An old bacterium causes new fear

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 • 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. 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.