Clinton has a mild form of pneumonia
Hillary Clinton is believed to have contracted "walking pneumonia."
The illness has been dubbed "walking pneumonia" because it is a mild form of the disease which does not cause her to be bed-ridden.
Pneumonia is caused by bacteria getting into the lungs. At the end of our lungs are clusters of tiny air sacs. Pneumonia causes these to become inflamed and fill up with fluid.
The presidential candidate has community-acquired pneumonia, rather than the more severe form contracted in hospital. Walking pneumonia can affect the sick and healthy. It does not necessarily indicate she is in poor health overall. It is likely to have been picked up on the campaign trail. It is treatable with antibiotics and should clear in a few weeks.