What is the treatment for a patient with a history of allergies who has been stung by a fire ant?

Treatment of Fire Ant Stings in Patients with Allergy History

For a patient with a history of allergies who has been stung by a fire ant, immediately administer intramuscular epinephrine 0.3-0.5 mg in the anterolateral thigh if any systemic symptoms develop, as delayed epinephrine administration is associated with fatal outcomes. 1, 2, 3

Immediate Management Based on Reaction Type

Local Reactions Only

• Apply cold compresses to reduce pain and swelling 2
• Administer oral antihistamines for pruritus 2
• Provide oral analgesics for pain control 2
• Do NOT prescribe antibiotics unless secondary infection develops (progressive redness, purulent discharge, fever, increasing pain), as early swelling is IgE-mediated allergic inflammation, not infection 4, 2
• For severe large local reactions (>10 cm diameter), consider a brief course of oral corticosteroids, though controlled trial evidence is limited 1, 4, 2

Systemic Reactions (Anaphylaxis)

• Immediately inject epinephrine 0.3-0.5 mg intramuscularly in the anterolateral thigh - this is the drug of choice 1, 2, 3
• Transport to emergency department with supportive therapy (oxygen, IV fluids, monitoring) 1, 5
• Administer corticosteroids and antihistamines as adjunctive therapy 5
• Provide bronchodilators if bronchospasm present 5

The presence of sterile pseudopustules developing within 24 hours is pathognomonic for fire ant stings and helps confirm the diagnosis. 4, 5

Post-Acute Management Algorithm

Step 1: Prescribe Emergency Epinephrine

• All patients with a history of allergies who have been stung should carry epinephrine auto-injectors for future use 1
• Educate on proper use and indications for self-administration 1

Step 2: Refer to Allergist-Immunologist

Referral is recommended for all patients with systemic reactions or those with coexisting conditions/medications that might complicate future reactions 1, 2

Step 3: Allergy Testing (Performed by Allergist)

• Perform skin testing with imported fire ant whole-body extract (the only available reagent for fire ant testing) 1
• Begin with skin prick testing; if negative, proceed to intracutaneous testing starting at 1:1,000 wt/vol concentration 1
• Wait at least 6 weeks after the sting reaction before testing if initial tests are negative, as venom-specific IgE may be temporarily non-reactive in the first few weeks 1, 2
• If skin tests remain negative after 6 weeks despite severe reaction, perform in vitro IgE testing and baseline serum tryptase measurement 1

Immunotherapy Decision Algorithm

Indications for Fire Ant Immunotherapy

Immunotherapy with imported fire ant whole-body extract is recommended for all patients who have experienced a systemic reaction to a fire ant sting AND have positive skin test or serum-specific IgE results 1

Special consideration for children: Because fire ant hypersensitivity natural history in children with only cutaneous manifestations is not well-established, and children in endemic areas have increased sting risk, immunotherapy might be considered even for isolated cutaneous reactions 1

When Immunotherapy is NOT Necessary

• Children ≤16 years with only cutaneous systemic reactions (urticaria, flushing, angioedema) without respiratory or cardiovascular symptoms 1
• Patients with only large local reactions, unless they have frequent unavoidable exposure 1

Duration of Immunotherapy

Once initiated, continue immunotherapy for at least 3-5 years 1

Consider extended or indefinite therapy for high-risk patients:

• Near-fatal reaction before immunotherapy 1
• Systemic reaction during immunotherapy 1
• Increased baseline serum tryptase levels 1
• Frequent unavoidable exposure 1

The optimal duration of fire ant immunotherapy is less well-defined than for other Hymenoptera venoms, and some experts recommend continuing until skin tests become negative 1

Critical Pitfalls to Avoid

• Never delay epinephrine administration in systemic reactions - fatal sting reactions are associated with delayed or absent epinephrine use 1, 2
• Do not misdiagnose allergic swelling as cellulitis - this leads to unnecessary antibiotic use 4, 2
• Do not perform skin testing within 6 weeks of the reaction if initial tests are negative - results may be falsely negative 2
• Do not assume negative skin and in vitro tests completely exclude future anaphylaxis risk - rare cases (<1%) can still occur, possibly due to non-IgE mechanisms or underlying mastocytosis 1

Patient Education Essentials

• Educate on insect avoidance strategies (fire ants nest in mounds of freshly disturbed soil, often along roadsides in southeastern states) 1
• Recommend medical identification bracelet or necklace 1
• Ensure familiarity with epinephrine auto-injector technique 1