Influenza, also known as the flu, is a contagious respiratory disease caused by different strains of viruses. In the United States, there is a flu season that begins every fall and ends every spring. The type of flu people get during this season is called seasonal flu. Flu viruses spread from person to person when people who are infected cough or sneeze. Know the DifferenceSeasonal Flu—A contagious respiratory illness caused by influenza (flu) viruses occurring every year. It affects an average of 5 percent to 20 percent of the U.S. population by causing mild to severe illness, and in some instances can lead to death. Adults may be able to infect others 1 day before getting symptoms and as long as 5 days after getting sick. Epidemic—The rapid spread of a disease that affects some or many people in a community or region at the same time. Pandemic—An outbreak of a disease that affects large numbers of people throughout the world and spreads rapidly. H1N1 Influenza (swine flu)—H1N1, referred to as “swine flu” early on, is a new influenza virus causing illness in people. In the United States, this new virus was first detected in people in April 2009. This virus is spreading from person-to-person worldwide, probably in much the same way that regular seasonal influenza viruses spread. On June 11, 2009 the World Health Organization (WHO) signaled that a pandemic of H1N1 was underway. It is important to stay informed about changes to guidance issued by the Centers for Disease Control and Prevention (CDC). The CDC Web site posts regular updates to public health recommendations regarding a number of public health threats, including H1N1 (swine flu). H5N1 (avian flu)—Commonly known as bird flu, this strain of influenza virus is naturally occurring in birds. Wild birds can carry the virus and may not get sick from it; however, domestic birds may become infected by the virus and often die from it. What should I do to avoid getting sick? Get your flu shot every year for the best chance of protection. Do I have the flu? The flu usually begins with the rapid onset of a high fever and body aches. Be aware of other common flu symptoms:Diagnosing the fluPotential risks and serious complications of the flu:What should I do when someone is sick? Designate one person as the caregiver. Keep everyone’s personal items separate. All household members should avoid sharing pens, papers, clothes, towels, sheets, blankets, food or eating utensils unless they have been cleaned between uses. Disinfect doorknobs, switches, handles, computers, telephones, toys and other surfaces that are commonly touched around the home or workplace. Wash everyone’s dishes in the dishwasher or by hand using very hot water and soap. Wash everyone’s clothes in a standard washing machine as you normally would. Use detergent and very hot water and wash your hands after handling dirty laundry. Wear disposable gloves when in contact with or cleaning up body fluids. Immunity to a disease is defined by the presence of antibodies to that disease in a person’s system. Most people have some resistance to infections, either after they recover from an illness or through vaccination. Seasonal flu viruses change over time and immunity to them cannot be acquired unless vaccination is administered. Quarantine is the physical separation of healthy people who have been exposed to an infectious disease from those who have not been exposed. Isolation is a state of separation between persons or groups to prevent the spread of disease. Social distancing is a practice imposed to limit face-to-face interaction in order to prevent exposure and transmission of a disease.