title: Pandemic A/H1N1 influenza: transmission of the first cases in Spain.
abstract: BACKGROUND
  Pandemic A/H1N1 influenza emerged in Mexico at the end of March 2009. Since then, it is still important to provide evidences that contributed to the international spread of the virus and to ascertain the attack rate of this new strain of influenza among the first cases in Spain that led to identify the first transmission in Europe.
  
  
  METHODS
  Three pandemic A/H1N1 influenza groups related to an overseas flight were studied: 71 student group, 94 remaining passengers, and 68 contacts of confirmed cases. The attack rate with their 95% confidence interval (CI) among the student group and contacts was calculated. On April 26th, when the first cases were notified, strong preventive measures were implemented among the student group and the contacts of the confirmed cases.
  
  
  RESULTS
  On 27th April, the first pandemic A/H1N1 influenza cases confirmed in Spain were three students that came back from Mexico by airplane. A student generated the first native case in Spain and one of the first cases in Europe. Similar attack rates were found between the student group (14.1%; CI: 12.1-16.1) and their contacts (13.2%; CI: 4.4-22.0), but no cases among remaining passengers were detected, suggesting low transmission risk during air travel.
  
  
  CONCLUSIONS
  The first cases of pandemic A/H1N1 influenza in Spain were imported by airplane from Mexico. Preventive efforts to reduce the impact of the influenza influenced that primary and secondary rates were lower than first estimations by WHO.
authors.affiliation: Parc de Salut Mar-Universitat Pompeu Fabra-Public Health Agency of Barcelona, Spain. lcatala@aspb.es
authors.forename: Laura
authors.initials: L
authors.lastname: Català
authors.forename: Cristina
authors.initials: C
authors.lastname: Rius
authors.forename: Patricia
authors.initials: P
authors.lastname: García de Olalla
authors.forename: Jeanne L
authors.initials: JL
authors.lastname: Nelson
authors.forename: Josep
authors.initials: J
authors.lastname: Alvarez
authors.forename: Sofía
authors.initials: S
authors.lastname: Minguell
authors.forename: Neus
authors.initials: N
authors.lastname: Camps
authors.forename: María Rosa
authors.initials: MR
authors.lastname: Sala
authors.forename: Carlos
authors.initials: C
authors.lastname: Arias
authors.forename: Irene
authors.initials: I
authors.lastname: Barrabeig
authors.forename: Mónica
authors.initials: M
authors.lastname: Carol
authors.forename: Roser
authors.initials: R
authors.lastname: Torra
authors.forename: Neus
authors.initials: N
authors.lastname: Cardeñosa
authors.forename: Tomas
authors.initials: T
authors.lastname: Pumarola
authors.forename: Joan A
authors.initials: JA
authors.lastname: Caylà
mesh_terms: D000328:Adult; D000337:Aerospace Medicine; D000401:Aircraft; D016358:Contact Tracing; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control / Q000635:transmission / Q000821:virology; D008297:Male; D008800:Mexico; D058873:Pandemics; D012189:Retrospective Studies; D012919:Social Behavior; D013030:Spain / Q000453:epidemiology; D013334:Students; D014195:Travel; D055815:Young Adult