Influenza (flu) is a contagious respiratory illness caused by Influenza virus, most commonly type A or B. It can cause illness ranging from mild to severe. Serious outcomes of flu infection can result in hospitalization or death. Some people, such as older people, young children, pregnant women, people with compromised immune systems, people with asthma or other respiratory diseases, and other comorbidities, are at higher risk of serious flu complications.

Influenza A (H1N1), A (H3N2), and one or two influenza B viruses (depending on the vaccine) are included in each year’s influenza vaccine. Getting a flu vaccine can protect you against flu viruses that are the same or related to the viruses in the vaccine. Information about this season’s vaccine can be found at: https://www.cdc.gov/flu/protect/vaccine/index.htm.

Influenza is a seasonal virus and there are many other non-flu viruses that can result in influenza-like illness (ILI) that spread during flu season. Flu vaccines will NOT protect against infection and illness caused by other viruses that also can cause influenza-like symptoms.

Signs and symptoms of flu

People who have the flu often feel some or all of these signs and symptoms that usually start suddenly, not gradually:

■ Fever* or feeling feverish/chills

■ Cough

■ Sore throat

■ Runny or stuffy nose

■ Muscle or body aches

■ Headaches

■ Fatigue (very tired)

■ Some people may have vomiting and diarrhea, though this is more common in young children than in adults.

How flu spreads

Flu viruses are spread mainly by tiny droplets made when people with flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby. Less often, a person might also get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose, or possibly their eyes.

You may be able to pass on the flu to someone else before you know you are sick, as well as while you are sick. Although people with the flu are most contagious in the first three to four days after their illness begins, some otherwise healthy adults may be able to infect others beginning one day before symptoms develop and up to five to seven days after becoming sick. Some people, especially young children and people with weakened immune systems, might be able to infect others with flu viruses for an even longer time.

Preventing seasonal flu

■ The first and most important step in preventing flu is to get a flu vaccination each year. Typically, the Flu season is during the winter so getting the vaccination in fall or early winter is recommended as it takes several weeks for the vaccine to be most effective.

■ If you have symptoms cover your cough. Cough into a tissue or into your armpit if you don’t have a tissue. Wearing a mask can also prevent you from spreading the flu if you have symptoms.

■ Handwashing frequently is also a major mechanism to prevent spreading the flu.

■ CDC also recommends staying away from people who may have flu symptoms, or if you have symptoms to stay home unless you need medical attention.

Will my health care provider test me for flu if I have flu-like symptoms?

Not necessarily. Most people with flu symptoms are not tested because the test results usually do not change how you are treated. Your health care provider may diagnose you with flu based on your symptoms and their clinical judgment or they may choose to use an influenza diagnostic test.

Can the flu be treated?

Yes. If treatment is started within two days of becoming sick with flu symptoms, antiviral drugs can lessen symptoms and shorten the time you are sick by about one day. They may reduce the risk of complications such as ear infections in children, and pneumonia and hospitalizations in adults. If you have had symptoms for more than 48 hours the antiviral drug may not provide much benefit. Additionally, antibiotics do not have any impact on the flu virus.

What should I do if I think I have the flu?

Check with your doctor promptly if you are at high risk of serious flu complications and you develop flu symptoms.

Craig Jestila is the clinical quality director at Bay Area Medical Center.