CDC influenza information*:www.cdc.gov/ncidod/diseases/flu/weekly.htm,www.cdc.gov/ncidod/diseases/flu/fluvirus.htm

National Institute of Allergy and Infectious Diseases:www.niaid.nih.gov

World Health Organization:www.who.int/health-topics/influenza.htm

U.S. Department of Health and Human Services:www.dhhs.gov

American Lung Association:www.lungusa.org/diseases/luninfluenz.html

National Foundation for Infectious Disease:www.nfid.org/factsheets/inflfacts.html

Consumer health information from sources such as Aetna InteliHealth, featuring information from Harvard Medical School:www.intelihealth.com