Latent vs. Active Tuberculosis

Q:  Please give us information on TB, or tuberculosis. We have been tutoring a family from Africa who came to this country two months ago. On arrival, we were told their medical check-ups were acceptable, but we have since learned that four of the eight family members are being treated for TB.

Should we be tested?

A:  Tuberculosis (TB) is a disease caused by bacteria called Mycobacterium tuberculosis. The bacteria usually attack the lungs, but TB bacteria can attack any part of the body such as the kidney, spine, and brain.

Latent TB Infection
TB bacteria sometimes manage to fool the immune system. With tuberculosis, the immune system can very quickly quiet the infection so that you have no symptoms and you are not contagious, but the "germ" is not completely eliminated from your body. This is called a "latent infection." People who have latent TB infection do not feel sick, do not have any symptoms, and cannot spread TB to others. But some people with latent TB infection go on to get TB disease.

The problem with tuberculosis is when the latent infection turns "active." In active TB, you may cough, feel lousy and lose weight over months. And you are contagious. Many people who have latent TB infection never develop active TB disease. In these people, the TB bacteria remain inactive for a lifetime without causing disease.

Active TB Disease
TB is spread through the air from one person to another. The bacteria are put into the air when a person with active TB disease of the lungs or throat coughs or sneezes. People nearby may breathe in these bacteria and become infected. People with active TB disease can be treated and cured if they seek medical help. Even better, people with latent TB infection can take medicine so that they will not develop active TB disease.

Some people develop active TB disease soon after becoming infected, before their immune system can fight the TB bacteria. Other people may get sick later, when their immune system becomes weak for another reason.

People with active TB disease are most likely to spread it to people they spend time with every day. This includes family members, friends, and coworkers. Symptoms of active TB disease include:

• weakness or fatigue
• weight loss
• no appetite
• chills
• fever
• sweating at night

The best way to prevent active TB is to treat latent TB with antibiotics. I imagine that is what is going on with the family members you tutor. In other words, they cannot pass the TB to you, but they are being treated to protect themselves from symptomatic infection. They likely became infected with TB in an endemic area of Africa, where 0.5% to 1% of all people have TB.

You can be tested for TB if you like. The TB test involves the injection of a TB-like substance just under the surface of the skin, using a very small needle. About two days later, the area is examined for a red, rash-like reaction. The Immigration and Naturalization Service requires all immigrants be tested for TB, and I'm sure that's how your African friends learned of their infection.

Julie L. Mitchell, MD, MS, is an Assistant Professor of Medicine at the Medical College of Wisconsin. She practices at the Froedtert & The Medical College of Wisconsin General Internal Medicine Clinic - East. Her column appears in the Milwaukee Journal-Sentinel.

This article includes information from the US Centers for Disease Control and Prevention.