1. United Nations World Tourism Organization. World Tourism Barometer January 2012;10:1–6. Available at: http://mkt.unwto.org/en/barometer/january-2012-advance-release. Accessed November 30, 2012.
2. United Nations World Tourism Organization. World Tourism Barometer November 2012;10:1–8. Available at: http://mkt.unwto.org/en/barometer/november-2012-volume-10. Accessed November 30, 2012.
3. Office of Travel and Tourism Industries, International Trade Administration, U.S. Department of Commerce. 2011 United States Resident Travel Abroad. Available at: http://www.tinet.ita.doc.gov/outreachpages/download_data_table/2011_US_Travel_Abroad.pdf. Accessed November 18, 2012.
4. Office of Travel and Tourism Industries, International Trade Administration, U.S. Department of Commerce. Profile of U.S. resident travelers visiting overseas destinations: 2011 outbound. Available at: http://tinet.ita.doc.gov/outreachpages/download_data_table/2011_Outbound_Profile.pdf. Accessed November 18, 2012.
5. Health problems after travel to developing countries;Steffen;J Infect Dis,1987