Tuberculosis (abbreviated as TB for Tubercle Bacillus) is a common and highly infectious disease caused by the Mycobacterium tuberculosis bacteria. It most commonly affects the lungs but can also attack the central nervous system, lymphatic system, kidneys, bones, joints and the skin.

Worldwide it kills up to 3 million people per year.

Once infected the disease may not cause sickness for years when it stays in its latent form, but then may emerge in its active form. Only 1 out of ten healthy people infected will become ill with TB. If the person is otherwise compromised (HIV) 1 in 10 TB infected people will become ill with active TB per year.

A person gets TB by breathing the TB bacteria into his/her lungs. It is spread into the air by a person ill with TB. The infective droplet nucleus is very small, measuring 5 micrometers or less, and may contain approximately 1-10 bacilli. 5-200 inhaled bacilli are usually necessary for infection. Once inhaled the bacilli are deposited into the respiratory bronchiole or alveoli.

Sometimes the immune system is able to kill the TB bacteria. If the person's immune system is unable to kill the bacteria, then this person has TB infection. In its latent form it cannot be spread to others. The greatest risk of the disease advancing into its active form is within 2 years of initial infection.

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