Influenza (flu) is a viral infection. People often use the term "flu" to describe any kind of mild illness, such as a cold or a stomach virus, that has symptoms like the flu. But the real flu is different. Flu symptoms are usually worse than a cold and last longer. The flu usually does not cause vomiting or diarrhea in adults.
Most flu outbreaks happen in late fall and winter. Because symptoms may not start for a couple of days, you may pass the flu to someone before you know you have it.
The flu is caused by influenza viruses A and B. There are different strains of the flu virus every year.
The flu causes a fever, body aches, a headache, a dry cough, and a sore or dry throat. You will probably feel tired and less hungry than usual. The symptoms usually are the worst for the first 3 or 4 days. But it can take 1 to 2 weeks to get completely better.
It usually takes 1 to 4 days to get symptoms of the flu after you have been around someone who has the virus.
Most people get better without problems. But sometimes the flu can lead to a bacterial infection, such as an ear infection, a sinus infection, or bronchitis. Less often, the flu may cause a more serious problem, such as pneumonia.
Certain people are at higher risk of problems from the flu. They include young children, pregnant women, older adults, and people with long-term illnesses or with impaired immune systems that make it hard to fight infection.
Your doctor will ask you about your symptoms and examine you. This usually gives the doctor enough information to find out if you have the flu, especially if many cases of a similar illness have occurred in the area and the local health department reports a flu outbreak.
In some cases, the doctor may do a blood test or take a sample of fluid from your nose or throat to find out what type of flu virus you have.