Assessment of Bug Bites in Adults
For an adult presenting with a bug bite, immediately assess for systemic allergic reaction (anaphylaxis) and rule out life-threatening mimics like deep vein thrombosis if unilateral leg swelling is present, then evaluate the local reaction pattern and signs of true bacterial infection. 1, 2
Immediate Life-Threatening Assessment
Screen for Systemic Allergic Reaction
- Check for anaphylaxis signs: urticaria beyond the bite site, angioedema, respiratory symptoms (wheezing, stridor, dyspnea), cardiovascular symptoms (hypotension, tachycardia), gastrointestinal symptoms (nausea, vomiting, diarrhea), or neurological symptoms (dizziness, confusion) 1
- Administer epinephrine immediately if any systemic symptoms are present 3, 1
- Patients with prior systemic reactions to insect stings should already be carrying injectable epinephrine 3
Rule Out DVT in Unilateral Leg Swelling
- If the bite is on the leg with unilateral swelling, pain, tenderness, and warmth, obtain Doppler ultrasound immediately to rule out DVT before attributing symptoms solely to the insect bite 2
- Missing DVT can lead to pulmonary embolism and death, which far outweighs the minimal risk of delaying other treatment 2
Local Reaction Assessment
Characterize the Bite Pattern
- Identify the insect type based on appearance:
- Fire ant stings: sterile pseudopustules in a circular pattern, pathognomonic and NOT infected 3, 1
- Bed bugs: pruritic erythematous maculopapules in clusters or linear distribution, often "three in a row," with small red punctum at center 4
- Stinging insects (bees, wasps, hornets): may have visible stinger with attached venom sac in skin 3
Determine Reaction Severity
- Large local reactions: extensive swelling that increases over 24-48 hours and takes 5-10 days to resolve, representing IgE-mediated allergic inflammation, NOT infection 1
- Exaggerated reactions: vesicles, urticarial wheals, bullae, or nodules in previously sensitized individuals 4
- Timeline matters: symptoms within 24-48 hours of the bite with only swelling and warmth are consistent with allergic reaction rather than infection 2
Infection Assessment
Identify True Bacterial Infection Signs
Only 10-20% of bite wounds become infected, and antibiotics should ONLY be prescribed if clear signs of secondary bacterial infection are present: 1, 2
- Progressive redness that worsens despite symptomatic care 1
- Increasing pain over time 1
- Purulent discharge 1, 2
- Fever 1, 2
- Warmth and tenderness that progresses 1
- Lymphangitic streaking 2
Most swelling after insect bites is allergic mediator release, NOT infection—do not reflexively start antibiotics 1, 2
Special Populations and Referral Considerations
High-Risk Patients Requiring Specialist Referral
- Refer to allergist-immunologist if:
Venom Immunotherapy Candidates
- Adults with history of systemic reactions (beyond isolated cutaneous manifestations) and positive specific IgE testing should be considered for venom immunotherapy, which reduces risk of subsequent systemic reaction to less than 5% 3
- Testing may be temporarily non-reactive within the first few weeks after a systemic reaction and may require retesting in 6 weeks 3
Common Pitfalls to Avoid
- Do not prescribe antibiotics for typical insect bite swelling—the swelling is caused by allergic mediator release, not infection 1, 2
- Do not miss DVT by assuming all unilateral leg swelling is from an insect bite 2
- Do not delay epinephrine administration in systemic reactions—antihistamines and corticosteroids are NOT substitutes for epinephrine 3
- Do not rupture fire ant pseudopustules—leave intact and keep clean to prevent secondary infection 1