Tuberculosis (TB) explained: cause, symptoms, treatment and prevention

Cause and spread

TB is caused by a single bacterium, Mycobacterium tuberculosis. When a person with infectious TB of the lungs or voice box coughs, sneezes, talks loudly or sings, tiny droplets carrying the bacteria float in the air, and another person nearby can breathe them in. Prolonged close contact is usually needed for infection to take hold; TB is not spread by sharing food, shaking hands or touching surfaces.

India carries the largest share of the global burden: in 2024, about a quarter of all new TB cases worldwide were in India, followed by Indonesia, the Philippines, China and Pakistan. Overall, an estimated 10.7 million people fell ill with TB in 2024 and 1.23 million died, making TB the world's leading cause of death from a single infectious agent.

Infection versus disease

Most people who breathe in TB bacteria do not become ill. Their immune system walls the bacteria off, producing a latent TB infection: they feel well, have no symptoms and cannot spread the germ to others. Only about 5 to 10% of infected people eventually develop active TB disease, when the bacteria multiply and damage organs.

The risk of progressing to disease is highest in the first months after infection and stays high for about two years, though disease can appear many years later. Babies and young children face a higher risk if infected, as do people with weakened immunity from HIV, diabetes, undernutrition, tobacco use or harmful alcohol use.

Symptoms and diagnosis

TB most often affects the lungs, but it can also reach the kidneys, brain, spine and skin, and symptoms depend on the organ involved. The classic signs of lung TB are a prolonged cough, sometimes with blood, chest pain, weakness, fatigue, weight loss, fever and night sweats. Symptoms may stay mild for months, which is one reason people can spread TB without realising they are ill, and some people with active disease have no symptoms at all yet can still pass it on.

Diagnosis combines symptoms, a chest X-ray and laboratory tests. The World Health Organization recommends rapid diagnostic tests, including molecular assays, as the first test for anyone with TB symptoms, since they can give initial results within 48 hours and also detect drug resistance. Skin tests and blood tests (interferon gamma release assays) identify TB infection and help decide who should receive preventive treatment.

Treatment, drug resistance and prevention

TB disease is treated with a combination of antibiotics, most commonly rifampicin, isoniazid, pyrazinamide and ethambutol, taken daily, usually for 4 to 6 months, though some cases need longer. Stopping early is dangerous: it lets surviving bacteria become resistant and can turn a curable illness into a much harder one. Drug-resistant TB, which does not respond to rifampicin and isoniazid, the two most effective first-line drugs, needs different, longer and more costly treatment, although shorter all-oral regimens of about 6 months are now available for eligible patients.

Prevention rests on early care-seeking for a persistent cough, fever or unexplained weight loss, screening of close contacts and other high-risk groups, completing preventive treatment when prescribed, and cough hygiene such as wearing a mask and covering the mouth when coughing. In many countries, the BCG vaccine is given to babies to protect children from the most severe forms of TB. This article gives general educational information only, not personal medical advice.

Editorial disclosure

This article was researched and published with AI assistance. No human prepublication review is claimed. Report factual errors through our contact page.