Herpes simplex virus (HSV)

Herpes simplex virus (HSV)

Infection: Herpes; herpes simplex virus (HSV) infection

Brief description:
  • Virus that causes cold sores (HSV 1), and genital herpes (HSV 1 or 2).
  • Most people infected with HSV are asymptomatic and don’t get recurrences.
  • Genital herpes during pregnancy should be discussed with a specialist.
Did you know?
  • Genital herpes has been typically associated with HSV 2 infection, however HSV 1 is also responsible for a significant proportion of genital infection.
  • HSV 2 tends to recur more frequently than HSV 1, but be less severe.
Who should I test?
  • Testing recommended for a first episode of genital herpes to establish the diagnosis.
  • Testing not required for recurrences of genital herpes, or for cold sores, unless atypical features with a potential differential diagnosis.
  • Mimics to consider: syphilis if genital ulcer (although syphilis generally painless).
Test of choice:

Request HSV PCR

Viral swab of base of lesion for HSV PCR (need to obtain vesicle fluid or cellular material on swab)

  • Good sensitivity – a negative result on an adequately collected sample makes the diagnosis very unlikely
  • Excellent specificity – a positive result confirms the diagnosis

Note: swabs run for HSV PCR in our laboratory are run for VZV PCR in parallel, as these viruses can mimic each other.

Tests to avoid/specialist tests:


  • Has a very limited role in the diagnosis of HSV.
  • Having positive HSV serology is common in the general population. A positive serological test cannot confirm that a lesion is due to HSV.
  • Serology usually takes many weeks to become positive after primary infection, so is not useful for diagnosis in this context.
  • The NZ Herpes Foundation recommend education rather than HSV serology in partners of positive patients due to false positive and negative results seen with HSV serology.
  • Serology is indicated in pregnant women with a possible first episode of genital herpes from 30 weeks gestation, as it helps inform prophylaxis strategies to prevent neonatal infection.