DEAR DR. DONOHUE: Recently I heard that a number of people died from eating cantaloupe that had a bacterium called listeria. What causes it, and how did it originate? I have been growing vegetables all my life and never heard of it. Does it live just on the outside of fruits and vegetables, or does it get inside? Are there signs that listeria is on the ground or on foods? Does cooking kill it? — W.H.

ANSWER: Listeria is not a new bacterium. It’s been around on this planet a lot longer than any of us current humans have been. It’s found in soil, decaying vegetation, rivers, streams, lakes and in the digestive tracts of many animals and their feces. Many of us have been infected with it, but most often symptoms are so mild that they go unreported and untreated. Only on a relatively few occasions has listeria been a threat to life and health. The recent cantaloupe episode was one of those occasions.

This bacterium does not penetrate into the interior of fruits or vegetables. It’s on the cantaloupe rind. Cutting the fruit with a knife permits bacteria to cling to the knife and be deposited inside the melon, on the edible part. All fruits and vegetables should be washed thoroughly before they’re eaten.

Meats, chicken and seafood also can harbor listeria. They should all be well-cooked; cooking kills the germ. Unpasteurized milk is another food capable of transmitting it. It is not transferred from one human to another. An infected mother can pass the germ to her fetus.

People who are quite susceptible to infection with listeria are ones whose immune system is not as robust as it should be. Older individuals and newborns are at greater risk of becoming infected than are others. For people with healthy immune systems, the chief signs of infection are nausea, vomiting and diarrhea. Many never develop any signs. Heavy infections with great numbers of listeria cause a much more severe illness and can be fatal. Those examples actually are quite rare in comparison to the total number of infections.

You cannot tell if a food or if soil has listeria by sight alone.

DEAR DR. DONOHUE: I am 68 and have the average health issues. I truly lucked out. After a broken brain aneurysm, I came out fine.

I have begun to tire out fast and don’t know if it’s from being on Coumadin. A family member suggested postpolio syndrome. I asked the doctor about it, but all I get is, “Once you’ve had polio, you don’t get it again.” I had polio that affected my legs before the vaccine came out. Now my legs tire fast and hurt. I know age doesn’t help, so I get a pat on the head and sent home. Could my current symptoms be postpolio syndrome? — K.P.

ANSWER: Yes, they could. In fact they’re strongly suggestive of it.

Your new fatigue, leg tiring and leg pain likely are not due to being on Coumadin or due to your ruptured aneurysm of years ago. Nor are they likely to be age-related.

Postpolio syndrome seems a good bet. Twenty to 40 years after a polio attack, a person often notices weakness in the muscles that were originally involved in the infection. Those muscles improved after the attack because nearby nerve cells took over the work of nerves killed by the polio virus. Now those nerves that were doing double duty are giving out. That leads to new muscle weakness and new muscle pain. Overall fatigue is another prominent symptom of postpolio syndrome.

You need a neurologist’s opinion. I believe the family member was correct in suggesting postpolio syndrome.

DEAR DR. DONOHUE: On TV, I heard a doctor sing the importance of vitamin A. He also cautioned about the overuse of vitamin supplements. I don’t know how valid studies on vitamins are, but they eventually become obsolete with the newest research. There is no way to know the quality of research. I no longer pay any attention to the information on food labels. I will be 91 in a few months. — R.D.

ANSWER: I always pay attention to what 90-year-olds say. They must’ve done things right, or they wouldn’t be here. I agree with you. Nutritional advice changes so rapidly and so radically that it is hard to evaluate it. I guess we have to judge what makes the best sense.

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 www.rbmamall.com.