Tuberculosis

Tuberculosis (TB) is an infectious disease caused by the Mycobacterium tuberculosis bacteria. It is spread from person to person through airborne droplets. The bacteria usually attack the lungs, but TB bacteria can attack any part of the body such as the kidney, spine, and brain. If not treated properly, TB disease can be fatal. TB is strongly associated with poverty, overcrowding and malnutrition and it is estimated that a third of the world's population is affected.

Symptoms

Usually there are no symptoms with TB infection initially. It may take years for infected individuals to develop symptoms. People usually cannot spread the disease until these symptoms are present. Treatment with medication can prevent the asymptomatic infection from developing into active disease.

Symptoms include:

  • a bad cough that lasts 3 weeks or more fever night sweats weight loss
  • coughing up blood pain in the chest
  • weakness and fatigue no appetite

    Travellers at highest risk of contracting TB are:

    • Health care and aid workers in countries with a high incidence of TB
    • Expatriate workers and their families living in countries with a high incidence of TB
    • Those spending three months or more in countries with a high incidence of TB, particularly if living in close contact with the local population
    • Anyone with a compromised immune system

    TB is more likely to be contracted in overcrowded living conditions, poor ventilation and close personal contact with an infected person. For someone who has a normal immune system it usually takes repeated exposure over a long period before TB infection occurs. High risk areas include Africa, Latin America, Southern Asia, South-East Asia, the Middle East and the former states of the Soviet Union.

    There are 2 main methods of preventing symptomatic TB disease.

    The first is BCG vaccination.

    • In WA this can ONLY be done at the Perth Chest Clinic. Its effectiveness is very variable but it generally only gives 30-50% protection for adults against developing active lung disease. It is more effective in children and may prevent TB from spreading to other parts of the body, which is much more common and serious in children. BCG is usually only recommended for ;
    • Children under the age of 6yo travelling for more than 3 months to countries with higher incidence of TB (more than 50 cases per 100,000 people)
    • Health care and aid workers in areas with high incidence of TB.

    BCG vaccinations may cause an abscess at the site of injection which can lead to an unsightly scar if not looked after properly. BCG is usually only given once as boosters do not appreciably increase the amount of protection.

    A negative TB test is required prior to receiving a BCG. This can be done at the travel clinic.

    The second method of preventing TB disease is by doing a pre-travel and post-travel Mantoux skin test or QuantiFERON-TB Gold in Tube test (QIFN).

    These tests when done pre-travel gives a baseline reading of your body's current reactivity to TB. This is repeated on return if the traveller has symptoms of TB or has had high risk exposure while away.

    Health authorities in Australia and in the USA prefer to use the Mantoux testing and early treatment, whereas in Europe some authorities recommend travelers have a BCG. Certainly in developing countries where TB is a significant health problem, BCG vaccination is recommended for all children as treatment may not be available.

    The Mantoux or tuberculin skin test (TST) is a test used to detect whether or not a person has been exposed to or infected by the tuberculosis bacteria..

    Why is it done?

    A Mantoux is generally carried out as

    • An investigation for suspected TB
    • A pre-requisite for BCG vaccination
    • A baseline for employment in a health care facility or prior to prolonged travel to a high risk TB area

    How is a Mantoux skin test done?

    A Mantoux test is done by injecting a small amount of a sterile protein solution (prepared from killed TB bacteria) into the skin of the forearm. A small wheal may form at the injection site. The result is read 72 hours at a second appointment after the injection and the area should not be scratched or rubbed during this time. The test may need to be repeated at this stage as a second reading is sometimes more accurate.

    What does the result mean?

    Positive result

    If the lump is above a certain size the result of the test is positive. It means that you may have been infected with the TB bacteria. It does not mean you have TB disease. When you are infected with TB bacteria you are not infectious, you can not pass the bacteria onto other people. You are not sick, but at some stage you may develop TB disease. If you are told your Mantoux is positive you may be asked to have a chest x-ray.

    Negative result

    If the lump is below a certain size the result of the test is negative. Usually this means that you have not been infected with TB bacteria. However if your contact with TB was very recent you may need to have the test repeated in 8 - 12 weeks. A false negative can occur if you have had a recent viral infection (e.g. measles, mumps, chicken pox etc) , immunosuppressed or have had a recent live vaccination (e.g. MMR or Yellow Fever vaccination)

    Are there any side effects from the test?

    The side effects are mainly related to the size of the reaction and include local swelling, itchiness and discolouration which may take a few weeks to clear. Very strong reactions are uncommon and may be associated with a painful swelling of several centimetres in size, blistering, or ulceration and red streaks in the arm. They heal eventually with negligible scarring.

    QuantiFERON-TB GOLD in Tube Test

    A QIFN is a simple blood test. However is it not suitable when specimens cannot reach the laboratory within an appropriate time i.e. rural and remote W.A. In W.A. specimens need to reach the laboratory within 16 hours of collection. It can be advantageous to have a QIFN when someone has had a positive Mantoux in the past or is unable to attend the second appointment to have their Mantoux test read.

    © 2013, Travel Medicine Centre Perth