What type of swab (swab sample) is needed to test a lesion for a sexually transmitted disease (STD)?

Swab Type and Collection for STD Lesion Testing

Use a cotton-wool or Dacron swab to collect specimens from the lesion base, and request nucleic acid amplification testing (NAAT/PCR) with pathogen typing, as this provides the highest sensitivity and specificity (>90%) for diagnosing sexually transmitted infections causing genital lesions. 1, 2

Optimal Swab Selection

• Cotton-wool or Dacron swabs are the standard collection tools for STD lesion testing, and calcium alginate swabs should be avoided as they can interfere with viral recovery 1, 3
• The swab should be placed on an aluminum shaft for urethral or cervical specimens to allow proper insertion depth 1

Collection Technique by Lesion Type

For Vesicular Lesions (HSV suspected):

• Open vesicles with a sterile needle first, then collect the vesicular fluid content with the swab 1, 2, 3
• Vigorously swab the base of the lesion to obtain epithelial cells, which are required for adequate examination and quality assessment 1, 2
• Collect specimens as early as possible in the disease course, as vesicular lesions yield significantly higher positivity rates than ulcerative or healing lesions 2, 3

For Ulcerative Lesions (syphilis, chancroid suspected):

• Cleanse the lesion with sterile gauze and saline before specimen collection 1
• Swab the ulcer base directly without contaminating with surface genital skin 1
• For syphilis specifically, the swab can be applied directly to a slide for darkfield microscopy or direct fluorescent antibody (DFA) testing, though NAAT is increasingly preferred 1

Testing Recommendations by Pathogen

Herpes Simplex Virus (HSV):

• Request NAAT/PCR with HSV typing (HSV-1 vs HSV-2 differentiation), as this is critical for counseling—12-month recurrence rates differ dramatically: HSV-2 (90%) versus HSV-1 (55%) 1, 2, 3
• NAAT is more sensitive than culture, especially for non-vesicular, ulcerative, or recurrent lesions 1, 2

Syphilis (Treponema pallidum):

• Collect specimens for DFA-Treponema pallidum or NAAT from the lesion base 1
• Always obtain serology (nontreponemal RPR/VDRL and treponemal-specific tests) in parallel, as serologic testing is essential for syphilis diagnosis 1

Chancroid (Haemophilus ducreyi):

• Swab the lesion base for Gram stain, culture, or NAAT 1
• Transport specimens to the laboratory immediately at room temperature 1

Human Papillomavirus (HPV/Genital Warts):

• Visual inspection is the primary diagnostic method for genital warts; high-risk HPV testing is not recommended for wart diagnosis 1
• For cervical screening in women ≥30 years, use an endocervical brush into liquid cytology medium for high-risk HPV testing 1

Critical Specimen Transport Requirements

• HSV specimens: Place swab in viral transport medium (VTM) or universal transport medium (UTM); transport at room temperature if <2 hours, refrigerate if longer 1
• Syphilis DFA slides: Allow slide to dry completely before placing in holder and transporting to laboratory 1
• Chancroid specimens: Transport immediately to laboratory at room temperature 1
• Consult your laboratory before collection regarding specific NAAT requirements, as specimen source allowances and turnaround times vary by assay 1

Common Pitfalls to Avoid

• Do not rely on clinical diagnosis alone without laboratory confirmation, as genital HSV is difficult to differentiate from syphilis, chancroid, and other causes of genital ulceration 1, 2
• Do not use serology for acute lesion diagnosis of HSV, as type-specific antibody tests cannot distinguish active from past infection 1, 3
• Do not collect specimens from healed lesions, as sensitivity drops dramatically; if lesions have healed, type-specific serology may be the only option 2, 3
• Do not test only one pathogen—the CDC recommends that all patients with genital lesions should be evaluated with serologic testing for syphilis, diagnostic tests for HSV, and HIV screening, as multiple simultaneous infections are common 1