Family doctor

What is tuberculosis?

Tuberculosis, or TB, is an infectious disease caused by either Mycobacterium tuberculosis or Mycobacterium bovis. Because these germs are so similar, the infections they cause are given the one name - tuberculosis.

Why is tuberculosis so important?

Tuberculosis is extremely difficult to eradicate. This organism was infecting man thousands of years before the birth of Christ. Currently, about one third of the world's population is infected with tuberculosis. Each year millions of people die from tuberculosis world wide.

Tuberculosis germs are difficult to eradicate because they can lie dormant in the body's tissues for many years before becoming active and causing the disease known as tuberculosis.

How does TB spread?

You catch TB in the same way that you catch a cold - TB spreads from one person to another by the infected person coughing, and thus expelling TB germs into the air. Another person nearby can then inhale these germs and become infected.

Tuberculosis is only infectious if the disease is in the lungs, or if a TB skin sore remains uncovered. Infectious TB lung disease is common. TB skin sores are uncommon, usually occurring when an infected TB lymph gland " bursts".

Areas of the body which have tuberculosis but are not in direct contact with the air are not infectious.

Although TB spreads by breathing in air from someone with infectious/active TB, it generally takes many hours of exposure (and often days) for a previously non-infected person to become infected. Thus, most people who breathe in TB germs don't get TB disease.

Who gets tuberculosis?

Anyone can get TB.

People who are especially at risk of developing tuberculosis fall into the following categories:

People whose resistance to infection is impaired: for instance, the elderly and the new born, people with serious chronic illness, those on steroid tablet treatment, those with HIV/Aids, with insulin-dependant diabetes, alcoholics and others. If people in these categories have dormant TB germs in their body, they are at risk of active TB developing.

People who are exposed to a high dose of TB germs: the large number of organisms is able to overcome the body's own defences, enabling full-blown tuberculosis to develop.

People who have had active TB disease which has healed without treatment: many people coming to New Zealand from countries which have a high incidence of both TB and poverty are found on a chest x-ray to have had previous TB, to their surprise.

It can be seen that getting TB depends only on exposure to the germs, which are "caught" from another person. Ideas that TB is "hereditary" - that is, "in the genes" - are old-fashioned, incorrect ideas. Another idea, present in some cultures, that you must be "bad" to have TB is also totally incorrect. Anyone can get TB.

What is the difference between TB infection and TB disease?

This point is often confusing to people inside and outside the health profession.

Tuberculosis infection - this means a person has TB organisms in their body, but there is no evidence that the germs are active, growing or causing damage to body tissues.

TB disease - this term refers to the fact that there is at least one area of the body where TB germs are growing and causing tissue damage. The term "active tuberculosis" refers to TB disease. The most common places in the body where TB occurs are the lungs and in lymph glands.

What are the symptoms of tuberculosis?

Often people have TB and feel perfectly well. In its early stages, TB is a silent condition.

As the disease increases, symptoms may occur. Common symptoms include tiredness, loss of weight and fever. There may also be drenching night sweats, such that the bedclothes and pyjamas are soaked and need changing during the night. A cough which goes on for more than three weeks should also raise at least the thought of tuberculosis. Sometimes, coughing up blood may occur. Often though, TB is first suspected when changes are seen on the chest x-ray.

If someone is unwell and they are concerned they might have TB, they should see their doctor and ask for a chest x-ray and sputum check for TB.

How is TB diagnosed?

TB can only be diagnosed with certainty if TB germs are found - for instance, in phlegm the person has coughed up, in urine, or in tissue which has been removed from the body, such as a lymph gland. If tuberculosis is a possibility and sputum is being produced, it should definitely be examined for TB germs.

Sometimes tuberculosis is suspected from a chest x-ray appearance in people who are otherwise perfectly well. When no sputum can be produced there are different tests to try and obtain a definite answer.

1. Bronchoscopy is the most common test in this situation - this involves using local anaesthetic to allow the thin, flexible plastic "telescope" (the bronchoscope) to be passed through the person's nose or mouth into their breathing tubes without discomfort. The areas of lung which look abnormal on chest x-ray are rinsed with fluid, which is then collected through the bronchoscope and sent to the laboratory for TB testing.

2. Induced sputum - this is a new test which is not generally available. The test must be carried out in a room fitted with negative-pressure air conditioning. Briefly, the person inhales a salt-water mist for about 20 minutes. This causes some coughing and mucus production, and a specimen can then be collected and sent to the laboratory for TB tests.

3. A Mantoux skin test is a simple skin test that involves injecting a tiny volume of test liquid under the skin of the forearm. About 48-72 hours later the area must be examined for swelling or blistering: these changes indicate a positive test. Unfortunately, the interpretation of the Mantoux result can be difficult, as we will see.

A positive test: changes are seen or felt at the injection site. A positive reaction may occur as an immune response to previous BCG vaccination. (BCG vaccination is given to prevent TB). In people who have not been vaccinated, a positive reaction means either there are now, or have been, TB germs in the body. It does not distinguish whether the condition is active or healed.

A negative test: no reaction at the injection site usually means the person has not been infected with TB germs. However, no reaction occurs occasionally in people who do have TB infection or TB disease. Steroid tablet treatment and major illnesses can produce a false negative Mantoux test in a person who has TB.

Confused? The Mantoux test is difficult to understand - it often needs a TB specialist to sort out what the reaction means.

How is TB treated?

TB can be cured, using modern treatment. TB treatment involves using three or four special TB-antibiotics. They are tablets and capsules, which are normally given before and after breakfast. The four main medicines that kill TB germs are: rifampicin, isoniazid, pyrazinamide and ethambutol.

Most other infections in the body only require a week or two of antibiotic treatment for cure. Unfortunately, TB medications have to be taken for many months to cure this disease. Every dose of medicine must be taken. The treatment usually has to go on for a minimum of 6 months, and may need to continue for longer.

Sometimes people decide that, because they feel so well, and they have already taken TB treatment for weeks or months, that they don't want to continue any longer. Although this is understandable, it is a disaster if the full course of treatment isn't taken. Stopping treatment early or not taking the treatment at regular times allows the TB germs to get used to the medicine, so that the medicine stops being effective. Incorrect taking of treatment is the most common cause of drug resistant TB germs. These resistant germs may be very difficult, or even impossible, to cure. On the other hand, if TB treatment is taken properly, cure is guaranteed in almost 100% of cases.

Side effects can occur with some of the TB medicines, but these problems can be solved. If you have problems taking TB treatment, let the doctors and nurses who are looking after you know exactly whatthe problem is and almost always a solution that suits you will be found. Blood tests will be required during the first couple of months of treatment, but only occasionally after that. Be prepared for your urine and tears (and sometimes other body fluids) to turn an orange-red colour, if you are taking rifampicin and Rifinah. This colour change occurs because of the presence of the rifampicin in the body fluids. Testing of vision needs to be done periodically if ethambutol is used.

Is TB always infectious?

People who have pulmonary tuberculosis - that is, TB disease in their lungs - and have TB germs in their phlegm are infectious.

Weeping TB skin ulcers (sores) occasionally develop, and they can be infectious - but not if they are covered with a proper dressing.

TB in the kidneys, bone, brain or other areas inside the body which are not in contact with air are not infectious.

Anyone with pulmonary tuberculosis should take great care to cover their nose and mouth when they cough or sneeze.

If tests show that a person has infectious pulmonary tuberculosis, they need to be "isolated" until the condition is no longer infectious. Isolation means keeping out of public places and restricting contact with people to those who have already been exposed, such as family members. People with infectious pulmonary TB should also wear a special face mask when they are in contact with other people. During this phase of the illness, it is permissible to walk around in the open air, such as in a park, but not in a shopping centre, church, or other place where people get together.

With treatment, most people become non-infectious within a few weeks. After that, the person with TB is not a risk to their family, friends or others. Normal activities can be safely resumed.

What is DOT?

These initials stand for "directly observed therapy". Directly observed therapy has been the single most important improvement in tuberculosis care world wide in the last 5-10 years. DOT is strongly recommended now because it gives certainty that every dose of medication will be taken, thereby making certain that the person with tuberculosis will be cured.

DOT is also an advantage in that doses of medication are only given twice or three times per week (depending on the TB specialist's recommendation). This advantage is offset by the fact that more tablets need to be taken on those days.

Key points to remember about TB:

• TB can be cured
• Every dose of TB medication must be taken - this prevents drug resistant germs developing and makes certain that cure will be achieved
• Cover your mouth and nose with tissues when you cough
• Anyone at all can get TB: having TB doesn't mean the person is bad in some way.