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.

ANSWER: 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.

DEAR DR. DONOHUE: A friend was taken by ambulance to the hospital because she suffered from vomiting and diarrhea. The diagnosis was cryptosporidium, a cousin of the E. coli bacterium. She almost died. She is a cancer patient with an impaired immune system. How does one become afflicted with this deadly disease? – W.B.

ANSWER: Cryptosporidium (KRIP-toe-spore-ID-ee-um) isn’t a bacterium. It’s a one-celled organism like an amoeba. About 300,000 people are infected with it yearly in the United States. It didn’t really hit the news until the AIDS epidemic struck. Cryptosporidium is a serious illness mostly for those whose immune system has been weakened, as it is in AIDS. It causes watery diarrhea that lasts for long periods and leads to dehydration that requires hospitalization. In people with a healthy immune system, it causes a self-limited diarrhea.

The illness is transmitted through contaminated water. In 1993, in Milwaukee, Wis., the city’s water was polluted with it, and the subsequent outbreak affected more than 400,000 people.

You shouldn’t have bad dreams about this illness. Humans have lived with it for a very long time. It doesn’t represent a deadly threat to most.

DEAR DR. DONOHUE: I have an issue I hope you can correct. I am a retired medical oncologist and a believer in mainstream nutrition recommendations. Sometimes getting in five servings of vegetables and fruits is difficult for people. While flying, at no cost (as yet), one can get a can of tomato juice, which is a vegetable serving as well as being a decent source of lycopene. Unfortunately, it also provides a large sodium load. There is a great alternative — namely, low-sodium V8, which is quite tasty. Is there any way to get the airline to act on this? – J.C., M.D.

ANSWER: Perhaps your letter will catch the attention of airline management, doctor.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from

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