You can be forgiven for thinking tuberculosis (TB) - or consumption, as it used to be known - has been stamped out in New Zealand. Sadly this is not true.

While the number of new cases in New Zealand continues to decline, according to the latest report from the Institute of Environmental Science and Research the figure is still around 300 per year; nearly one person a day.

As recently as March 2009, a health worker in Wellington has been identified as having the disease, with the Regional Public Health Service undertaking the lengthy task of tracking down all those people who may have been in contact with the person .

The highest rate of new TB infections is in Auckland, with almost half of all diagnosed cases each year.

World Tuberculosis Day 2009 is 24 March, with the theme this year: 'Stop TB'.

What is tuberculosis?

Tuberculosis is an infection caused by a bacterium called Mycobacterium tuberculosis (or rarely by Mycobacterium bovis). There are two distinct states: 

• 1. Active TB disease - where a person is sick, from TB bacteria that are active in their body, and may be infectious to others. There are two categories of active TB disease - a person may have either, or both at the same time:
  - pulmonary TB disease, which affects the lungs 
  - extrapulmonary TB disease, which affects other parts of the body, such as the lymph nodes, kidneys and bones. 
• 2. Latent TB infection (LTBI) - where a person has dormant TB bacteria present in their body, but is not sick, has no symptoms and is not infectious to others.

Above photo, courtesy of Auckland Regional Public Health Service (ARPHS), shows a chest x-ray of someone with active pulmonary TB disease ('white lung' on right).

Signs and symptoms of tuberculosis

Most people who become infected with the TB bacterium - 90% in fact - will never show any sign of TB infection and will never get sick. Their immune systems keep the TB bacteria dormant. This is known as latent tuberculosis infection (LTBI). People with LTBI have no symptoms and this latent form of the infection is not contagious.

Overall just 10% of those infected with the TB bacterium go on to develop active TB disease, sometimes many months or years after being exposed to the bacteria. However, people with weakened immune systems (including the very young and old and those with conditions such as leukaemia or HIV/AIDS) are much more likely to progress to active TB disease.

Active TB disease usually affects the lungs; a condition known as pulmonary TB. When it affects other parts of the body it is called extrapulmonary TB.

People who develop active TB disease often have no symptoms at first, but go on to develop them as the condition progresses. These include:

• tiredness or weakness
• loss of appetite
• loss of weight 
• unexplained fever
• night sweats
• swollen glands (usually in the neck).

Those who have pulmonary TB disease may also have the following symptoms:

• a cough that lasts three weeks or more 
• chest pains 
• shortness of breath
• coughing up blood (this usually occurs very late in the disease).

Anyone who has symptoms of TB disease should see their GP as soon as possible.

How infectious is tuberculosis?

Transmission of infection from people with extrapulmonary TB is very rare. Tuberculosis is almost always passed on to others by someone who has pulmonary TB disease. The bacteria are in the droplets of moisture a person with pulmonary TB expels when he or she coughs, sneezes or speaks.

Tuberculosis is hard to catch, however. Usually only those people who spend many hours in close contact with someone who has the disease may become infected. For example, the disease is more common in homes where many people live in crowded conditions.

Controlling the spread of TB continues to be an issue here and around the world. Poverty, stigma, HIV/AIDS and problems such as people with TB not taking their medication properly all make it harder to prevent the spread. Emerging resistance to the drugs that treat TB further complicates the issue, as drug resistant TB is much more expensive to treat and much more difficult to cure.

What to do if you have had contact with tuberculosis infection

• If you have been in contact with someone who has latent TB infection (LTBI), you will not need to see a doctor, as LTBI is not infectious and cannot be passed on to others.
• If you have been in close contact with someone who had untreated active TB disease at the time of your contact with them, but you are not sick, you may need to be tested to see if you have been infected. Your local public health service is responsible for carrying out this testing, not your GP. 
• If you have been in close contact with someone who had untreated active TB disease at the time of your contact with them and you are sick with symptoms of active TB disease, you should see your GP immediately. If you have not already been contacted by your local public health service, you should contact them to let them know that you think you have been in contact with someone with active TB disease.

Tests for tuberculosis

If you are thought to be at risk of being infected with TB, you may be offered one or more of several tests:

• tuberculin skin test (sometimes called a Mantoux test)
• sputum (spit) test,
• chest x-ray,
• blood test,
• urine test,
• biopsy (for example, if TB infection is suspected in a lymph node).

Treatment for tuberculosis

Tuberculosis can be cured completely with a combination of medicines (special anti-TB antibiotics). Once treatment begins you cease to be infectious within a few weeks and can return to your normal activities among other people.

It takes 6-12 months of anti-TB medication to completely eliminate the bacteria from your body and it is essential that the full course of treatment is taken. If you stop taking your medicine, or don’t take it the way you are advised to, you will quickly become ill and infectious again. You will also greatly increase the risk that the remaining bugs become resistant to the medication you have been taking and it will stop working – in other words you will increase the risk of developing drug-resistant TB, which is much more difficult to cure.

In some circumstances people with TB are given their medicines by directly observed therapy (DOT), where a person (usually a public health nurse) observes the patient taking each dose, to ensure they are taking it properly.

If you have LTBI (dormant TB bacteria in your body) this can also be treated. Treatment of LTBI has been shown to reduce your chances of becoming ill with active TB disease at some time in the future (eg. if your immune system should be weakened by old age or illness).

For more information on tuberculosis, visit Auckland Regional Public Health Service.   

Original material by everybody, reviewed by Dr Cathy Pikholz of Auckland Regional Public Health Service on 17 March 2009.