Acid-fast bacillus (AFB) refers to a group of bacteria, including the one responsible for tuberculosis (TB), a serious infectious disease primarily affecting the lungs. However, TB can also spread to other parts of the body, such as the brain, spine, and kidneys. The bacteria are known as "acid-fast" because they retain certain dyes even after being washed with acidic solutions, a characteristic used in laboratory tests to identify them.
Tuberculosis is contagious and spreads through the air when an infected person coughs or sneezes, making it important to detect and treat early.