When microscopic germs like bacteria and viruses enter the body, they can cause infections, leading to illness and disease. Diseases that spread from person to person are said to be infectious and can range in severity depending on the pathogen involved, the mode of transmission, and the individual's immune response. And some infections spread to people from animals or insects but aren't spread to other humans.
That said, do you know which infectious diseases are most common in the US? Find out by clicking through this informative gallery.