title: The challenges of disease risk ascertainment using accessible data sources for numbers of travelers.
abstract: BACKGROUND
  Accessible travel has led to a rapid growth in international tourism, particularly to developing countries. With the increase, travel-associated morbidity and mortality has changed. Data on traveling populations are essential for policy makers to estimate infectious and noninfectious risks in travelers. Passenger flow statistics are compiled by the World Tourism Organization (WTO) and by official institutions of some countries. This study investigates sources of passenger flow statistics, methods of data collection, and compares datasets for consistency.
  
  
  METHODS
  Four national datasets of departing travelers were compared to the United Nations' World Tourism Organization (WTO) data on passenger arrivals to eight destination countries. The ratio between arrivals and departures was calculated (main destination ratio [MDR]) to estimate the proportion of direct to indirect traveler arrivals.
  
  
  RESULTS
  With few exceptions, arrival data exceeded that of departure data for all destinations. India is a primary destination for Australian residents where arrival and departure figures were similar (MDR 1.1), while visits to Cambodia and Turkey, with 3.6- and 3.8-fold higher arrivals, respectively, are part of multidestination trips. For UK residents, arrivals exceeded departures for all destinations except India where the reverse was true (MDR 0.8). A close correlation between arrivals and departures was noted for visits to South Africa while arrivals to Singapore and Cambodia were 7- and 10-fold higher, respectively. Arrivals by Finnish residents to destination countries were 1.4- to 1.6-fold higher than departures and 2.2-fold higher for Canadians visiting China.
  
  
  CONCLUSIONS
  Different methodologies used to capture arrival and departure statistics result in different estimations of traveler numbers. Data from a single source does not provide a comprehensive picture of most tourism itineraries. Inbound statistics give a more accurate reflection of the total visits made by travelers from a source country.
authors.affiliation: Hospital for Tropical Diseases, Mortimer Market Centre, London, UK; Department of Clinical Research, Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK.
authors.forename: Ronald H
authors.initials: RH
authors.lastname: Behrens
authors.forename: Bernadette
authors.initials: B
authors.lastname: Carroll
mesh_terms: D064870:Air Travel / Q000706:statistics & numerical data / Q000639:trends; D021821:Communicable Diseases, Emerging / Q000453:epidemiology / Q000635:transmission; D003625:Data Collection; D014943:Global Health / Q000706:statistics & numerical data / Q000639:trends; D006801:Humans; D007391:International Cooperation; D009017:Morbidity / Q000639:trends; D009026:Mortality / Q000639:trends; D018570:Risk Assessment; D012307:Risk Factors; D014186:Transportation / Q000379:methods / Q000706:statistics & numerical data; D006113:United Kingdom / Q000453:epidemiology