SR to IFA venom and repeat stings by IFAs after reaching VIT maintenance, and 85.7% (24 of 28) of the subjects noted symptoms no worse than a large swelling reaction after a repeat IFA sting. Notably, only 2.9% of the subjects (4 of 137) had an SR due to VIT.

Conclusion: This study's results align with those of prior IFA sensitization reports. A substantial proportion of patients undergoing IFA VIT experienced protection against anaphylaxis with reexposure, with relatively few adverse events.

Keywords: Hymenoptera; ImmunoCap; Imported fire ant; anaphylaxis; hypersensitivity; immunotherapy; venom.

Fig 1

Multisite partnership sites and location. Location of all facilities in our study. Blue indicates a Navy facility, green indicates an Army facility, and purple indicates a joint facility.

Fig 2

Stacked Venn diagram comparing source of subjects. Gray indicates all subjects in USACAEL (5 years), green indicates subjects within DoD facilities only (5 years), and blue indicates subjects within partnership facilities (5 years). Yellow indicates those subjects in the ALX group in partnership facilities during the first quarter of 2021, and red indicates those subjects in the ALX group who had an SR before VIT, reached maintenance, and were stung after maintenance (the STX group). Q, Quarter.

Fig 3

Subject adverse events. Comparison of notable subject subsets as defined in Table III. Pink indicates subjects who used epinephrine for an SR to IFA VIT treatment specifically after maintenance (2 of 101 [2%]), and cyan indicates subjects who had SR to IFA VIT treatment specifically (4 of 137 [2.9%]).

Fig 4

Efficacy and sting challenge reaction distribution. IFA sting reaction distribution for subjects who reached maintenance and had an SR to IFA before VIT as defined in Table IV. Yellow indicates a reaction with no more than local irritation (19 of 28 [67.9%]), orange indicates large swelling (5 of 28 [17.8%]), salmon indicates a systemic cutaneous reaction (2 of 28 [7.1%]), and red indicates anaphylaxis (2 of 28 [7.1%]).