Dear Dr. Donohue • My son had blood work done for employment at a hospital. He tested positive for latent TB, so now he has to take isoniazid for nine months. Is this a normal treatment for this kind of infection? What is the prognosis once he is done?

He is working with the Centers for Disease Control and Prevention on this, so we hope they know what they are doing. —J.T.

Answer • Latent TB indicates that a TB germ resides in the body, usually the lungs, and that it has gone into hibernation. Later in life, it can waken from its sleep, generate new TB germs and set off an active case of tuberculosis. Close to 80 percent of adult TB is due to this kind of reactivation.

Your son does not have TB, and he's not contagious. He does need treatment to eliminate the possibility that the germ will spring to life in the future. The chances of that happening range from 1 percent to 13 percent — not extremely high, but high enough to pose a threat to him and to others. An epidemic isn't going on because we have effective treatments for TB, active and latent.

The TB blood test is a new test that is better at detecting infection, both active and latent, gives quicker results and doesn't require the tested person to return to the doctor to interpret the test. Both the skin test and the blood test are still used, but the blood test is becoming more popular in places where it can be used.

Standard treatment for latent TB is nine months of isoniazid treatment. Recently, in December 2011, the CDC introduced an alternate regimen for latent TB, consisting of three months of weekly treatment of isoniazid with rifapentine. Your son will do fine on the treatment he started with. He doesn't have to change horses midstream.

Dear Dr. Donohue • I have a habit of talking to myself when I am alone. I've done this for some time. When I had my dog, it seemed OK, because she would look at me as though she understood the conversation. Last Christmas my sister visited and said she was concerned about this habit. Now she has me concerned. Am I in the beginning stages of Alzheimer's?

I live alone and take care of myself and the house without outside help. I drive, do all my shopping and cooking. I have many hobbies. — L.M.

Answer • Talking to oneself isn't a sign of Alzheimer's disease. It's not usually a sign of mental illness, unless there are other signs that the brain isn't functioning normally. Your brain is working well. You take care of yourself and your house. You keep occupied with many hobbies. It all sounds normal to me. I often talk to myself. I'm the only one I talk to who doesn't give me an argument.

Write Dr. Donohue at P.O. Box 536475, Orlando, Fla. 32853-6475.