Tuberculosis (TB) explained: symptoms, testing and cure

What TB is and how it spreads

Tuberculosis is caused by a bacterium called Mycobacterium tuberculosis. It usually affects the lungs (pulmonary TB) but can also affect the lymph nodes, bones, kidneys, brain and other organs. TB spreads through the air when a person with active TB in their lungs coughs, sneezes or speaks, releasing tiny droplets that others can breathe in. It generally needs prolonged, close contact to spread, such as living in the same household, rather than brief everyday encounters. Not everyone who breathes in the bacteria becomes ill; the immune system often contains the infection. TB is more common in some parts of the world and among people whose immune systems are weakened.

Latent versus active TB

A key idea in understanding TB is the difference between latent and active infection. In latent TB, the bacteria are present in the body but kept in check by the immune system. The person has no symptoms, feels well, and cannot pass TB to others — but the bacteria could reactivate later, especially if immunity weakens. In active TB, the bacteria are multiplying and causing illness, with symptoms, and pulmonary active TB can be infectious to others. Treating latent TB with medicine can prevent it from ever becoming active, which is why people at higher risk are sometimes screened and offered preventive treatment even when they feel completely well.

Recognising the symptoms

The symptoms of active TB often develop slowly over weeks. In lung TB, the classic features are a persistent cough lasting more than three weeks, sometimes bringing up phlegm or blood, along with a high temperature or night sweats, unintended weight loss, tiredness and loss of appetite. When TB affects other parts of the body, symptoms depend on the site — for example, swollen lymph nodes in the neck, back pain, or, rarely, headaches and confusion if it reaches the brain. Because these symptoms overlap with many other conditions, a persistent cough or unexplained weight loss and night sweats should always be checked by a doctor.

Testing and diagnosis on the NHS

Diagnosing TB usually combines several tests. For suspected lung TB, a chest X-ray can show changes, and samples of phlegm are examined and cultured in the laboratory to find and grow the bacteria, which also reveals which antibiotics will work. Latent TB is detected with a blood test or a skin test that shows whether the immune system has met the bacteria. Where TB affects other organs, scans and tissue samples may be needed. TB is a notifiable disease in the UK, meaning cases are reported to public health teams who trace and screen close contacts to find and treat further infections and stop the spread.

Treatment, cure and prevention

The good news is that TB is usually curable. Treatment involves a combination of antibiotics taken for several months — a longer course than most infections — to clear the bacteria completely. It is essential to take every dose and finish the full course, even once you feel better, because stopping early can leave surviving bacteria that become resistant to the medicines and much harder to treat. Specialist TB nurses support people through treatment, sometimes supervising doses. The BCG vaccine offers protection, particularly against severe TB in young children, and in the UK is offered to babies and others at higher risk rather than to the whole population.