In light of Hillary Clinton's diagnosis, here's everything you need to know about pneumonia
Pneumonia is one of the most common illnesses in the U.S.
The lung infection puts about 1 million adults in the hospital every year, and it can get pretty serious -- about 50,000 die from it.
Hillary Clinton's doctor confirmed Sunday that the Democratic presidential candidate is being treated for the disease. It's unclear how she got infected.
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