18.02.1 Introduction

Tuberculosis, commonly known as TB, is caused by Mycobacteria tuberculosis, which is a very slow-growing bacterium. Tuberculosis mainly affects the lungs, and infection is spread by inhalation of infectious aerosols. In the developing world, 7 million new cases of TB are reported annually, and 3 million people die of this disease annually. In Australia, the TB notification rates are 5/100,000, which means that 5 people out of every 100,000 have TB. TB is a disease of low social status and overcrowding, with the overcrowding promoting the spread of the TB. In Australia, the people who are most likely to have TB are the refugees and migrants from countries with a high-incidence of TB, people with alcohol or drug dependence, the homeless, HIV-(human immunodeficiency virus)-infected people, and indigenous people.

Unfortunately, there is no single drug that is effective in the treatment of TB, partly because it is so slowly growing, and partly because resistance has developed to the drugs which used to be used to treat TB. One of the other problems with treating mycobacterial infections is that the mycobacteria have a more complex cell wall structure, which is less permeable to many chemicals. The mycobacteria are, therefore, resistant to many of the commonly used antibacterial agents. The first-line treatment for TB is a combination of ethambutol, isoniazid, rifampicin and pyrazinamide for two months. This is followed by isoniazid and rifampicin for a further minimum of four months. Isoniazid and ethambutol are bactericidal/bacteriostatic and effective against the actively dividing Mycobacteria. Rifampicin and pyrazinamide have a sterilising (killing) action against the Mycobacteria when they are present but not dividing (i.e. dormant cells).