1. International Trade Administration, U.S. Department of Commerce. 2013 United States Resident Travel Abroad. 2013. http://travel.trade.gov/outreachpages/download_data_table/2013_US_Travel_Abroad.pdf (5 January 2015, date last accessed).
2. International Trade Administration, U.S. Department of Commerce. Top Destinations for U.S. Travelers 1995/1994. 1994. http://travel.trade.gov/view/f-3/freeab23.html (5 January 2015, date last accessed).
3. Non-pneumococcal mitis-group streptococci confound detection of pneumococcal capsular serotype-specific loci in upper respiratory tract
4. National Center for Immunization and Resiratory Diseases, Division of Viral Diseases, Centers for Disease Control and Prevention. U.S. Multi-state Measles Outbreak 2014—2015. 2015. http://www.cdc.gov/measles/multi-state-outbreak.html (18 March 2015, date last accessed).
5. Prevention of travel-related infectious diseases: Knowledge, practices and attitudes of Swedish travellers