Anesthesia Key

CHAPTER 167

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Fire Ant Stings

Presentation

Usually the patient has experienced multiple burning stings (the “fire” in fire ant) and is seeking help because of local swelling, itching, and/or pain. Twenty-four hours after the initial wheal and flare at the sting site, there is formation of a small (2 mm), sterile, round pustule on an erythematous base, which is virtually pathognomonic for a fire ant sting (Figure 167-1). These lesions often occur in clusters. Sometimes there are large local reactions, and it is not unusual for an entire extremity to be affected. Systemic reactions in previously sensitized individuals are analogous to those caused by hymenopteran stings (see Chapter 171).

Figure 167-1 Fire ant sting. (Adapted from White G, Cox N: Diseases of the skin, ed 2. St Louis, 2006, Mosby.)

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The appearance of the sting site changes over time. Within 1 week, the pustule often ruptures, forming a small crust or superficial ulcer, which then may become secondarily infected. After 1 month, small visible scars will be persistent (Figure 167-2).

Figure 167-2 A, Thirty minutes poststing. B, One hour poststing. C, Twenty-four hours poststing. D, Seventy-two hours poststing. E, One week poststing. F, One month poststing. (Adapted from Goddard J, Jarratt J, de Castro FR: Evolution of the fire ant lesion. JAMA 284:2162-2163, 2000.)

What To Do:

signs of an immediate systemic allergic reaction (anaphylaxis), such as decreased blood pressure, generalized urticaria or erythema, or wheezing. Treat with 0.3 to 0.5 mL of intramuscular epinephrine 1:1000 (may repeat every 10 to 15 minutes, as needed, to reverse the symptoms) along with boluses of IV normal saline (see Chapter 171).

Relieve itching and burning with cold compresses.

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Treat minor reactions with topical steroids, such as triamcinolone (Aristocort A), 0.1% or 0.5% cream, or desoximetasone (Topicort) emollient cream, 0.25% or gel 0.05%. Dispense 15 g to apply tid or qid.

When swelling is severe or there are other signs and symptoms of an allergic component to the stings, and there are no signs of infection or other contraindications to systemic corticosteroids, prescribe a brief course of prednisone, 40 to 60 mg qd for 4 to 5 days, or give one dose of triamcinolone (Aristocort Forte, Kenalog-40), 40 mg IM.

If there are signs of infection with surrounding swelling, tenderness, heat, and erythema, treat aggressively with cephalexin (Keflex), 500 mg qid, cefadroxil (Duricef), 500 mg bid × 10 days, or azithromycin (Zithromax), 500 mg, then 250 mg qd × 4 days. Always consider the possibility of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infection (see Chapter 166).

Advise all these patients about avoiding future fire ant stings by wearing shoes (not sandals) when walking outside and to add socks, long pants, and work gloves when working outside. If there are infestations of fire ants around homes or businesses, have professional exterminators help with their removal.