TB facts from the World Health Organisation

Someone in the world is newly infected with TB bacilli every second and one third of the world's population is now infected with TB.

However only five to ten percent of people who are infected with TB bacilli (but not infected with HIV) become sick or infectious at some time during their life.

But HIV and TB are a lethal combination and it is the leading cause of death among people who are HIV-positive.

Only people who are sick with TB in their lungs are infectious. When infectious people cough, sneeze, talk or spit, they propel TB germs, known as bacilli, into the air.

A person needs only to inhale a small number of these to be infected.

Left untreated, each person with active TB disease will infect on average between ten and 15 people every year.

But people infected with TB bacilli will not necessarily become sick with the disease.

The immune system walls off the TB bacilli which, protected by a thick waxy coat, can lie dormant for years.

When someone's immune system is weakened, the chances of becoming sick are greater.

Africa has the highest TB deaths while Asia has the most cases.

By nation, India has the most cases, followed by China, Indonesia, South Africa and Nigeria, according to the 2006 WHO report based on data from 202 countries and territories.

TB strains that are resistant to all major anti-TB drugs have emerged, necessitating up to two years of chemotherapy.