DEAR DR. DONOHUE: My baby, who is 10 months old, came down with a horrible case of diarrhea. He was so sick, he had to be hospitalized and given intravenous fluids. It turns out he had a rotavirus infection. I have another child, 13. Can that boy, my husband or I come down with this too? – T.R.

ANSWER: Rotavirus has infected nearly all children by the time they reach their 5th birthday. It’s transmitted to others in a number of ways – the hands of the infected, contaminated food or drink and from surfaces touched by an infected infant or adult. Fall and winter are the peak rotavirus seasons.

Adults and older children can get the infection, but they come down with less severe symptoms. A sick infant can pass the virus up to the eighth day after becoming ill. If you or your family hasn’t come down with diarrhea by the time you read this, it is unlikely that any of you will.

Infant infection generally starts abruptly with vomiting. Then the loose stools begin. About one-third of affected infants have a temperature of 102°F (39°C). The danger of a rotavirus infection is dehydration, which can occur rapidly.

If the baby can tolerate oral fluids, then one of the numerous infant rehydration fluids, like Pedialyte, can usually take care of matters at home.

However, some babies must be hospitalized for rehydration with intravenous fluids. About 50,000 North American infants are hospitalized every year because of rotavirus infection, and around 20 babies die from it. Since this is a viral infection, antibiotics are ineffective treatments. The illness runs its own course usually in a week or so.

There was a vaccine on the market for this infection. It was withdrawn because it appeared to be associated with intussusception, a condition where one part of the intestine is drawn into an adjacent segment. Intussusception carries a high mortality rate.

DEAR DR. DONOHUE: My husband was rewiring our house and spent hours on his knees in our attic. The following day he complained of a sore left knee. The day after that, the knee was red and swollen. I took him to the ER, where they made a diagnosis of cellulitis. Then it turned into bursitis, and a surgeon had to open up the infection to drain. He was given antibiotics by vein. How did he get this? – R.V.

ANSWER: Cellulitis is an infection of skin cells and the cells and tissues beneath the skin. Undoubtedly a small object pricked your husband’s skin when he was on his knees. The skin nick can be so small that people never pay any attention to it. Bacteria rush through microscopic skin tears and bring on an infection that spreads rapidly. Staph or strep germs are the ones usually implicated in cellulitis.

Bursae are little pancake-shaped discs that reduce friction between bones and tendons. There are a number of them near the knee. From the skin to a knee bursa is not a great distance, and the bacteria can swim to the bursa destination quickly.

Drainage of infection encased in a bursa is essential for speedy healing.

The intravenous administration of antibiotics permits a rapid buildup of antibiotic blood concentration and provides a howitzer-sized bombardment of the invading bacteria.

DEAR DR. DONOHUE: I am 69 years old and have been treated for heart disease for five years. This past month it was discovered that I was not making enough thyroid hormone. I had felt dragged out for quite some time. The doctor put me on a low dose of thyroid hormone and says he’s going to increase it slowly. Why? I am tired of being tired. – O.B.

ANSWER: It’s standard practice to begin an older person with heart disease on a small dose of thyroid hormone in order to not stress the heart. Thyroid hormone perks up all body systems and is likely to cause a speedup of the heart. A full dose could be too much for the heart, so a period of gradual buildup is a safer way to restore the hormone level.

DEAR DR. DONOHUE: After many blood tests and biopsies, I was told I have dermatomyositis. Please give me some information on this condition. I am being treated with prednisone and methotrexate. – B.X.

ANSWER: The name “dermatomyositis” (DUR-muh-toe-MY-uh-SITE-us) says it all. It indicates that skin (“derm”) and muscles (“myo”) are inflamed (“itis”). For every man who has it, three women have it, and there are two age peaks when it usually strikes: 7 to 15 and 30 to 50.

The muscles of the shoulders and hips are often the first targets. People find it difficult to rise from a chair, climb stairs or comb their hair. The weakened muscles also hurt.

A lavender rash surrounding the upper eyelids is a common skin manifestation. The same-color rash can appear on the upper chest and shoulders. Sometimes a scaly, red eruption breaks out on the knuckles, knees, elbows and ankles.

Evidence points to an immune system attack on muscles and skin, but what prompts the attack remains an enigma.

Other organs – heart, lungs and digestive tract, either singly or in combination – can also be involved in the process.

A number of tests confirm the diagnosis. The blood level of muscle enzymes is quite high. Recording the electrical activity of muscles demonstrates their dysfunction. A muscle biopsy furnishes proof of muscle inflammation.

Prednisone, a cortisone drug, is usually the drug used to quiet inflammation. Often another drug, such as methotrexate, is added to the regimen to halt the immune attack. As the process comes under control, physical therapy is essential.

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.