title: A systematic review of the epidemiology and interaction of herpes simplex virus types 1 and 2.
abstract: OBJECTIVE
  To explore epidemiological evidence about the interaction of herpes simplex virus (HSV) 1 and HSV-2 infections.
  
  
  METHODS
  A systematic review was undertaken of published epidemiological studies describing the pattern of HSV-1 or HSV-2 by age, and the coincidence of the two viral infections.
  
  
  RESULTS
  In cross sectional studies the unadjusted odds of HSV-2 are greater in those with HSV-1 infection in study populations categorised as "low risk" (p = 0.06) and across European populations (p = 0.001). This was not evident in "high risk" populations or in the United States. This increased risk of HSV-2 in those with HSV-1 infection does not agree with the results of prospective studies where there is a non-significant trend towards a lower risk of HSV-2 infection associated with previous HSV-1 infection.
  
  
  CONCLUSIONS
  "Low risk" and European populations have a relatively low HSV-2 seroprevalence and infection is more concentrated in those with characteristics putting them at high risk for both HSV-1 and HSV-2. This confounding could mask any protective effect of HSV-1, which is hinted at, but not demonstrated, in prospective and adjusted studies.
authors.affiliation: Department of Infectious Disease Epidemiology, Imperial College Faculty of Medicine, St Mary's Campus, Norfolk Place, London W2 1PG, UK. k.looker@imperial.ac.uk
authors.forename: K J
authors.initials: KJ
authors.lastname: Looker
authors.forename: G P
authors.initials: GP
authors.lastname: Garnett
mesh_terms: D006561:Herpes Simplex / Q000453:epidemiology* / Q000821:virology; D018259:Herpesvirus 1, Human; D018258:Herpesvirus 2, Human; D006801:Humans; D016017:Odds Ratio; D015995:Prevalence