FAMILY MEDICINE® COLUMN
By John C. Wolf, D.O.
Associate Professor of Family Medicine®
Ohio University College of Osteopathic Medicine

[TUBERCULOSIS TESTS DON'T PROTECT YOU FROM THE DISEASE]

Question: A person at work was sick, and her doctor thought she had tuberculosis. One of my co-workers said that he didn't have to worry about catching TB because he had a TB test and it gave him immunity to the disease. I thought TB tests just showed if you had been exposed to the disease and offered no protection from it. Obviously one of us is misinformed. Which one?

Answer: Tuberculosis is a common disease that is often referred to by the initials TB. The World Health Organization estimates that one third of the world's population is infected with this disease. Wow! Worldwide there are 8 million new cases each year and 2.9 million deaths.

This serious infection occurs in all parts of the world, especially in under-developed nations. It is less common in countries with abundant economic resources and effective public health systems. Our country falls into this fortunate second category. There are about 20,000 cases reported here each year. This is a much lower rate of infection than in Central America, Africa and Southeast Asia. Obviously, our public health efforts make a difference.

Tuberculosis is spread from one infected individual to another by a rather simple method. The infected person has the Tuberculosis bacteria in their lungs. When they cough, they send out a microscopic spray of these potentially lethal organisms into the air. The person who sits at their desk down the hall at the other end of the ventilator shaft, or the person standing beside him or her, inhales the bacteria. That unwitting soul has now been exposed to TB.

The bacteria grow slowly, so an infection is usually not apparent until weeks after the initial exposure. Most people develop a mild respiratory infection that finally clears up, although in some individuals it can progress to a life-threatening illness. For most people though, the body's immune system contains the infection without them knowing that the mild illness was actually caused by TB.

The TB skin test is done to determine if you have been exposed to this infection and subsequently had an immune system response to it. This test is positive in about 80 percent of those who either have an active case of TB or have developed immunity to the bacteria. By inference, you have probably already correctly assumed that there are about 20 percent of individuals with active TB who have a negative test.

Now to specifically address your question: Having a TB test provides no protection against contracting tuberculosis. Vaccination with bacille Calmette-Guerin (BCG) reduces the severity of TB if you should be exposed to it, but this immunization isn't used in the United States. Perhaps your friend was confusing this with TB testing.

I'll bet you are wondering if you should have a TB test. You definitely should if you work with a wide variety of people. Health-care professionals, teachers, bus drivers, etc. are good examples of those who should have a TB test every year or two. This is particularly true if you work with or are yourself an illicit drug user, have HIV or AIDS, or live in the inner city. Individuals in these groups have a much higher incidence of TB. Also, you should have a TB test if you have recently come from a part of the world where this disease is common. See your family doctor or health department if you have any additional questions about TB.

Family Medicine® is a weekly column. To submit questions, write to John C. Wolf, D.O., Ohio University College of Osteopathic Medicine, Grosvenor Hall, Athens, Ohio 45701.