What is the recommended test for diagnosing herpes simplex?

Recommended Diagnostic Tests for Herpes Simplex Virus

Nucleic acid amplification tests (NAATs), specifically PCR, are the gold standard for diagnosing herpes simplex virus infections due to their superior sensitivity and specificity compared to other methods. 1, 2

Primary Diagnostic Approach

• PCR testing is the preferred method for HSV detection with sensitivity 11-71% superior to viral culture, allowing for both detection and typing of HSV in a single reaction 3, 1
• Real-time PCR offers significant advantages: faster results (approximately 2 hours), simplified performance conditions, and lower contamination risk compared to traditional PCR 3
• PCR allows less strict sample transportation conditions compared to viral culture, making it more practical in clinical settings 3
• PCR can detect HSV DNA for an average of 6.8 days in lesions compared to only 2.6 days with viral culture, significantly increasing diagnostic yield 4

Sample Collection for Optimal Results

• For vesicular lesions: open vesicles with a sterile needle and collect content with a swab 3
• For ulcerative lesions: sample the base of the ulcer (PCR can detect HSV DNA in 15 of 17 days versus only 3 of 17 days by viral culture) 4
• Collection sites depend on presentation:
  • Vesicular rash on skin/mucous membranes: NAAT or antigen detection 3
  • Male urethra: NAAT or antigen detection 3
  • Female cervix/urethra: NAAT or antigen detection 3
  • Conjunctiva: NAAT or antigen detection 3
  • Spinal cord fluid: NAAT 3

Alternative Diagnostic Methods

• Viral culture: traditional method with 90% isolation rate from vesicular/pustular lesions, but only 70% from ulcerative lesions and 27% from crusting lesions 3

  • Results typically available in 24-72 hours but may take up to 5 days 3, 1
  • Requires strict sample transportation conditions (refrigeration) 1
  • Allows virus typing and antiviral sensitivity testing 3

• Antigen detection methods (immunofluorescence or enzyme immunoassays):

  • Sensitivity ≥95% compared to viral isolation for symptomatic patients 3
  • Most commercial assays do not differentiate between HSV types 3
  • Should not be the first choice when PCR is available 2

Importance of HSV Typing

• HSV typing is essential for counseling and prognosis 3, 2
• Type-specific testing to distinguish HSV-1 from HSV-2 is always recommended 5
• Up to 50% of first-episode genital herpes cases are caused by HSV-1 2
• Recurrences and subclinical viral shedding are less frequent with genital HSV-1 than HSV-2 2

Clinical Pitfalls to Avoid

• Do not rely solely on clinical diagnosis without laboratory confirmation 2
• Avoid using Tzanck smears due to low sensitivity and specificity 1, 2
• Do not use HSV molecular assays in the absence of genital ulcers 2
• Widespread screening for HSV antibodies is not recommended 2
• Type-specific serology should only be used for detecting asymptomatic infections in high-risk individuals 2
• Recognize that PCR can detect HSV DNA even when viral culture is negative, particularly in ulcerative lesions 4, 6

Quality Control Considerations

• Each DNA extraction and analysis should include internal positive controls and negative controls 3
• Certified reference panels should be used for intra- and inter-laboratory quality control 3
• First-episode infections typically show higher viral quantities than recurrent infections, which may affect test sensitivity 6