Tuberculosis is caused by bacteria that mainly attack the lungs, although other parts of the body also can be affected. The bacteria is spread through tiny droplets in the air, when an infected person coughs, sneezes or even just talks or laughs and someone else breathes in the bacteria. But even if someone gets infected, most of the time their immune system is strong enough to keep them from getting sick. Instead, they have what is called latent TB, meaning they have TB germs in their bodies but they are not sick and are not contagious. They could still develop active TB, even years later, if their immune system weakens. Most cases of TB can be treated and usually cured with medication, although some strains are drug-resistant. The disease can be fatal if untreated, however.