Unusual Serum sickness, vasculitis, nephrosis, neuritis, encephalitis Symptoms start several days to weeks after the insect sting.
of children, include localized pain, swelling, and erythema at the sting site that usually subside within 24 hours. Large local reactions occur in approximately 10% of patients. They are usually late-phase, IgE-mediated reactions, with large swelling, contiguous to the sting site that develops over 24 to 48 hours and resolves within 2 to 7 days. Virtually all individuals with large local reactions have similar reactions with subsequent stings. Systemic reactions are IgE mediated and occur in 1% of children. They can be mild and nonlife-threatening with cutaneous symptoms only or life-threatening with respiratory, cardiovascular, or neurologic symptoms of anaphylaxis (see Chapter 81). Toxic reactions may result if a person receives a large number of stings (50 to 100). Symptoms include malaise, nausea, and emesis resulting from the toxic effects of the venom. Unusual reactions, such as vasculitis, nephrosis, neuritis, serum sickness, and encephalitis, rarely are associated with insect stings (Table 83-1).
A positive skin test to Hymenoptera venom extract demonstrates the presence of venom-specific IgE in the context of a positive sting reaction history and helps identify specific insects to which an individual is allergic. Venom-specific IgE antibodies also may be measured by in vitro serum tests. Both testing methods should be considered complementary because neither test alone detects all patients with insect sting allergy. Future reactions correlate more with past individual patterns than the level of sensitivity of venom skin testing or serum specific IgE testing.
A history of an immediate systemic reaction is necessary before venom testing and immunotherapy should be considered.
Identification of the offending insect is often unreliable. Honeybee stings may be identified by the stinger that remains in place. Vespid stings are usually unprovoked and occur at summer’s end when the insects are more aggressive.
Local reactions should be treated by cleaning the site,applying cold compresses, and administering oral antihistamines and analgesics. Occasionally large local reactionsmay be mistaken for cellulitis. Infection is unlikely if reaction occurs within 24 to 48 hours after a sting. Treatment iswith an oral corticosteroid for 4 to 5 days rather than oralantibiotics.
Treatment of systemic reactions is guided by the severity of the reaction, but epinephrine is the cornerstone of therapy and should be administered without delay. Antihistamines may be administered concurrently with epinephrine. Corticosteroids should be given to prevent recurrent or prolonged symptoms. For severe reactions, intravenous fluids and epinephrine, oxygen, and respiratory support in an intensive care unit may be needed. After acute care of a systemic sting reaction, patients should be provided an epinephrine autoinjector, referral to an allergist/immunologist, and instructions on prevention of insect stings.
At least 50 to 100 fatalities per year in the United States are attributed to insect sting reactions. Most deaths (80%) occur in adults older than 40 years of age, and only 2% occur in individuals younger than 20 years of age. Approximately one half of deaths occur in persons without any history of a prior sting reaction.
Successfully avoiding the stinging insect is the most important prognostic factor. More than 85% of adults who complete 5 years of immunotherapy tolerate challenge stings without systemic reactions for 5 to 10 years after completion.
Measures to reduce the chance of accidental sting include exterminating infested areas; not eating or drinking outdoors; wearing long pants and shoes; and avoiding brightly colored clothing, fragrances, or hairspray when outdoors. Common insect repellents are not effective against Hymenoptera.