Because the bacteria that cause tuberculosis are transmitted through the air, the disease can be quite contagious. However, it is nearly impossible to catch TB simply by passing an infected person on the street. To be at risk, you must be exposed to the organisms constantly, by living or working in close quarters with someone who has the active disease. Even then, because the bacteria generally stay dormant after they invade the body; only 10% of people infected with TB will ever come down with the active disease. The remaining 90% will show no signs of infection, nor will they be able to spread the disease to others. Dormant infections can eventually become active, though, so even people without symptoms should receive medical treatment.
Once widespread, TB became relatively rare with the help of antibiotics developed in the 1950s. Today, however, a new and highly resistant form has emerged, creating a public-health hazard in many large cities worldwide. If you have TB -- in its active or dormant state -- you must seek medical treatment.
Tuberculosis is generally caused by exposure to microscopic airborne droplets containing the bacterium Mycobacterium tuberculosis. The disease is almost never transmitted through clothes, bedding or other personal items. Because most people with TB exhale only a few of these germs with each breath, you can contract the disease only if you are exposed to an infected person for a long time. If you spend eight hours a day for six months, or 24 hours a day for two months, with someone with an active case of TB, you have a 50% chance of getting infected
