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In understanding TB, it’s important to understand the difference between Mtb infection and TB disease.

Mtb Infection

Health experts estimate that more than one-third of the world’s population has the TB bacterium in their bodies, which means they have Mtb infection. In addition, new infections are occurring at the rate of one per second. Fortunately, only a fraction of people infected with Mtb develops active TB disease. Those who do not get sick are known to have non-contagious latent TB, so-called because the bacteria are inactive or “asleep” in the body.

TB bacteria can remain in this dormant state for months, years, and even decades without increasing in number and without making the person sick. Most people with latent Mtb infection will test positive on the tuberculin skin test, or their chest X-ray will show signs of latent TB. These findings indicate that they have TB bacteria in their bodies, but most infected people will not develop active TB disease, may never get sick, may never show any symptoms, and may never spread the bacteria to others.

However, one in ten people infected with TB bacteria, do develop active TB disease. Therefore, it is important to get the appropriate treatment and get rid of the bacteria in both latent TB and active TB disease.

TB Disease

People with weakened immune systems (those with HIV/AIDS, those receiving chemotherapy, or children under 5 years old, for example) are at a greater risk for developing TB disease. When they breathe in TB bacteria, the bacteria settle in their lungs and start growing because their immune systems cannot fight the bacteria. In these people, TB disease may develop within days or weeks after the infection. However, in some other people, TB disease may develop months or years after the initial infection, at a time when the immune system becomes weak for other reasons and is no longer able to fight the bacteria.

When a person gets active TB, it means TB bacteria are multiplying and attacking the lung(s) or other parts of the body, such as the lymph nodes, bones, kidney, brain, spine, and even the skin. From the lungs, TB bacteria move through the blood to different parts of the body. Symptoms of active disease include cough, loss of weight and appetite, fever, chills and night sweats as well as symptoms from the specific organ or system that is affected; for example, coughing up blood or sputum in TB of the lungs, or bone pain if the bacteria have invaded the bones.

TB disease usually can be cured with prompt and appropriate treatment, but it remains a major cause of death and disability in the world, particularly among people infected with HIV.

TB Bacteria Are Spread Only From a Person With Active TB Disease

In people who develop active TB of the lungs, also called pulmonary TB, the TB skin test will often be positive. In addition, they will show all the signs and symptoms of TB disease and can pass the bacteria to others. So, if a person with TB of the lungs sneezes, coughs, talks, sings, or does anything that forces the bacteria into the air, other people nearby may breathe in TB bacteria. Statistics show that approximately one-third of people exposed to pulmonary TB become infected with the bacteria, but only one in ten of these infected people develop active TB disease during their lifetimes.

Among people suffering from TB disease, three out of four have disease affecting the lungs. If not treated immediately, the bacteria have the potential to destroy the lungs and kill the person.