This week, presidential candidate Hillary Clinton made news -- not for what she said, but for her health. Her political campaign announced that Clinton had pneumonia after she appeared weak at a public event in New York City. The former Secretary of State left the event suddenly. A video showed several people helping her into a waiting vehicle. So, what is pneumonia? And how does it spread? Simply stated, pneumonia is an infection of the lungs. It is treatable and preventable. However, pneumonia is the leading cause of death among children under five. And it was still responsible for nearly one million deaths in 2015. That information comes from the World Health Organization. Pneumonia most often results from a bacteria called the Streptococcus pneumoniae. But viruses like influenza, and even fungi can cause pneumonia.