title: [Asymptomatic infection by influenza AH1N1 virus in healthcare workers: MARBEGRIP study, preliminary results].
abstract: BACKGROUND
  The proportion of asymptomatic individuals infected by influenza AH1N1v varies depending on the studies. Health personnel were exposed to the AH1N1v virus due to their professional activity, thus an high seroprevalence to the virus could be expected in the absence of symptomatology. The objective of this study was to determine the prevalence of asymptomatic individuals serologically positive for influenza AH1N1v virus.
  
  
  METHODS
  A cohort based prospective study on hospital staff was proposed according to an hypothetic decreasing gradient of exposure to the virus, from emergency personnel to medical and surgical areas, and auxiliary staff other than emergency personnel. Serum sample from each participant was taken in September-October, 2009, November-December, 2009, and in April-May, 2010; and a health questionnaire was simultaneously filled out. Specific antibodies against influenza AH1N1v were detected by hemagglutination inhibition test. Eighteen hospitals (1,371 individuals) participated in the study.
  
  
  RESULTS
  Health questionnaire and serological results from four hospitals are available. A variable proportion of non vaccinated individuals showed positive serology (5.6-83%). Only 19.4% of subjects received vaccine, with a variable rate of positive serology (18.8-64.7%). Positive serology was significantly lower in non medical participants. In addition, vaccine coverage was higher in medical personnel than in the rest of professional categories.
  
  
  CONCLUSIONS
  There was a variable percentage of influenza AH1N1v seropositive individuals who had not suffered clinical symptomatology. This serological study detects differences on vaccine efficacy.
authors.affiliation: Unidad de Medicina Interna, Hospital Costa del Sol, Carretera Nacional 340, Marbella. julio.olalla@gmail.com
authors.forename: Julián
authors.initials: J
authors.lastname: Olalla Sierra
authors.forename: Fernando de
authors.initials: Fd
authors.lastname: Ory Manchón
authors.forename: Inmaculada
authors.initials: I
authors.lastname: Casas Flecha
authors.forename: Natalia
authors.initials: N
authors.lastname: Montiel Quezel-Guerraz
authors.forename: Daniel
authors.initials: D
authors.lastname: Salas Bravo
mesh_terms: D058345:Asymptomatic Infections / Q000453:epidemiology*; D006282:Health Personnel; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000453:epidemiology*; D015995:Prevalence; D011446:Prospective Studies