Tuberculosis (too-ber-ku-LO-sis) is a bacterial infection that spreads through the air and usually affects the lungs. Worldwide, it kills more people than any other infectious disease.

An Ancient Disease

Hippocrates (c. 460–c. 377 BCE), a Greek physician who in modern times is called “the father of medicine,” accurately described tuberculosis (TB) about 2,400 years ago when he coined the term “phthisis,” which means to melt and to waste away. In later years, TB was called consumption because people with TB tended to waste away as if they were being slowly consumed.

What Is Tuberculosis?

X-ray of lung (right) infected with Mycobacterium tuberculosis, the bacterium that causes tuberculosis. This disease has infected humans for thousands of years.

X-ray of lung (right) infected with Mycobacterium tuberculosis, the bacterium that causes tuberculosis. This disease has infected humans for thousands of years.

Considered one of the world's deadliest diseases, one-third of the world's population is infected with TB. In 2013, 9 million people around the world became sick with TB. Of this number, 1.5 million people died. It is considered the leading killer of people infected with HIV * . The number of TB cases has been slowly decreasing in the United States. Data from the 2010s show an average decline of 3 to 4 percent of new cases every year.

Not everyone who is infected with TB bacteria (called primary infection) gets sick or infects other people. Not everyone infected with TB develops active TB (called secondary infection.) Of the people who are infected and develop active disease, about one-third to one-half manifest illness in the first two months to two years after they are initially infected; the remainder develop active TB later in life. People with primary TB infection are protected from developing active TB by their body's immune system * , but they still carry the bacteria in their bodies. As long as the infection is inactive, they cannot spread TB. But they can develop active (secondary) TB years later if their immune systems are weakened by other diseases such as HIV/AIDS * or diabetes * or by alcohol or drug abuse. Most people with active TB who are treated can be cured. If left untreated, TB is fatal 40 to 60 percent of the time. Individuals diagnosed with TB infection can be prescribed preventive therapy, which can reduce the lifetime risk of developing active disease by at least 70 percent.

How Is Tuberculosis Spread?

When people with active TB of the lungs cough or sneeze, they spread the bacteria that cause TB through the air. Other people who breathe the same air may become infected with the bacteria, which can lodge in the lungs and begin to multiply and spread. From there, the bacteria can move through the blood and settle in almost any other part of the body, including the urinary tract, brain, kidneys, lymph nodes * , bones, joints, peritoneum * , and heart.

Spending time in close quarters with a person who has untreated active TB is the most common way of becoming infected. But even with close contact, only one-third of people who are exposed to TB infection become infected. Within a few weeks of the start of effective treatment, patients are no longer contagious. TB in parts of the body other than the lungs is usually not contagious. People who have primary TB cannot spread it to others.

Who Gets Tuberculosis?

TB can affect anyone, but some people are more likely to get it than others:

HIV and TB: A Lethal Combination

Because HIV/AIDS infection weakens the immune system, patients who have HIV/AIDS are at high risk for contracting TB. Approximately 13 million people around the globe are infected with both HIV and TB. TB is more likely to spread to other areas of the body in people with HIV, and multidrug-resistant (MDR) TB is much more dangerous in these patients. TB infection in patients who have HIV/AIDS can be cured if found and treated early.

The red spot on the arm indicates a positive skin test for TB.

The red spot on the arm indicates a positive skin test for TB.
Dr. P. Marazzi/Science Source.

What Are the Symptoms of Tuberculosis?

Primary TB does not cause any symptoms. The symptoms of secondary (active) TB depend on where in the body the TB bacteria are growing.

TB of the lungs may cause a cough that does not go away and pain in the chest. The affected individual may also cough up blood or sputum * . Other common symptoms include feeling tired all of the time, weight loss, lack of appetite, fever, chills, and sweating at night. People with secondary TB may feel sick soon after infection or may develop symptoms gradually over weeks or months; they may be highly contagious until treated. Some people with active TB feel well and only cough occasionally.

TB bacteria typically infect the lungs, but they can infect almost any part of the body:

How Is Tuberculosis Diagnosed?


Archeologists have found evidence of TB in skeletons from Peru that are 1,300 years old and in Egyptian skeletons dating back 3,400 years. But TB apparently did not emerge as a major killer until the 1600s in Europe.

By the 1800s, the Industrial Revolution had created ideal conditions for TB to spread—overworked, underfed people crowded together in tenements and factories with poor ventilation. TB became the leading killer in many European and U.S. cities.

It was unclear whether TB was inherited or infectious until the 1880s, when the German physician Robert Koch (1843–1910) identified the TB bacterium. Treatment consisted of rest, rich food, and fresh air, often provided in special TB hospitals called sanatoriums that were built in mountain areas.

Streptomycin, an antibiotic that kills TB bacteria, was introduced in the 1940s. Isoniazid, another effective antibiotic, came into use in the 1950s. These drugs dramatically lowered the number of TB cases over the next few decades. Both remain in use today along with other drugs. As drug-resistant strains of TB continue to emerge, research to find better treatments is ongoing.

How Is Tuberculosis Treated?

Primary tuberculosis

People with primary TB who are in high-risk groups for developing active TB may be given medication to help ward off the illness. This treatment is called preventive therapy. People under age 35 with primary TB who are not in high-risk groups may also benefit from preventive therapy. The goal is to kill the bacteria that are not doing any harm now but that could cause active TB in the future. The medication usually given for this purpose is called isoniazid (INH). To kill these bacteria, INH must be taken every day for 6 to 12 months.

Secondary (active) tuberculosis

Secondary (active) TB can often be cured with medication. People with secondary TB usually take several different drugs because doing so is more effective in killing all the bacteria and preventing the formation of resistant bacteria that cannot be killed by drugs.

Germs That Resist Arrest

Multidrug-resistant (MDR) tuberculosis, caused by bacteria that cannot be killed by regular tuberculosis drugs, is very dangerous. Even with treatment, 40 to 60 percent of people with MDR tuberculosis die. People with MDR tuberculosis must take special medications that do not work as well as the usual tuberculosis drugs and that have more side effects.

MDR tuberculosis occurs when tuberculosis patients stop taking their prescribed medications or do not take them as directed. Patients often stop taking the drugs when they begin to feel better. But because tuberculosis bacteria can survive inside the body for several months during treatment, they are ready to spring back into activity when the medication disappears.

One way to fight this problem is through directly observed therapy (DOT). In DOT, patients must take their medications regularly in the presence of a health professional. Home visits by health professionals to supervise the taking of medications or free transportation and meals are often provided to encourage patients to take part in this type of program.

MDR tuberculosis is common in some parts of the world, including Southeast Asia, Latin America, Haiti, and the Philippines.

Although they usually feel better after a few weeks of treatment, people with active TB must continue to take their medication correctly for the full length of the treatment or they can become sick again. Because people with TB of the lungs can spread the infection to others, they need to stay home from school or work until they are no longer infectious to others, which usually takes several weeks.

People with TB who are sick enough to go to the hospital may be put in a special room with an air ventilation system that keeps the bacteria from spreading. Doctors, nurses, and others who work in such rooms must wear special facemasks to protect themselves from breathing in the bacteria.

How Can the Spread of Infection Be Stopped?

The Centers for Disease Control and Prevention (CDC) recommends that certain people at risk for becoming infected with TB get the skin test yearly so that treatment can begin immediately if they are found to have TB. These include:

People who have TB can keep from spreading the infection by taking all their medication exactly as prescribed; visiting their doctors regularly; staying away from people until they are no longer infectious to others; covering their mouths with a tissue when they cough, sneeze, or laugh; and airing out rooms often.

TB bacteria can only be spread through the air. Other people cannot be infected by shaking hands, sitting on toilet seats, or sharing dishes or personal items with people who have TB. If close contact with someone who has TB is necessary, a special type of facemask (called a respirator) should be worn.

Bacillus Calmette-Guérin (BCG) is a vaccine * that can help protect people against tuberculosis infection. It does not always work and may cause a positive reaction to the tuberculosis skin test, making it harder to tell if people become infected despite the vaccine. BCG is not widely used in the United States, but it is often given to babies and young children in countries where tuberculosis is common.

See also AIDS and HIV Infection • Antibiotic Resistance • Bacterial Infections • Pneumonia


Books and Articles

Bynum, Helen. Spitting Blood: The History of Tuberculosis. Oxford, UK: Oxford University Press, 2015.

Kaufmann, Stefan H. E., Eric Rubin, and Ali Zumla. Tuberculosis. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press, 2014.


Centers for Disease Control and Prevention. “Tuberculosis.” (accessed March 4, 2016).

MedlinePlus. “Tuberculosis.” U.S. National Library of Medicine. (accessed March 4, 2016).

National Institute of Allergy and Infectious Diseases. “Tuberculosis (TB).” (accessed March 4, 2016).


American Lung Association. 55 W. Wacker Dr., Ste. 1150, Chicago, IL 60601. Toll-free: 800-LUNGUSA. Website: (accessed March 4, 2016).

Centers for Disease Control and Prevention, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention. 1600 Clifton Rd., Atlanta, GA 30333. Toll-free: 800-232-4636. Website: (accessed March 4, 2016).

National Institute of Allergy and Infectious Diseases. 5601 Fishers Lane, MSC 9806, Bethesda, MD 20892-9806. Toll-free: 866-284-4107. Website: (accessed March 4, 2016).

World Health Organization. Avenue Appia 20, CH 1211 Geneva 27, Switzerland. Telephone: 41 22 791 2111. Website: (accessed March 4, 2016).

* HIV, or human immunodeficiency virus (HYOO-mun ih-myoono-dih-FIH-shen-see), is the virus that causes AIDS (acquired immunodeficiency syndrome), an infection that severely weakens the immune system.

* immune system (im-YOON SIStem) is the system of the body composed of specialized cells and the substances they produce that helps protect the body against disease-causing germs.

* AIDS, or acquired immunodeficiency (ih-myoo-no-dih-FIH-shensee) syndrome, is an infection that severely weakens the immune system; it is caused by the human immunodeficiency virus (HIV).

* diabetes (dye-uh-BEE-teez) is a condition in which the body's pancreas does not produce enough insulin or the body cannot use the insulin it makes effectively, resulting in increased levels of sugar in the blood. This can lead to increased urination, dehydration, weight loss, weakness, and a number of other symptoms and complications related to chemical imbalances within the body.

* lymph nodes (LIMF) are small, bean-shaped masses of tissue containing immune system cells that fight harmful microorganisms. Lymph nodes may swell during infections.

* peritoneum is the membrane that lines the abdominal cavity.

* sputum (SPYOO-tum) is a substance that contains mucus and other matter coughed out from the lungs, bronchi, and trachea.

* vaccine (vak-SEEN) is a preparation of killed or weakened germs, or a part of a germ or product it produces, given to prevent or lessen the severity of the disease that can result if a person is exposed to the germ itself. Use of vaccines for this purpose is called immunization.

  This information is not a tool for self-diagnosis or a substitute for professional care.