Wound swab - viral

Role

Viral wound/lesion swabbing (PCR, the modern standard over older viral culture) confirms viral aetiology in vesicular or ulcerative skin/mucosal lesions - most commonly for suspected herpes simplex or varicella-zoster virus infection
A routine, widely performed test given the high prevalence of HSV and VZV reactivation/infection presenting with vesicular or ulcerative lesions across dermatology, sexual health, and general practice

PCR has largely superseded viral culture given substantially higher sensitivity and faster turnaround - viral culture requires viable virus and intact vesicles, with sensitivity dropping considerably once lesions have crusted, while PCR remains sensitive even on later-stage or crusted lesions

Technique: unroof an intact vesicle where possible and swab the vesicle base/fluid (the site of highest viral titre) rather than surrounding skin - swabbing a crusted or healing lesion still has reasonable PCR sensitivity but is less optimal than an early, intact vesicle
Send in viral transport medium (or dry swab depending on local laboratory PCR protocol) - confirm the correct collection method with the local laboratory before sampling

Confirmed HSV -> aciclovir/valaciclovir, guided by clinical severity and recurrence pattern (episodic vs suppressive therapy)
Confirmed VZV -> aciclovir/valaciclovir, with attention to timing (most effective within 72 hours of rash onset) and specific consideration of disseminated/ophthalmic zoster requiring more urgent/aggressive treatment
Result also informs infection control precautions (e.g. isolation for disseminated zoster in an inpatient setting) and, for genital HSV, partner counselling

Herpes simplex virus (primary and recurrent), varicella-zoster virus (chickenpox and shingles), disseminated/ophthalmic zoster (higher-stakes presentations requiring urgent treatment), antiviral timing windows

Swabbing technique substantially affects yield - unroofing an intact early vesicle and sampling the base/fluid gives the highest diagnostic yield, while PCR's superior sensitivity over older culture methods means a reasonably useful result can still be obtained from a later-stage or crusted lesion when an early vesicle isn't available

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