Tuberculosis is a serious disease that mainly affects the lungs. The germs that cause tuberculosis are a type of bacteria. Tuberculosis can be spread when a sick person coughs, sneezes, or sings. This can send tiny droplets containing germs into the air. Another person can then inhale the droplets, and the germs enter the lungs. Tuberculosis spreads easily in places where people gather in crowds or live in crowded conditions. People with HIV/AIDS and others with weakened immune systems are at higher risk of developing tuberculosis than people with typical immune systems.