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28 Mar 2017

Explainer: what is TB and am I at risk of getting it in Australia

This article was written by Associate Professor Justin Denholm for The Conversation.

Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis. It most commonly causes pneumonia - a lung infection. Sick people will experience cough, fever, sweats and weight loss, usually over weeks to months.

TB can also cause disease in other parts of the body. The most severe types affect the brain (TB meningitis) or spread through the bloodstream (disseminated TB).

Like other bacterial infections, tuberculosis is curable with antibiotics. It is a slow-growing bacteria, so long courses of several antibiotics are needed for effective treatment. Usually, this means a six month course of two to four antibiotics each day.

There are many strains of TB, and some drug resistant TB take much longer to finish treatment. Worldwide, there are growing problems with multi-drug resistant (MDR) TB. This is defined as being resistant to the two main antibiotics (isoniazid and rifampicin) and cases are not common in Australia (about 2% of all cases).

Tuberculosis is still a common disease in many parts of the world. There were more than 10 million cases and 1.4 million deaths from the disease in 2015. The risk of contracting the disease varies a great deal globally, with countries including India, South Africa and Indonesia being most affected.

Am I at risk?

In Australia, there are around 1200 to 1300 cases of tuberculosis each year, which means we are among the lowest-risk countries in the world. Because of Australia’s low rate of TB and high health-care standards, we have been identified by the World Health Organization as one of the countries best placed to eliminate TB entirely.

People who were born and grew up in Australia are very unlikely to get TB, unless they have close contact with a sick person.

The people most at risk of TB in Australia are those who have spent their early years of life in countries with high rates of the disease, and have contracted it without knowing. Even many years after leaving, people can still be at risk of getting sick with TB.

People who are sick with TB pneumonia can infect others through coughing. But TB is much less contagious than influenza or other viral infections. People who spent long periods of close contact, especially young children living in a household with the sick person, are most at risk of contracting TB.

People with serious immune problems, such as HIV infection or cancer chemotherapy, are also at higher risk of becoming sick if they are exposed.

If a person does have close contact with someone with TB, they can breathe in TB and become infected. Most people with a normal immune system will not become sick themselves, but instead keep TB bacteria in a “sleeping” state called latent TB infection.

People with a latent infection may never become sick, but will have a chance of developing active TB at some point in their lives. People with latent TB will not feel sick, and cannot infect others, but can be identified with blood or skin tests. Antibiotic treatment is available for people with latent TB which can greatly reduce the risk of becoming sick in future.

When cases of TB happen in Australia, state and territory public health programs make sure those who are sick receive appropriate treatment, including antibiotics and hospital care. Tuberculosis treatment is provided free of charge in Australia for anyone who needs it.

TB programs will also investigate those who may have been in contact with the contagious person. These programs will arrange testing for community members who might be at risk, and suggest treatment to prevent those found to have been infected from becoming sick.

Isn’t there a TB vaccine?

The Bacille Calmette-Guerin vaccine (BCG) for TB has been available for about 100 years, and is still one of the most widely used vaccines in the world. It is especially effective in preventing severe TB in young children, although much less effective in adults.

In Australia, the BCG vaccine was given routinely until the early 1980s, when it was removed from the vaccine schedule because falling TB rates made it unnecessary. Australian guidelines still recommend some groups of people get the vaccine.

This includes children younger than five who will be travelling overseas to countries with high rates of TB, and Aboriginal and Torres Strait Islander children living in TB-risk areas.

Australians who travel frequently, including to countries such as Vietnam, Indonesia and Papua New Guinea where TB is much more common, are fortunately at very low risk of catching TB overseas, and no pre-travel vaccines are needed.

People at very high risk of TB exposure, like those going to work in healthcare in countries with high TB rates or those on immune suppressing medication, may need special advice and should talk about risk with their doctors prior to travel.

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