What is tuberculosis?
Tuberculosis (TB) is a contagious, potentially fatal, infection caused by the bacterium Mycobacterium tuberculosis.
Since the introduction of antibiotics, TB has become less prevalent in Western societies. However, it is still a major public health problem in less developed countries and among people who live in overcrowded and unsanitary conditions.
Although TB can affect any organ in the body, it most commonly affects the lungs, where the infection often first starts.
Active TB versus latent TB
Not everyone with TB becomes sick.
A person can have latent TB, where they have the bacteria in their body, but their immune system protects them from the disease. People with latent TB are not infectious, but the disease can flare up later in life – and become active TB, which is infectious.
People with active TB also carry the bacteria, but they show symptoms of TB such as those below. People with active TB (TB disease) are infectious and should see a doctor immediately, if they are not already under the care of a doctor. In active TB, the bacteria multiply and attack various organs of the body.
How is TB spread?
A person with active TB can spread the bacteria through coughing, sneezing or laughing — or even talking. Tiny droplets are released into the air where they can be inhaled by others. However, it is fairly difficult for a healthy person to become infected with TB without prolonged close contact with someone who is infected.
A person with latent TB infection will have no symptoms. If you’ve got active TB you may notice some or all of the following symptoms:
- feeling tired all the time;
- persistent cough (cough that lasts for 3 weeks or more);
- coughing up phlegm or blood;
- chest pain;
- loss of appetite;
- weight loss;
- fever and/or chills; and
- night sweats.
These symptoms commonly also occur with other types of lung disease so it is important to see a doctor to have your condition thoroughly investigated. A person with active TB disease may not necessarily feel very ill in the early stages, and may have a cough only from time to time. If you think you have been exposed to TB, see your doctor straight away.
Who is most at risk of TB?
Anyone can catch TB. However, there seem to be groups of people who are more likely to be at higher risk for active disease. These include:
- newly arrived immigrants and refugees from areas where the disease is prevalent, who caught the infection before they arrived in Australia;
- people in close contact with those who have TB;
- people with weakened immune systems;
- people who use tobacco, drink heavily or use intravenous drugs; and
- people who are poorly nourished.
In Australia there are approximately 1200 new cases of TB diagnosed each year — the majority are in people not born in Australia.
Tests for TB
If you have been exposed to the disease or you are showing symptoms, your doctor may do a Mantoux skin test.
You will be given an injection of a small amount of protein derived from TB bacteria into the skin of your forearm, and this will be examined about 2–3 days later. If the injection site is red or swollen, it indicates current or past infection. However, sometimes the Mantoux test can give a false-negative result (the test suggests you don’t have TB when you do) or a false-positive result (the test suggests you do have TB when you don’t). People who have been vaccinated against TB may show a positive result.
TB blood tests
Blood tests (called interferon-gamma release assays – IGRAs) are also available for the detection of tuberculosis infection. These tests measure the response of your immune system to the TB bacteria. They are not affected by previous tuberculosis vaccination, but can give false-negative results.
Chest X-ray or CT scan
If you have a positive Mantoux skin test or TB blood test, your doctor may suggest a chest X-ray or chest CT scan to look for signs of TB infection in your lungs.
Fluid or tissue sample
To confirm a diagnosis of TB, doctors need to identify the TB bacteria in a body fluid, such as sputum (phlegm) or urine, or body tissue removed for biopsy.
Active TB is treated with a number of different antibiotics taken together over a significant period — usually at least 6 months. It is very important to take all doses of the antibiotics for the entire period they are prescribed, to stop the TB bacteria becoming resistant to the medicines.
Fortunately, most cases of TB in Australia are responsive to the antibiotics. Properly taken, TB medicines for fully susceptible bacteria provide an almost 100 per cent cure rate.
To prevent spread of this serious infection, people with active TB may need to be isolated until they are no longer infectious, generally after 2 to 4 weeks of treatment.
Active tuberculosis that is resistant to the antibiotics usually used to treat TB requires a combination of several antibiotics over an extended period – about 20 to 30 months.
Treating latent TB reduces the risk of the person developing active TB. Usually, just one antibiotic is taken, for 6–12 months.
Doctors often recommend treatment if you have latent TB and you:
- have HIV infection;
- are in close contact with someone with active TB;
- were recently infected with TB;
- are a child, adolescent or are younger than 30 years with no known TB contact;
- need to take medicines that suppress your immune system; or
- have a long-term health condition such as kidney failure or diabetes.
Your doctor or specialist will monitor your TB treatment and may modify it depending on the results of tests.
Antibiotic side effects can occur, including liver damage. When longer treatment durations are needed to treat drug-resistant TB, there is a higher chance of serious side effects.
Complications of TB
A TB infection may spread to and affect the reproductive organs of both men and women. It can spread to the bones and joints, causing back pain and symptoms of inflammation and pain in the joints.
TB can also affect the skin, bowel, adrenal glands and heart, and even the brain, leading to tuberculous meningitis. Tuberculous meningitis is a life-threatening condition that can lead to coma and brain damage.
Another life-threatening type of TB is miliary tuberculosis, where a large number of bacteria are released into the bloodstream and spread around the body. Symptoms include fever, chills, weakness, weight loss and difficulty in breathing. If the bacteria spread to the bone marrow, blood abnormalities can occur.
There is a vaccine available against tuberculosis, known as the BCG (bacille Calmette-Guerin) vaccine. This vaccine is not routinely recommended for the general population in Australia, and it does not offer complete protection against TB. However, certain groups who may be at increased risk of TB may benefit from vaccination, including children who will be travelling to countries with a high TB incidence, and certain healthcare workers.
2. World Health Organization (WHO). Tuberculosis (updated Oct 2014). http://www.who.int/mediacentre/factsheets/fs104/en/ (accessed Nov 2014).
3. Australian Government Department of Health and Ageing. The Australian Immunisation Handbook, 10th Edition 2013. 4.20 Tuberculosis (updated 17 Jan 2014). http://www.immunise.health.gov.au/internet/immunise/publishing.nsf/Content/handbook10-4-20 (accessed Nov 2014).
4. Centers for Disease Control and Prevention (CDC). Tuberculosis: general information (updated 28 Oct 2011). http://www.cdc.gov/tb/publications/factsheets/general/tb.htm (accessed Nov 2014).
5. Coulter C. Tuberculosis testing. Aust Fam Physician. 2012 Jul: 41 (7): 489-92.