Understanding Influenza

What Causes Influenza?

Influenza (flu), also referred to as seasonal flu, is a highly contagious illness caused by the influenza virus. Anyone can get the flu as it is spread easily from person to person, usually when an infected person coughs or sneezes. 

Types of Influenza

The virus may belong to one of three different influenza virus fami­lies: A, B or C.  

Influenza type A viruses can infect people, as well as birds, pigs, horses, and other animals. Influenza A viruses can be further broken down into different strains. There are two subtypes of influenza A viruses found in and circulating among humans: regular H1N1 and H3N2. These two subtypes are included in the seasonal flu vaccine each year. The novel H1N1 influenza virus, also known as swine flu, is a subtype of influenza type A. It was first seen widespread throughout the world in 2009. It causes illness similar to seasonal flu. Protection against this flu virus is now contained in the seasonal influenza vaccine.

Influenza Type B viruses are usually found only in humans. Influenza B viruses can cause illness among humans, but in general are associated with less severe contagious disease than influenza A viruses.

Influenza Type C viruses cause mild illness in humans. Influenza C cases occur much less frequently than A and B and are not typically included in the seasonal flu vaccine.

In addition to seasonal flu, there is another type of flu virus:

Avian flu (H5N1):  Avian influenza, or bird flu, is also a subtype of influenza type A viruses. While highly contagious in birds, it does not usually infect humans. Most cases of human infection with bird flu viruses have occurred in Asia, parts of Europe, the Near East, the Pacific and Africa. The virus is mainly transmitted to humans by direct contact with infected live, sick or dead poultry. However, it is thought that a few cases of human-to-human spread have occurred.

Are You at Risk for Getting the Flu?

Each year around 3,000 to 49,000 Americans die from flu and its complications. For healthy children and adults, influenza is typically a moderately severe illness. Most people are back on their feet within a week. Certain groups of people are more susceptible to complications related to the flu and are considered "high risk." These groups include the elderly, very young children and people with chronic illnesses or compromised immune systems. For people who are not healthy to begin with, influenza can be very severe and even fatal. If you are considered "high risk," you should do everything you can to prevent the flu.

What Should I Do if I Get the Flu?

Anyone concerned about their illness should consult a healthcare provider. The best thing to do is to stay home and avoid contact with other people except to get medical care. If you are considered high risk, it is important to contact your healthcare provider right away. People at high risk are more likely to suffer from severe complications from the influenza virus. Pneumonia is the most common serious complication of influenza.