Latent tuberculosis can turn active at any time

Discussing test results

Dear Doctors: I am 14 years old and recently had to test for tuberculosis. What is the common age range for tuberculosis? I did some research and learned that there are both latent and active tuberculosis infections. What is the cause of this dormant phase in tuberculosis bacteria?

Dear Reader: Tuberculosis is a serious infectious disease caused by bacteria that can affect anyone at any age. Although it usually infects the lungs, the bacteria can travel via the blood to other parts of the body. This includes the spine, lymph nodes, kidneys and brain.

Here in the United States, most cases of tuberculosis, or TB, are caused by Mycobacterium tuberculosis. It spreads through the air on minute droplets that someone with an active lung infection emits when they sneeze, cough, shout or sing. To become infected, you must be close enough to inhale the bacteria-laden droplets.

Not everyone infected with TB bacteria gets sick. As you point out, this is known as a latent infection. It means that although the bacterium is present in the body, it is not actively growing or reproducing, and, thus, not causing symptoms. That’s because the immune system has identified the bacteria as a threat and successfully isolated it. It is estimated that as few as 10% of people infected with TB bacteria go on to develop the active form of tuberculosis. However -- and this is why testing is important -- it is possible for the bacteria to become active at any time. The shift can occur when additional burdens on the immune system -- such as illness, extreme stress or immunosuppressive treatment for another condition -- allow the bacteria to grow and multiply.

Active disease can occur anywhere from a few weeks to many years after an initial infection. Infants, young children, older adults and people living with weakened or suppressed immune function are at highest risk. Symptoms include a persistent cough not associated with a viral infection, weakness, fatigue, chest pain, shortness of breath, loss of appetite, chills, night sweats, unintended weight loss, fever and bloody sputum.

Diagnosis for TB begins with a skin-prick test. If those results are positive, blood tests and chest X-rays are used to confirm the diagnosis and to determine if the infection is active or latent.

Both latent and active forms of TB are treated with antibiotics. For latent infections, treatment can last from three to six months. Active infection requires a longer course of treatment, often with two drugs. Unfortunately, some forms of the TB bacteria have become drug-resistant, even to combinations of drugs. This has led to the development of tests to identify genetic mutations in TB bacteria. Those results are used to choose drug combinations with the best chance of outwitting the mutated bacteria.

Active tuberculosis is a potentially fatal disease. It can cause permanent damage to the lungs, and can also spread to other parts of the body, causing serious health complications, including organ damage. Tuberculosis causes millions of deaths worldwide each year. That makes it very important for anyone with a TB diagnosis to follow through with treatment.

(Send your questions to [email protected], or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

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