Understanding Tuberculosis - the Basics

What Is Tuberculosis?

Tuberculosis, commonly known as TB, is a bacterial infection that can spread through the lymph nodes and bloodstream to any organ in your body -- and most often is found in the lungs. Most people who are exposed to TB never develop symptoms, since the bacteria can live in an inactive form in the body. But if the immune system weakens, such as in people with HIV or elderly adults, TB bacteria can become active. In their active state, TB bacteria cause death of tissue in the organs they infect. Active TB disease can be fatal if left untreated.

Because the bacteria that cause tuberculosis are transmitted through the air, the disease can be quite contagious. But it's nearly impossible to catch TB by a single, social contact with an infected person. To be at risk of being infected, you must be exposed to TB bacteria constantly, by living or working in close quarters with someone who has the active disease. Even then, because the bacteria generally stay latent (inactive) after they invade the body, only 10% of people infected with TB will ever have the active disease. The remaining 90% have what's called latent TB infection -- they show no signs of infection and won't be able to spread the disease to others.

These latent infections can eventually become active, though, so even people without symptoms should receive medical treatment. Medication can help get rid of the inactive bacteria before they become active.

• What’s it like to be diagnosed with tuberculosis? Read one woman’s story.

Once a widespread disease, TB became relatively rare with the help of antibiotics developed in the 1950s. Two decades ago, the U.S. Surgeon General announced that tuberculosis was a disease of the past. He spoke too soon: The disease has since resurfaced in a potent new form called multidrug-resistant TB. Today, this new and dangerous form of TB -- resistant to some of the commonly used drug treatments -- has created a public health crisis in many large cities worldwide. If you have TB -- in its active or dormant state -- you must seek medical treatment.

What Causes It?

Because the bacteria that cause tuberculosis are transmitted through the air, the disease can be quite contagious. But it's nearly impossible to catch TB by a single, social contact with an infected person. To be at risk of being infected, you must be exposed to TB bacteria more intensely, by living or working in close quarters with someone who has the active disease. Even then, because the bacteria generally stay latent (inactive) after they invade the body, only 10% of people infected with TB will ever have the active disease. The remaining 90% have what's called latent TB infection -- they show no signs of infection and won't be able to spread the disease to others.

These latent infections can eventually become active, though, so even people without symptoms should receive medical treatment. Medication can help get rid of the inactive bacteria before they become active.