Tuberculosis is a bacterial infection that usually attacks the lungs, spreads through the air, and can be treated with antibiotics

Tuberculosis (TB) is caused by bacteria called Mycobacterium tuberculosis. When a person with active TB in their lungs coughs, sneezes, or speaks, they release tiny droplets containing the bacteria into the air. Another person breathes in those droplets and the bacteria settle in their lungs. This is how TB spreads—through the air, not through touch, food, or shared utensils.

Not everyone who breathes in TB bacteria gets sick. Your immune system may fight off the infection and stop it from growing. This is called latent TB infection—you carry the bacteria but have no symptoms and cannot spread it to others. Some people's immune systems cannot control the infection, and the bacteria multiply. This is called active TB disease, and it causes symptoms and can spread to others.

TB is treatable. A course of antibiotics lasting several months can cure active TB disease. Without treatment, TB can damage the lungs and spread to other parts of the body, including the brain, kidneys, and bones. It can be fatal.

Key Takeaways

  • TB spreads through the air when a person with active lung TB coughs or sneezes, not through touch or shared food.
  • Latent TB infection means you carry the bacteria but have no symptoms and cannot spread it; active TB disease means the bacteria are multiplying and causing illness.
  • A skin test or blood test can detect TB infection; a chest X-ray and sputum test confirm active TB disease.
  • Active TB disease is curable with a course of antibiotics that usually lasts four to six months.
  • People at higher risk include those with weakened immune systems, close contacts of someone with active TB, and people living in crowded conditions.

Active TB disease versus latent TB infection

The difference between these two states matters for treatment and for whether you can spread TB to others. With latent TB infection, the bacteria are in your body but dormant—your immune system is holding them in check. You have no symptoms, you feel well, and you cannot spread TB to anyone else. You may never develop active disease. But the bacteria can reactivate later, especially if your immune system weakens due to age, illness, or certain medications.

With active TB disease, the bacteria are multiplying and damaging tissue, usually in the lungs. You have symptoms: a cough lasting more than three weeks, chest pain, coughing up blood or mucus, fever, chills, and night sweats. You can spread TB to others through the air. Active TB disease requires treatment with antibiotics.

A person with latent TB infection may be offered preventive antibiotics to reduce the risk that the infection will become active later. This is especially common if you are young, have a weakened immune system, or were recently exposed to someone with active TB.

How TB spreads and who is at higher risk

TB spreads only from a person with active TB disease in the lungs or throat. The bacteria travel in droplets released when that person coughs, sneezes, speaks, or sings. You cannot catch TB from shaking hands, sharing food or drinks, sharing a bed, or touching someone's clothes. You cannot catch it from someone with latent TB infection.

The risk of catching TB increases with close, prolonged contact. Healthcare workers, family members, and others who spend hours near a person with active TB are at higher risk than someone who passes them briefly on the street. Crowded indoor spaces with poor ventilation—prisons, shelters, nursing homes—increase transmission risk.

Certain groups have higher risk of developing active TB disease if infected. These include people with HIV, people taking immunosuppressive medications, people with diabetes, people who smoke, people with kidney disease, and people who are very young or very old. Malnutrition and alcohol use disorder also increase risk.

Symptoms of active TB disease

Active TB disease usually develops slowly. Symptoms may appear weeks or months after infection. The most common sign is a cough that lasts more than three weeks. Other symptoms include chest pain when breathing or coughing, coughing up blood or blood-tinged mucus, fever (usually in the afternoon or evening), chills, night sweats that may soak your clothes, and weight loss or loss of appetite.

These symptoms can be caused by other conditions, so a cough lasting more than three weeks should be evaluated by a doctor. TB can also affect parts of the body other than the lungs—the kidneys, spine, brain, or lymph nodes—and cause different symptoms depending on the location.

How TB is detected and diagnosed

Two main tests detect TB infection: the tuberculin skin test (also called the Mantoux test) and TB blood tests. Both show whether you have been infected with TB bacteria, but neither tells you whether the infection is latent or active.

For the skin test, a nurse injects a small amount of fluid under the skin on your forearm. You return 48 to 72 hours later, and the nurse measures any swelling. A certain amount of swelling means the test is positive—you have TB infection. Blood tests work similarly: they measure your immune response to TB antigens. Blood tests are faster and do not require a return visit.

If a skin test or blood test is positive, a chest X-ray is done to look for signs of active TB disease in the lungs. If the X-ray shows suspicious areas, a sputum sample (mucus coughed up from the lungs) is tested for TB bacteria. A positive sputum test confirms active TB disease. Some labs also perform drug-resistance testing to determine which antibiotics will work.

Treatment of active TB disease

Active TB disease is treated with a combination of antibiotics taken by mouth. The standard treatment is four drugs—isoniazid, rifampicin, pyrazinamide, and ethambutol—taken together for two months, followed by isoniazid and rifampicin alone for four more months. The full course is six months.

It is critical to take all doses as prescribed, even after you start feeling better. Stopping early or skipping doses allows the bacteria to survive and develop resistance to the drugs. Drug-resistant TB is much harder to treat and requires longer courses of different, stronger antibiotics with more side effects.

Most people stop being contagious after about two weeks of treatment, but they must continue taking all the medication. Your doctor will monitor your progress with follow-up visits and sometimes repeat chest X-rays or sputum tests to confirm the infection is clearing.

Prevention and exposure response

If you have been in close contact with someone who has active TB disease, you should be tested. Close contact usually means living in the same household, working in the same office, or spending several hours together in a poorly ventilated space. Testing should happen as soon as possible after exposure.

If your test shows latent TB infection after exposure, your doctor may recommend preventive antibiotics. These are usually taken for three to nine months, depending on the drug used and your risk factors. Preventive treatment reduces the chance that latent infection will become active disease.

In healthcare settings and congregate facilities like shelters and prisons, TB control measures include isolating people with active TB disease, ensuring good ventilation, and testing staff and residents regularly.

TB in different parts of the body

While TB most commonly affects the lungs, it can spread to other organs. Extrapulmonary TB can affect the lymph nodes, bones and joints, kidneys, brain (causing meningitis), and other sites. Symptoms depend on which organ is affected. TB meningitis, for example, causes severe headache, stiff neck, and confusion. TB of the spine causes back pain and can lead to paralysis if untreated.

Extrapulmonary TB is less common than pulmonary TB but is more common in people with weakened immune systems, including those with HIV. Diagnosis may require imaging, biopsies, or fluid samples from the affected area. Treatment is the same as for pulmonary TB—a combination of antibiotics—though the duration may be longer for some forms.

Frequently Asked Questions

Can you catch TB from someone with latent TB infection?

No. Latent TB infection means the bacteria are dormant and not multiplying. The person has no symptoms and cannot spread TB to others. Only people with active TB disease in the lungs or throat can spread the infection through the air.

How long does it take for TB to develop after exposure?

TB can develop anytime after infection, but it usually appears within the first two years. Some people develop active disease within weeks; others may not develop symptoms for years or decades. This is why people exposed to TB are tested and sometimes given preventive treatment.

Is TB curable?

Yes. Active TB disease is curable with a full course of antibiotics lasting four to six months. It is important to take all doses as prescribed. Without treatment, TB can cause serious damage and death.

What happens if TB antibiotics do not work?

If TB bacteria are resistant to standard antibiotics, drug-resistance testing identifies which drugs will work. Treatment then uses different, stronger antibiotics for a longer period—often 18 to 20 months or more. Drug-resistant TB is harder to treat but still curable in most cases.

Can you get TB more than once?

Yes, though it is uncommon. After treatment for active TB, you develop some immunity, but it is not complete. Reinfection can occur if you are exposed to TB bacteria again, especially if your immune system is weakened.