In 2003 tuberculosis, often abbreviated to 'TB', affected 8.7 million people. Most of these people lived in Asia and Africa, a small proportion were in Europe and the Americas.
The World Health Organisation reports that someone with open tuberculosis would infect 10 to 15 people a year. So when a certain number of people are infected it is very hard to stop it spreading further. Tuberculosis bacilli are spread through the air when someone sneezes or coughs.
In the past 50 years drugs have been developed to treat tuberculosis. The disease has since developed strains that are resistant to those drugs.