Tuberculosis (TB) is an infection caused by Mycobacterium tuberculosis. It most often affects the lungs but can also affect other parts of the body, including the lymph nodes, kidneys, spine and brain. TB is preventable and curable, but active TB disease requires medical treatment.
Inactive TB and active TB disease
People with inactive TB infection have TB bacteria in the body but do not feel sick, have no symptoms and cannot spread TB to others. Without treatment, inactive infection can later develop into active TB disease.
Active TB disease occurs when the bacteria multiply and cause illness. TB affecting the lungs or throat can spread to other people through the air.
Symptoms
Symptoms of active pulmonary TB can develop gradually and may include:
- a cough lasting three weeks or longer
- coughing up sputum or blood
- chest pain
- fever or chills
- night sweats
- unexplained weight loss or reduced appetite
- fatigue or weakness
TB outside the lungs can cause other symptoms depending on the organ involved, such as swollen lymph nodes, back pain, blood in the urine, headache or confusion.
How TB spreads
TB bacteria spread through the air when a person with infectious TB disease of the lungs or throat coughs, speaks or sings. Transmission is more likely after prolonged or repeated close indoor contact. Inactive TB infection is not contagious.
Who should be tested?
Testing may be recommended for people with TB symptoms, close contact with someone who has active TB disease, or other factors that increase the risk of infection or progression to active disease. A healthcare professional can determine whether testing is appropriate.
Diagnosis
Tests for TB infection include a TB blood test, also called an interferon-gamma release assay (IGRA), and the tuberculin skin test. A positive infection test does not by itself show whether TB is inactive or active.
When active TB is suspected, evaluation may include medical history, examination, chest imaging and laboratory testing of sputum or other samples. Testing for drug resistance helps guide treatment when TB bacteria are identified.
Treatment
Both inactive TB infection and active TB disease can be treated. Treatment for active TB uses a combination of medicines and may last several months. The exact regimen depends on the site of disease, drug susceptibility, other health conditions and possible medicine interactions.
It is important to take TB medicines exactly as prescribed and complete treatment. Missing doses or stopping early can lead to treatment failure, recurrence and drug-resistant TB.
Preventing spread
People with infectious active TB may need temporary precautions to reduce transmission until their healthcare team determines that they are no longer infectious. Close contacts may be offered testing. The BCG vaccine is used in many countries, particularly to protect young children from severe forms of TB.
When to seek medical care
Arrange medical assessment for a persistent cough, coughing up blood, unexplained weight loss, prolonged fever or night sweats, particularly after possible TB exposure or if you have a condition that weakens the immune system.
Seek urgent medical care for severe breathing difficulty, significant coughing of blood, severe chest pain, collapse, new confusion or rapidly worsening illness. Use your local emergency medical service for severe or life-threatening symptoms.
Related topics
Sources and further reading
Last reviewed: 4 September 2026.