Q: What is the flu?

The flu is a respiratory infection caused by influenza virus. Viral particles are expelled into the air when an infected person coughs or sneezes. It takes from one to four days to develop symptoms after exposure to the virus.

Influenza viruses are broadly categorized into Type A or Type B, each of which encompasses multiple substrains. Type C flu is very mild and is not likely to cause dangerous epidemics.

Q: What are the symptoms? Do complications occur?

Symptoms are rapid onset of fever, chills, headache, cough, sore throat and extreme fatigue. Children could also have nausea, vomiting and diarrhea, but gastrointestinal symptoms are less common in adults.

Complications such as bacterial pneumonia, dehydration and worsening of conditions like heart failure, asthma and diabetes can occur. In children, the flu can lead to sinus and ear infections.

Q: Can infection be prevented?

In the spring, health authorities tell manufacturers which three strains should be in the vaccine, based on what was commonly seen overseas.

This season, the vaccine contains killed versions of Type A-Panama, Type A-New Caledonia and Type B-Hong Kong. Last month, the U.S. Centers for Disease Control and Prevention said several states were having outbreaks with Type A-Fujian. The Fujian and Panama strains are very similar, and the CDC says the vaccine will still offer protection.

Because vaccine takes many months to make, it is too late to make a new batch to specifically prevent infection with the Fujian strain.

Hand washing can slow the spread of flu as well as other infections.

Q: Who should get vaccinated?

Flu shots or a recently approved nasal preparation called FluMist can reduce the risk of infection and complications, so health authorities recommend that certain high-risk groups get the vaccine.

People of any age who have chronic medical conditions or are 50 and older are considered to be at high risk of complications. Studies indicate that healthy children 6 to 23 months old are more likely to need hospitalization when they get the flu, so they, too, should get vaccinated. Women who will be more than three months pregnant are also at greater risk for complications.

People who are not in a high-risk group can get the vaccine, but should expect to pay out of pocket for it.

Q: How can I tell if I have the flu?

It's difficult to distinguish between respiratory infections with influenza, common cold viruses or bacteria because the symptoms are similar. The only way to know for sure is to be tested by your doctor within a few days of getting sick.

Q: Where can I get vaccinated?

Your doctor may have vaccine available, either as a shot or as FluMist. The Allegheny County Health Department runs a flu shot clinic from Monday to Friday. More information, including other centers that offer vaccination, is avilable online at post-gazette.com