Influenza virus infection in travelers to tropical and subtropical countries

Clin Infect Dis. 2005 May 1;40(9):1282-7. doi: 10.1086/429243. Epub 2005 Mar 28.


Background: Influenza outbreaks have been reported among travelers, but attack rates and incidence are unknown.

Methods: A cohort study was conducted. Travelers to subtropical and tropical countries recruited at the University of Zurich Travel Clinic (Switzerland), January 1998 to March 2000, were investigated with pre- and posttravel assessment of hemagglutination inhibition and by questionnaire.

Results: Among 1450 travelers recruited who completed questionnaires and provided serum samples before departure, 289 (19.9%) reported febrile illness during or after traveling abroad; of these, 211 (73.0%) provided paired serum samples. Additionally, paired serum samples were collected from 321 frequency-matched afebrile control subjects among the remaining 1161 subjects of the study population. Seroconversion for influenza virus infection was demonstrated in 40 (2.8%) of all travelers; 18 participants (1.2%) had a > or = 4-fold increase in antibody titers. This corresponds to an incidence of 1.0 influenza-associated events per 100 person-months abroad. Among the 211 febrile participants, 27 (12.8%) had seroconversion, 13 (6.2%) with a > or = 4-fold increase; among the 321 afebrile control subjects, 13 (4.0%) had seroconversion, 5 (1.6%) with a > or = 4-fold increase. Twenty-five seroconverters (62.5%; P = .747) acquired influenza outside of the European epidemic season. Sixteen patients (40.0%) sought medical attention either abroad or at home, and 32 (80.0%) were asymptomatic at the time of completion of the survey.

Conclusions: This survey indicates that influenza is the most frequent vaccine-preventable infection among travelers to subtropical and tropical countries. Infections occur mainly outside the domestic epidemic season, and they have a considerable impact. Pretravel vaccination should be considered for travelers to subtropical and tropical countries.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Child
  • Disease Outbreaks
  • Female
  • Health Surveys*
  • Humans
  • Incidence
  • Influenza, Human / epidemiology*
  • Male
  • Middle Aged
  • Odds Ratio
  • Risk Factors
  • Surveys and Questionnaires
  • Switzerland / epidemiology
  • Switzerland / ethnology
  • Time Factors
  • Travel*
  • Tropical Climate*