What is tuberculosis?

Tuberculosis (TB) is an infectious disease caused by a bacterium called Mycobacterium tuberculosis. It’s a disease that usually affects lungs, but it can affect almost any part of your body.

TB is passed on from person to person by droplets carried in the air, usually from coughs and sneezes. Your body’s immune system, which fights infection, usually destroys the germs once they are inhaled and clears the body of infection.  In a small number of people, infection persists but the immune system successfully builds a defensive barrier around the bacteria. The bacteria stay in the body, but you won’t usually have any symptoms and can’t pass the infection on to other people. This is called latent TB.

Sometimes, the immune system fails to destroy the bacteria, or latent TB reactivates to cause an active infection years later. This is more likely to happen if your immune system becomes weakened by other problems such as HIV, poorly controlled diabetes, or if you are underweight. At first, a TB infection normally affects the lungs. This is called pulmonary TB. However, TB often spreads to the lymph nodes (glands throughout your body that are part of your immune system). It can also affect your bones, joints and kidneys. TB can also cause meningitis (inflammation of the membranes surrounding the brain and spinal cord), though this is rare.

What causes tuberculosis?

You can catch TB by breathing in droplets in the air that contain the bacterium M. tuberculosis. These are spread through the air when someone with TB coughs or sneezes. Only some people with TB in their lungs are infectious to others.

Although it is spread through the air, you need to be closely exposed to a person with TB for some time before you catch it. People most commonly catch TB from people they live or work with. When you start treatment for TB, you remain infectious to others for the first two weeks.

Although anyone can get TB, it’s quite difficult to catch in the UK. You’re more likely to get TB if you:

  • Already have a weakened immune system (for example, if you have HIV/AIDS or are taking medicines that suppress your immune system).
  • Have diabetes.
  • Have regular close contact with people who have TB lung infection.
  • Are young or elderly.
  • Live in overcrowded housing.
  • Are dependent on drugs or alcohol.
  • Are in poor health generally and have been for some time.

What are the symptoms of tuberculosis?

Depending on how effectively your immune system fights the infection, you may have:

  • No symptoms at all.
  • Minor symptoms, which then go as you fight the infection off.
  • Symptoms that develop in the months following infection.
  • Symptoms that develop years after you were infected.


The symptoms of tuberculosis infection in your lungs may include:

  • A persistent cough – there may also be lots of phlegm, sometimes containing blood.
  • Fever.
  • Tiredness.
  • Loss of appetite.
  • Weight loss.
  • Sweating, particularly at night.
  • Chest pain when you breathe in, caused by inflammation of the membranes lining your lungs (pleurisy).

If you have TB in other parts of your body, you may also have other symptoms such as swollen glands in your neck, pain in your joints or a headache.

How is tuberculosis diagnosed?

If you come to a TB clinic, we sometimes find that you do not have TB and there is another cause for your symptoms. If we think you have been exposed to TB, we will investigate to decide whether you have an active infection (evidence of infection on x-ray/ scans, suggestive symptoms and/or the presence of TB bacteria from samples) or latent TB which means the tests reveal evidence of exposure to TB bacteria but no active disease.

Active tuberculosis

To diagnose active TB infection, you will usually be asked to give at least three separate samples of your phlegm for testing. These will be examined in a laboratory to see if we can grow the tuberculosis bacterium from the samples. We will also routinely do blood tests, including tests of liver and kidney function, and a chest X-ray to look for active TB in the lungs and enlargement of lymph glands of the chest.

In some cases, if we are unable to grow the tuberculosis bacterium from your sputum samples but think that you have active tuberculosis in your lung, we may ask you to come in for the day for a bronchoscopy. This allows us to take a sample from deep in your lungs by passing a small flexible telescope (a bronchoscope) down the breathing tubes in order look for signs of infection and inflammation.  If you have enlarged lymph nodes in your chest, we may perform an EBUS (endobronchial ultrasound) to take a sample of the lymph-nodes in the chest safely using a very special bronchoscope which avoids the need for an operation. Both bronchoscopy and EBUS are quick, safe and painless day case procedures.

If you have other swollen lymph glands, for example in your neck, that we think may be affected with tuberculosis, we may suggest a biopsy of one of these first as this is the easiest way to diagnose glandular TB.

If you are diagnosed with active TB, those people who have been in close contact with you, such as family members or work colleagues, may also be tested for the infection.

Latent tuberculosis

To diagnose latent TB, you can have a skin test called a Mantoux. This test involves an injection just under your skin usually on the inside of your forearm. Over the next two to three days, a reaction to the injection will develop which is then graded. The greater the reaction, the more likely it is that you have TB exposure and, in this case, your doctor may ask you to have further tests to exclude active infection. This test may be positive if you have had a BCG immunisation against TB in the past. Latent TB can also be diagnosed with an Interferon Gamma Release Assay (IGRA) blood test which is not positive after previous BCG immunisation but is positive when there is latent TB infection.

Can tuberculosis be treated or prevented?

There is good news for people with tuberculosis! It can almost always be cured with medicine. But the medicine must be taken as the doctor or nurse tells you. The main cause of treatment failure is because of patients not taking the medicine exactly as directed, which is termed ‘non-adherence’.

Today, treatment involves four different kinds of antibiotics given in combination for the first two months. Thereafter, two are stopped, assuming good clinical progress, and the remaining antibiotics continued until the end of treatment (usually 6 months).  Multiple medicines are necessary to prevent the emergence of resistance, which would lead to treatment failure and the nightmare of multiple drug-resistant organisms.

Those patients who are coughing up mycobacteria in their sputum (smear positive) are infectious and, if possible, should avoid contact with other people for at least two weeks.

Patients do not require hospital admission in order to start treatment. For patients, the mycobacterium may not be visible in their sputum (smear negative), but the mycobacterium can be grown from their sputum after several days or weeks. These patients are not as infectious, but should still have therapy along conventional lines.

If you are diagnosed with latent TB, you will be offered treatment to eradicate any mycobacteria to prevent active TB in the future. This is called chemoprophylaxis and consists of either one antibiotic taken for 6 months or two antibiotics for 3 months.

The mycobacterium that causes TB can become resistant to the normal TB drugs, and some strains are resistant to several different drugs. These strains can cause very serious disease called multi-drug resistant tuberculosis (MDR-TB), and can be transmitted to others. MDR-TB can usually be treated successfully after identifying which drugs the organisms are still susceptible to. More worryingly, cases are now being seen of extensively drug resistant TB (XDR-TB) which are very hard to treat effectively, but these are still extremely rare in the United Kingdom.

Living with tuberculosis

You will need regular check-ups in the TB clinic to make sure your treatment is working. You will be seen regularly; every week or two initially (for active TB) to ensure there aren’t any problems with the medications. Subsequently, visits will be every month or two.

You must finish your medicine and take the drugs exactly as prescribed. If you stop taking the drugs too soon, you can become sick again. If you do not take the drugs correctly, the TB germs that are still alive can become resistant to the drugs.

Sometimes, the drugs used to treat TB can cause side effects. If you are taking medicine for preventive therapy or for active TB disease, let your doctor know if you begin having any unusual symptoms. In particular, you should inform the clinic if you have visual problems, nausea, vomiting, itchy skin or abdominal pain.

One of the antibiotics (rifampicin) causes bodily secretions to turn orange, including urine and tears, so wearing contact lenses can be a problem. We also give you a vitamin tablet along with the treatment as it helps prevent one of the medications (isoniazid) from affecting the nerves in the hands and feet.

Ongoing research into tuberculosis

It is important to grow colonies of TB bacteria in the laboratory using special culture techniques from the specimens we ask patients to provide, this confirms the diagnosis and also tells us which antibiotics the bacteria are sensitive to. Growing TB bacteria can take up to 6 weeks and samples from glandular TB are more difficult to culture – over half of these samples never grow and therefore treatment proceeds on the basis of clinical probability. As a result we need better methods of confirming a diagnosis of TB, and this is an active area of research at University College London.

Visit our research pages for more information on our research.

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