How to identify and treat common bites and stings
A thorough history and physical are key to proper diagnosis and treatment following a patient’s encounter with an insect, arachnid, or other arthropod.
PRACTICE RECOMMENDATIONS
❯ Recommend that patients use an insect repellent, such as an over-the-counter formulation that contains DEET, picaridin, or PMD (a chemical constituent of Eucalyptus citriodora oil) to prevent flea bites. C
❯ Prescribe nonsedating oral antihistamines as first-line symptomatic treatment of mild-to-moderate pruritus secondary to an insect bite. C
❯ When indicated, refer patients for venom immunotherapy, which is approximately 95% effective in preventing or reducing severe systemic reactions and reduces the risk of anaphylaxis and death. C
Strength of recommendation (SOR)
A Good-quality patient-oriented evidence
B Inconsistent or limited-quality patient-oriented evidence
C Consensus, usual practice, opinion, disease-oriented evidence, case series
There are also risk factors for a systemic sting reaction:
- A sting reaction < 2 months earlier increases the risk of a subsequent systemic sting reaction by ≥ 50%.9
- Among beekeepers, paradoxically, the risk of a systemic reaction is higher in those stung < 15 times a year than in those stung > 200 times.10
- Patients with an elevated baseline serum level of tryptase (reference range, < 11.4 ng/mL), which is part of the allergenic response, or with biopsy-proven systemic mastocytosis are at increased risk of a systemic sting reaction.11
Presentation: Signs and symptomsvary with severity
Insect bites and stings usually cause transient local inflammation and, occasionally, a toxic reaction. Allergic hypersensitivity can result in a large local reaction or a generalized systemic reaction12:
- A small local reaction is transient and mild, develops directly at the site of the sting, and can last several days.13
- A large (or significant) local reaction, defined as swelling > 10 cm in diameter (FIGURE 1) and lasting > 24 hours, occurs in 2% to 26% of people who have been bitten or stung.14 This is an immunoglobulin (Ig) E–mediated late-phase reaction that can be accompanied by fatigue and nausea.12,13,15 For a patient with a large local reaction, the risk of a concomitant systemic reaction is 4% to 10%, typically beginning within 30 minutes after envenomation or, possibly, delayed for several hours or marked by a biphasic interval.16
- Characteristics of a systemic reaction are urticaria, angioedema, bronchospasm, large-airway edema, hypotension, and other clinical manifestations of anaphylaxis.17 In the United States, a systemic sting reaction is reported to occur in approximately 3% of bite and sting victims. Mortality among the general population from a systemic bite or sting reaction is 0.16 for every 100,000 people,2 and at least 40 to 100 die every year in the United States from anaphylaxis resulting from an insect bite or sting.18
- The most severe anaphylactic reactions involve the cardiovascular and respiratory systems, commonly including hypotension and symptoms of upper- or lower-airway obstruction. Laryngeal edema and circulatory failure are the most common mechanisms of anaphylactic death.19
Bees and wasps
Hymenoptera stinging insects include the family Apidae (honey bee, bumblebee, and sweat bee) and Vespidae (yellow jacket, yellow- and white-faced hornets, and paper wasp). A worker honey bee can sting only once, leaving its barbed stinger in the skin; a wasp, hornet, and yellow jacket can sting multiple times (FIGURE 2).2
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