Tuberculosis is a bacterial infection that usually attacks the lungs

Tuberculosis (TB) is an infection caused by bacteria called Mycobacterium tuberculosis. The infection spreads through the air when a person with active TB coughs, sneezes, or speaks. Most people who breathe in the bacteria do not get sick — their immune system stops the infection before symptoms start. But some people develop active TB disease, which damages the lungs and can spread to other parts of the body if left untreated.

TB is treatable with antibiotics, but the treatment takes several months and requires taking multiple drugs on schedule. Without treatment, TB can be fatal. The disease is less common in the United States than it once was, but it still occurs and remains a serious global health problem.

Key Takeaways

  • Tuberculosis spreads through the air from a person with active TB disease and can be prevented by early detection and treatment.
  • Most people infected with TB bacteria never develop symptoms because their immune system contains the infection, a state called latent TB.
  • Active TB disease causes symptoms like persistent cough, chest pain, and coughing up blood, and requires immediate medical attention.
  • Doctors diagnose TB using a skin test, blood test, or chest X-ray, depending on whether TB is suspected or confirmed.
  • TB treatment involves taking a combination of antibiotics for at least six months, and completing the full course is essential to cure the disease and prevent drug-resistant TB.

Latent TB infection versus active TB disease

When TB bacteria enter your body, one of two things happens. In most cases, your immune system walls off the bacteria so they cannot multiply or cause illness. You have no symptoms, feel fine, and cannot spread TB to others. This is called latent TB infection. A person with latent TB can live their entire life without ever developing active disease.

In other cases, the immune system cannot contain the bacteria. The bacteria multiply in the lungs and cause illness. This is active TB disease. A person with active TB feels sick, has symptoms, and can spread the infection to others. Active TB can develop weeks after infection or years later, especially if something weakens the immune system.

People at higher risk of developing active TB include those with HIV, those taking medications that suppress the immune system, people with diabetes, and those who are very young or very old. Malnutrition, alcohol use disorder, and smoking also increase risk.

Symptoms of active tuberculosis

Active TB usually starts slowly. The first sign is often a cough that lasts more than three weeks. As the disease progresses, you may cough up sputum (mucus) that contains blood. Other symptoms include chest pain when breathing or coughing, fever that is often worse in the afternoon, night sweats that soak your clothes, and weight loss or loss of appetite.

These symptoms can resemble other lung conditions, which is why a doctor's evaluation is important. If you have a cough lasting longer than three weeks, especially if you also have fever or night sweats, see a doctor. TB is treatable, and early diagnosis makes treatment more effective and reduces the chance of spreading the disease to others.

How doctors test for tuberculosis

Doctors use three main tests to detect TB. The tuberculin skin test (also called the Mantoux test) involves injecting a small amount of TB protein under the skin on your forearm. A nurse checks the injection site 48 to 72 hours later. A raised bump of a certain size means TB infection is likely, though the test cannot tell whether you have latent or active TB.

The interferon-gamma release blood test measures how your immune system responds to TB proteins in a blood sample. This test is more specific than the skin test and is not affected by prior TB vaccination. Results come back within a few days.

If either test suggests TB, a doctor will order a chest X-ray to look for signs of active TB in the lungs. If the X-ray shows changes typical of TB, the doctor will collect a sputum sample (mucus you cough up) and send it to a lab to look for TB bacteria under a microscope or grow the bacteria in culture. This confirms active TB disease and allows the lab to test which antibiotics will work against the specific bacteria.

How tuberculosis spreads

TB spreads through the air. When a person with active TB in the lungs coughs, sneezes, speaks, or sings, they release tiny droplets containing TB bacteria. Another person breathes in these droplets and the bacteria settle in their lungs. Close, prolonged contact increases the risk of transmission — brief encounters with a stranger are unlikely to spread TB, but living with or working closely with someone who has active TB raises the risk significantly.

TB does not spread through shaking hands, sharing food or drinks, touching or hugging, sharing clothing or bedding, or sharing a toilet. You cannot get TB from touching a person's skin. Once a person with active TB starts antibiotic treatment, they usually stop being contagious within two weeks, even though the infection is not yet cured.

What happens after diagnosis

If you are diagnosed with latent TB, your doctor will discuss whether treatment is right for you. People with latent TB who are at high risk of developing active disease — such as those with HIV, young children, or those who recently had contact with someone with active TB — are usually offered preventive treatment. This involves taking one or more antibiotics for several months to reduce the risk of active TB developing.

If you are diagnosed with active TB, treatment begins immediately. Standard TB treatment uses a combination of four antibiotics taken together for the first two months, followed by two antibiotics for four more months. The exact drugs and duration depend on the type of TB and whether the bacteria show resistance to certain antibiotics. You will have follow-up appointments to check how you are responding and to make sure you are taking the medications correctly.

Completing the full course of treatment is critical. Stopping early allows the bacteria to survive and can lead to drug-resistant TB, which is much harder to treat. Your doctor or a nurse may watch you take each dose to help ensure you finish the entire course.

Drug-resistant tuberculosis

Some TB bacteria develop resistance to the standard antibiotics used to treat TB. Multidrug-resistant TB (MDR-TB) resists at least two of the main TB drugs. Extensively drug-resistant TB (XDR-TB) resists even more drugs. Drug-resistant TB develops when treatment is incomplete or when the wrong drugs are used.

Drug-resistant TB is harder to cure and requires longer treatment with more medications, some of which have serious side effects. It spreads the same way as regular TB and is just as contagious. The best way to prevent drug-resistant TB is to complete TB treatment exactly as prescribed, even when you start feeling better.

Frequently Asked Questions

Can you get tuberculosis from someone who has latent TB?

No. People with latent TB have no symptoms and cannot spread the infection to others. Only people with active TB disease in the lungs can transmit TB through the air. This is why testing and early detection are important — they identify infection before it becomes contagious.

How long does TB treatment take?

Standard TB treatment takes at least six months. The first two months use four drugs, and the next four months use two drugs. Some cases require longer treatment, especially if the bacteria are drug-resistant. Your doctor will tell you the expected duration based on your specific situation.

What should I do if I think I have been exposed to tuberculosis?

Contact your doctor and mention the exposure. Your doctor will perform a TB test to see whether you have been infected. If the test is positive, further testing will determine whether you have latent or active TB. Early detection allows treatment to begin before active disease develops.

Can tuberculosis come back after treatment?

Relapse is uncommon if you complete the full course of treatment correctly. However, a person who has had TB can be infected again by someone else with active TB. This is a new infection, not a return of the old one. People who have been treated for TB should still follow the same precautions as anyone else to avoid exposure.

Is tuberculosis preventable?

TB cannot be prevented by avoiding exposure alone, since many people are infected without knowing it. However, people with latent TB can take preventive antibiotics to reduce the risk of developing active disease. For people with active TB, early treatment stops transmission and prevents others from becoming infected.