Physical Exam Documentation of Insect Bites
When documenting an insect bite on physical exam, describe the location, size, morphology (including presence of central punctum, vesicles, or pseudopustules), distribution pattern (clustered, linear, or circular), surrounding tissue changes (erythema, warmth, induration), and any systemic signs, as these features distinguish benign local reactions from infectious complications and life-threatening conditions.
Essential Components to Document
Primary Lesion Characteristics
- Location and distribution: Note whether lesions appear on exposed areas versus covered areas, as this helps identify the arthropod type 1, 2
- Size: Measure the diameter of erythema and induration; large local reactions are defined as swelling greater than 10 cm in diameter contiguous to the sting site 3, 4
- Morphology: Document specific features:
- Presence of a central punctum (small red dot at bite center, highly suggestive of bed bugs) 1
- Vesicles, bullae, or urticarial wheals in sensitized individuals 1
- Sterile pseudopustules developing within 24 hours (pathognomonic for fire ant stings) 5, 3, 4
- Presence of barbed stinger with attached venom sac (indicates honeybee sting) 5
Distribution Patterns
- Linear or curvilinear arrangement: Classic for bed bug bites, often described as "breakfast, lunch, and dinner" pattern when three lesions appear in a row 1
- Circular pattern: Multiple stings in a circular distribution suggest fire ants 5
- Clustered lesions: Common with multiple bites from various arthropods 1
Local Tissue Response
- Erythema: Document the diameter and whether it is expanding 5, 2
- Edema/swelling: Note if increasing over 24-48 hours (typical for large local reactions) or if present on upper eyelid (highly suggestive of bed bugs) 4, 1
- Warmth: Presence suggests possible secondary bacterial infection, not allergic inflammation 5, 4
- Tenderness: Progressive increasing pain may indicate cellulitis rather than simple bite reaction 4, 6
- Induration: Measure the diameter of any firm tissue 2
Signs of Infection vs. Allergic Reaction
Critical distinction: Most early swelling after insect bites is IgE-mediated allergic inflammation, not infection 4. Document:
- Infection indicators: Progressive redness, increasing pain, purulent discharge, fever, warmth, and tenderness to palpation 5, 4
- Allergic reaction indicators: Rapid onset swelling (24-48 hours), pruritus without progressive pain, absence of purulence 4, 7
Systemic Signs Requiring Immediate Documentation
- Vital signs: Fever, tachycardia, hypotension 5, 3
- Skin findings beyond bite site: Generalized urticaria, angioedema, flushing 3, 7
- Respiratory: Stridor, wheezing, dyspnea 3, 7
- Cardiovascular: Hypotension, chest pain, arrhythmias 5, 3
- Gastrointestinal: Nausea, vomiting, diarrhea, cramping 5, 7
- Neurological: Dizziness, confusion, seizures 7, 2
Common Pitfalls to Avoid
Misdiagnosing Allergic Swelling as Cellulitis
The most common error is treating early allergic swelling as bacterial cellulitis, leading to unnecessary antibiotic use 3, 4. Large local reactions are IgE-mediated and self-limited, typically increasing in size for 24-48 hours and taking 5-10 days to resolve 3, 4. True cellulitis presents with progressive warmth, tenderness, and systemic signs 5, 4.
Missing Fire Ant Stings
The pathognomonic sterile pseudopustule developing within 24 hours distinguishes fire ant stings from other bites 5, 3, 4. This is not an infection and should not be treated with antibiotics 4.
Overlooking Tick-Borne Disease
When fever, rash (especially involving palms/soles), thrombocytopenia, or elevated liver enzymes accompany a suspected insect bite, consider Rocky Mountain Spotted Fever, as 40% of cases have no recalled tick exposure 3. This carries significant mortality risk and requires immediate empiric doxycycline 3.
Failing to Document Systemic Symptoms
Generalized urticaria, angioedema, respiratory symptoms, or cardiovascular symptoms require immediate epinephrine administration 3, 4. Delayed epinephrine is associated with fatal outcomes 3.
Special Considerations
Travel History Context
Recent travel to endemic regions (tropical/subtropical areas) with pain disproportionate to the bite appearance should raise suspicion for myiasis (botfly larvae), which may be mistaken for cellulitis 6. Point-of-care ultrasound can identify foreign bodies in such cases 6.
Timeline Documentation
Note when the bite occurred relative to symptom onset, as this helps distinguish immediate hypersensitivity reactions from delayed infectious complications 5, 4. Large local reactions peak at 24-48 hours, while cellulitis typically develops days later with progressive symptoms 4.