DEAR DR. DONOHUE: I have some questions about flu that I can’t find the answers to. I wonder if you’d be kind enough to tell me the information. How can you tell the difference between the flu and a cold? If you do get a flu shot, how long does it take before it protects you? If you don’t get a shot, what can you take in its place? How long can a person with the flu spread it, and how is it spread? How does a doctor know if you have the flu? — R.R. A: The difference between influenza — the flu — and a cold is great. Flu symptoms strike quickly. A cold comes on gradually. With the flu, people develop temperatures of 103 to 104 F (39.4 to 40 C). Such high temperatures are not seen with a cold. Symptoms of the flu include sore throat and runny nose — both common to a cold — but a bad headache, a dry hacking cough and muscle and joint pain are distinctly flu symptoms.

After a flu shot, it takes two weeks for the body to develop antibodies for protection against infection.

Relenza (zanamivir), administered in a spray, and Tamiflu (oseltamivir), a pill, can prevent flu as well as treat it.

An infected person spreads flu virus from the day before developing symptoms to five to 10 days after coming down with them. Flu virus is spread in airborne droplets from sneezing or coughing. It is a highly contagious infection. In a typical year, about one in 10 Canadians and Americans come down with the flu.

During an outbreak, doctors easily can diagnose flu from a patient’s symptoms. If need be, there are lab tests, even doctor’s office tests, that can fairly reliably provide confirmation that the flu virus is responsible for a person’s symptoms.

c. North America Syndicate