An Overview of Tuberculosis (TB)

Tuberculosis (TB) is a contagious airborne disease caused by Mycobacterium tuberculosis, a bacterium that grows and divides inside of cells. The infection, which starts in the lungs, causes nodules known as tubercles, or Ghon focii, which are spots left by dead infected tissue. With time, the disease can spread to other areas of the lung and larger areas of lung tissue may die off, causing cavities. Bacteria can also spread to other organs, including the kidney, brain, and spine.

Antibiotics are used for tuberculosis, though treatment is not always simple or effective. TB is not something that is typically vaccinated against in the United States and it can be fatal if left untreated.

TB has been around for tens of thousands of years. It was often called "consumption" because of the dramatic weight loss it can cause. Before the 1940s, when the antibiotic streptomycin became available, there wasn't much that could be done for the illness. Fresh air, good nutrition, and sunlight were thought to be helpful but didn't always work. In some cases, doctors attempted to remove a diseased lung. From the 17th through the 19th centuries, it is believed that one in five people died from tuberculosis.

Still a leading killer worldwide, tuberculosis is less prevalent in the United States than it used to be. According to the Centers for Disease Control and Prevention (CDC), 9,029 new cases of TB were reported in the United States in 2018.

When a healthy person gets infected with TB, their immune system cells will usually wall off the infection and cause the TB bacteria to go into an inactive form that causes no symptoms and is not contagious; this is known as latent TB infection. It is possible to live with latent TB without ever developing the active form of the disease.

If the immune system is weakened, however, the infection can become active, causing symptoms and contagious disease. About 5% to 10% of infected people who do not receive treatment for latent TB infection will develop TB disease at some time in their lives. 

The signature symptom of active TB is a bad cough that produces blood-tinged phlegm and can last three or more weeks. Other symptoms include chest pain, fatigue, loss of appetite, weight loss, fever, chills, and night sweats.

Tuberculosis is an airborne disease, spread primarily via droplets released into the air after a contagious person coughs, spits, or sneezes. The risk for infection is greatest for those who spend long periods of time in closed environments—such as an airplane, bus, or small living space—with infected people. 

TB is a serious health problem in many countries, especially developing ones. It has been called a “disease of poverty” because it is more prevalent in places with challenging socioeconomic conditions that lead to a crowded living, malnutrition, and more. While tuberculosis is less prevalent in the United States, it remains a problem in hospitals, prisons, and homeless shelters, where crowded conditions prevail.

Those with weakened immune systems are especially at risk for TB. This includes children, the elderly, those with an immune-compromising disease or condition (like HIV), those taking immunosuppressive drugs (such as in the treatment of an autoimmune disease or after an organ transplant), and people undergoing cancer treatment.

If you suspect that you have active TB, call your healthcare provider to arrange for a TB test. The most commonly used one is the Mantoux skin test, which is performed by injecting a purified protein derivative of mycobacterium tuberculosis under the skin on your forearm. If you have an immune reaction, ​swelling will result at the injection site within two to three days.

Sometimes the skin test may be given too soon after exposure to the bacteria (before eight to 10 weeks) for an immune response to develop. If you do test positive, you will undergo further testing, including a chest X-ray and a bacterial culture or microscopic examination of coughed-up sputum (phlegm).

There are also blood tests used to diagnose TB, known as interferon-gamma release assays (IGRAs), though they are not used as frequently.

Tuberculosis is treated with antibiotics. Treatment usually consists of six to eight weeks of a combination of four drugs, followed by two of the medications for 18 weeks, for a total duration of six to nine months. The exact course prescribed to you depends on your case and overall health.

It is very important to follow your doctor’s instructions for TB treatment, even after symptoms subside. The full course of antibiotics is necessary to kill all of the TB bacteria. Failure to complete the full course can lead to ineffective treatment, longer duration of the illness, and antibiotic-resistant TB, the treatment options for which are less effective and have more side effects than first-line drugs.

If you receive a positive diagnosis of active tuberculosis, you will be instructed not to attend work or school until your doctor determines you are no longer contagious (usually about two to three weeks after starting treatment, but this may take up to six weeks). Until then, keep your distance from people with whom you have regular contact. Remember to cough into a tissue and discard it in a sealed bag. 

After release from the hospital, public health officials will provide you with guidelines for returning to work or school. People with whom you have had contact should be tested for infection.

While being diagnosed with active tuberculosis can be frightening, the prognosis is good. Most cases of TB are treatable and curable as long as you follow your doctor’s instructions and take your medicines exactly as prescribed.