DEAR DR. DONOHUE: My husband and I have a 2-year-old son who is in day care while we work. Last week he came down with what we thought was a bad cold. We were concerned, so my husband took him to the pediatrician, who made a diagnosis of fifth disease. When the doctor learned that he went to day care, he asked if any of the help was pregnant. We called, and one of the workers is. Our doctor told this woman to consult her doctor right away. Why? — V.O.

ANSWER: Fifth disease, also known as erythema infectiosum, is a viral illness that’s common in childhood. It leads to fever, fretfulness, muscle pain, sometimes vomiting and sometimes diarrhea. Anywhere from two to five days from the beginning of symptoms, the child’s cheeks turn bright red and look like someone has slapped them. From that point on, the child begins to feel well rapidly, and the rash fades quickly.

Most adults have had the illness as children, even if its signs were never recognized. A pregnant woman who never had the illness but comes down with it during pregnancy faces the possibility of suffering a miscarriage. Pregnant women who had the illness in the past are not at any risk of losing the fetus.

Pregnant women uncertain of their past exposure to the virus need to be tested by their doctor to see if they are newly infected. If they are, they do have a small risk of losing their baby.

No medicine is effective against this virus. Seldom are symptoms so severe that the child needs any treatment. In some instances, where the mother is infected for the first time during pregnancy, measures can be taken to treat the fetus if complications arise.

In all probability, the young woman at the day-care center will not suffer any consequences from exposure to your son.

DEAR DR. DONOHUE: My left knee is going to be replaced. It’s in bad shape. The surgeon has the operation scheduled. I told him I have peripheral artery disease in that leg. Is this consideration a contraindication for such an operation? My doctor is somewhat of a cowboy, if you know what I mean. — B.N.

ANSWER: Peripheral artery disease is a common affliction at older ages. It indicates that circulation in the leg is poor due to buildup of plaque — a mix of cholesterol, triglycerides, white blood cells and proteins, all clinging to artery walls. It’s the exact situation that happens to heart arteries to cause a heart attack and to brain arteries, where it causes a stroke.

Even though your circulation is poor, in most cases, a knee replacement can be done successfully.

If circulation is so bad that amputation is a distinct possibility in the near future, such surgery would not be attempted. No orthopedic surgeon, even a cowboy one, would consider replacing a knee in those circumstances.

DEAR DR. DONOHUE: Every now and then, my eyelid twitches. I don’t think it’s due to me being tired, because it can happen when I am wide awake in the morning. And I don’t think it’s due to stress — I love my work. Furthermore, I don’t drink any caffeinated beverages. What do you think is the significance of this? — H.R.

ANSWER: Nearly everyone has had a twitchy eyelid at some time in life. It’s not a sign of illness. It’s not something that lasts for any length of time. Fatigue, stress and caffeinated beverages all have been implicated as causes. But most people with a twitchy lid are like you; they have and do none of these things.

A washcloth soaked in warm water and placed on the involved, closed lid for a few minutes generally can stop the twitching. Or gentle massage of the involved, closed lid also can end it.

If it continues and lasts for longer periods, then a doctor has to be consulted.

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.