It is estimated that over 2.0 billion people, or one-third of the world's population, are infected with Mycobacterium tuberculosis and there are over 9 million new cases each year. Tuberculosis (TB) is responsible for more deaths than any other infectious agent. In countries such as the UK, the overall annual rate of the disease is about 10 cases/100,000, while in Africa this rate is in excess of 200 cases/100,000. A breakdown of the incidence in different ethnic groups in the UK reflects the rate in the countries of origin. For ethnic minorities who are classified as Black African, Indian subcontinent and Caribbean, the rates per 100,000 are >150, >50 and 20–30 respectively.