What you need to know about tuberculosis (TB)

TB or tuberculosis is an infectious disease that most commonly affects the lungs. In the UK, for every 100,000 people, almost 9,000 will develop TB.

It is caused by the bacterium Mycobacterium tuberculosis and is spread through droplets released into the air when an individual with TB coughs or sneezes. 

Here, we will explore tuberculosis symptoms, diagnosis, risk factors for infection and treatment.

Types of tuberculosis

The vast majority of TB cases are pulmonary TB, that is, tuberculosis that affects the lungs. 

Less commonly, TB can affect tissues and organs outside the lungs. This is called extrapulmonary TB and includes, for example, spinal TB, lymphatic TB and gastrointestinal TB. 

TB can also be categorised according to whether it is active or latent. If an individual has latent TB, they are infected with the bacteria but do not have any symptoms and cannot spread the infection. Active TB refers to an infection that results in symptoms.

How is tuberculosis spread?

Individuals with active pulmonary TB are contagious. They can spread TB through fluid droplets that escape into the air when they cough, sneeze, spit, laugh or sing. 

While TB is spread through the air, it is not as contagious as flu. Consequently, it is usually spread from one person to the next through close contact over a prolonged period of time. 

TB cannot be spread through sharing food, drinks, cooking utensils, clothes or linen, or through kissing or sexual intercourse. 

When an uninfected person breathes in droplets containing Mycobacterium tuberculosis, the bacteria pass through their airways and settle in tiny air sacs called alveoli at the ends of small branches of their airways (bronchioles). Here, the bacteria can multiply. 

In some cases, particularly if an individual has a weakened immune system, TB will spread from the lungs to other organs. 

Risk factors for tuberculosis infection

Anyone of any age can become infected with TB if they come into contact with someone who has active pulmonary TB. 

However, your risk is higher if you have a weakened immune system, for example, if you have HIV, AIDs or leukaemia, are undergoing chemotherapy or are taking steroids or immunosuppressants for a long period of time (eg after having an organ transplant).

You are also more likely to be infected with TB if you frequently travel to places where there is a high burden of TB, such as South East Asia, Africa and Eastern Europe, or if you regularly interact with individuals who spend extended periods of time in these places. 

Vaccination against TB 

If you will be spending more than three months in a country with a high burden of TB and are either under 16 and staying with locals or over 16 and will work as a health worker likely to encounter infected individuals, it is recommended that you are vaccinated against TB. 

The vaccine against TB is called the BCG (Bacillus Calmette-Guérin) vaccine. It is given as a single injection into the upper arm. 

The BCG vaccine is also provided on the NHS for newborns and children aged 1–16 who meet certain criteria. Specifically, the vaccine is given if they have a parent or grandparent who was born in a country with a high burden of TB or if they will be living with or in close regular contact with someone who has previously had TB or currently has TB. 

The BCG vaccine offers high levels of protection when given in childhood and slightly less protection when given in adulthood. 

Symptoms of tuberculosis

The most common symptom of pulmonary TB is a cough that lasts for over three weeks (persistent cough). This is usually a wet or productive cough, which means when you cough, you bring up phlegm or mucus from your airways. In some cases, the phlegm produced when you cough may contain blood. 

TB also causes a loss of appetite, unintentional weight loss, fever, night sweats and fatigue. In cases where it spreads beyond the lungs, it can cause swelling of the lymph glands, abdomen or joints. 

Diagnosing tuberculosis

If you are concerned that you may have TB, see your GP. They will ask you about your symptoms, medical history and travel history. They may then refer you for tests. 

This usually includes a chest X-ray and collection of a sample of phlegm. If you can’t bring up a sample of phlegm when you cough, your doctor may recommend a bronchoscopy. 

A bronchoscopy involves passing a thin, flexible, telescope-like device with a light and a camera on the end (bronchoscope) into your airways to examine your lung tissue and collect a tissue sample (biopsy).

If your doctor suspects you have extrapulmonary TB, you may need an X-ray, CT scan or MRI scan of the affected area. A tissue sample from the affected area will also be collected eg a needle biopsy of the spine for suspected spinal TB or an endoscopy to collect a tissue sample of the bowel for suspected gastrointestinal TB. 

If your tests come back positive for TB, your doctor will recommend that your close contacts, namely people you live with and/or family members you see regularly, are tested for TB. Tests may include a chest X-ray, a skin test called a Mantoux test and/or a blood test.

Mantoux skin test for TB

This skin test will determine whether your body has ever been infected with TB but it cannot determine whether you currently are infected. 

A protein called tuberculin will be injected under your skin. This protein is purified from Mycobacterium tuberculosis but will not make you ill. 

If your body has ever been infected with TB, your immune system will react to the protein by causing a small bump to temporarily appear on your skin where the protein was injected. 

Blood test for TB

The interferon-gamma release assay (IGRA) is a blood test that checks if you have ever been infected with TB. As with the Mantoux skin test, it cannot determine if you are currently infected. 

A sample of your blood will be mixed with proteins purified from Mycobacterium tuberculosis. If your body has ever been infected with TB, the white blood cells in your blood sample will produce a protein called interferon-gamma, which will be detected during the test.

IGRA tests are now more commonly performed rather than the Mantoux skin test.

Treating tuberculosis

If you test positive for TB, whether it is latent or active, you will need treatment. 

While latent TB does not cause any symptoms, around 5–10 cases of latent TB in every 100 will develop into active TB. With treatment, fewer than one in 100 cases of latent TB will develop into active TB. 

Treatment involves taking a combination of drugs for three months in the case of latent TB and for at least six months in the case of active TB.  

The drugs used to treat TB are Isoniazid, Rifampicin, Pyrazinamide and Ethambutol. In most cases, all four antibiotics are taken for the first two months, after which only Rifampicin and Isoniazid are taken for the next four months. However, different combinations may be used depending on your medical history and other medications you may be taking. 

You may need to take medication for up to nine months if you have severe disease ie cavities have formed in your lungs, or if you have extrapulmonary TB. 

If TB has spread to your brain or heart, you may also need to take a course of steroids to reduce the risk of complications due to your infection. 

In rare cases, surgery may be needed to remove a lump formed as a result of tuberculosis (tuberculoma).

Treatment outcomes

Drug treatment for TB is highly successful when taken as directed by your doctor. 

It is important to finish your course of treatment even if your symptoms have resolved. This is because TB may still be present in your body and your symptoms may recur if treatment is stopped partway. 

Moreover, incomplete treatment increases the likelihood that you will develop drug-resistant TB.

Treating drug-resistant TB

More than one in 10 cases of TB in the UK are drug-resistant, which means that it does not respond to treatment with one of the four main drugs used to treat TB in the first instance (first-line treatments). 

In these cases, the drug that is ineffective is removed from the treatment regimen and the treatment is extended to nine months. 

Multidrug-resistant TB refers to TB that is resistant to two of the first-line treatments for TB. These cases of TB are treated with second-line drugs against TB such as Bedaquiline and fluoroquinolones. 

There have also been very rare cases of extensively drug-resistant TB, which are resistant to some of the first-line and second-line drugs against TB. In these cases, specially tailored combinations of drugs are used to clear the infection. 

How to prevent the spread of TB

If you suspect you have TB, wear a mask when you are around other people until you receive your diagnosis. If you receive a diagnosis of pulmonary or glandular TB, you need to self-isolate for 14 days to prevent the spread of TB. 

Once you have started treatment and have been taking your antibiotics for 14 days, you can return to your usual activities. 

Long-term complications of tuberculosis

In severe cases, pulmonary TB can cause cavities – gas-filled spaces – in your lungs. Over time, these cavities can lead to bronchiectasis, that is, abnormal widening of the branches of your airways. This causes persistent breathing problems. 

Other types of TB can also have long-term consequences depending on the tissue or organ affected. For example, spinal TB can destroy the bony discs (vertebrae) of your spine and need surgery to insert metal implants to support your spine. This can reduce the flexibility of your spine and your range of movement.