Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis. TB may affect many body organs, but it primarily affects the lungs. It is spread through the air from person to person through lung secretions such as sputum (spit or phlegm) or aerosols released by coughing, sneezing, laughing, or breathing. Most of those who become infected with M. tuberculosis manage to confine the mycobacteria to a few cells in their body, where they stay alive in an inactive form. This inactive or latent TB infection does not make the patient sick or infectious and, in most cases, it does not progress to cause active tuberculosis.
However, some patients - especially those with damaged or compromised immune systems - may proceed directly from initial TB infection to active tuberculosis. And in another ~10%-15% of those with latent TB infection, the mycobacteria will later be reactivated and begin to multiply - leading to active progressive tuberculosis disease.
TB has been a leading cause of death worldwide for thousands of years. In the days before the discovery of antibiotics it was called consumption, and those who contracted it were put into long-term hospitals called sanatoriums for the rest of their lives. TB first became a statutorily notifiable disease in the UK in 1913; with almost 120,000 cases in that year. The number of new cases fell progressively until the mid 1980s, however numbers started to rise again in the early 1990s. Overall total numbers of TB cases has declined by 11.6% in the last two years. However, worldwide, TB is still the leading cause of death due to infection - killing more than 3 million people a year.
In developed countries such as the USA or the UK, the majority of these cases were among those living in overcrowded or confined conditions such as prisons, nursing homes, and schools. The most vulnerable were those who had poor health care or had diseases and conditions that weakened their immune systems, such as: the homeless, alcoholics, intravenous drug users, those with HIV or AIDS, and those with chronic kidney or liver diseases. Often these new cases were multi-drug resistant (MDR), making them more difficult to treat. The revised UK immunisation programme on TB is to target infants in areas where the incidence of TB is greater than 40 cases / 100000, or have parents or grandparents who were born in countries with such an incidence.