Abstract:
TB infection of humans has been recognised for many thousands of years. The disease exists in all countries in the world and is endemic in most of the poorer countries. TB is estimated to currently infect around one third of the current world population. Most of those infected carry the organism with no symptoms, called latent tuberculosis infection (LTBI). Of the LTBI approximately 5-10% will reactivate and develop clinical disease sometime over their life course. Most new cases occur in the developing countries and infection is usually acquired in childhood. The Bacille Calmette-Guérin (BCG) vaccines have been in use for over 80 years, routinely since the 1960s, in almost all countries except the United States (US) and the Netherlands, and have been given to over four billion people.