Clinton's doctor said that the presidential hopeful "became overheated and dehydrated" and that "she is now rehydrated and recovering nicely," adding that she was advised to rest and modify her schedule.
Doctors interviewed by The Associated Press said that a case like Clinton's can usually be treated quickly and effectively with antibiotics, adding that the rigors of a presidential campaign, with frequent travel and events in closed spaces attended by large crowds, can make it easier to come down with a lung infection.
For many Americans, getting pneumonia can lead to serious consequences, especially for young children and the elderly.
Globally, pneumonia kills nearly 1 million children younger than 5 years of age each year, but most people seriously affected by pneumonia in the U.S. are older adults.
According to the Centers for Disease Control, more than 53,000 people in the U.S. died from pneumonia in 2013, the most recent year for which statistics are available. People over 65 accounted for more than 45,000 of those deaths.
For U.S. seniors, hospitalization for pneumonia has a greater risk of death compared with any of the other top 10 reasons for hospitalization, according to the American Thoracic Society, a physician's organization that advocates for improving care for lung diseases.
Each year, hospitals in the U.S. admit more than 1.1 million people for pneumonia — making it one of the top causes of hospital stays nationwide. More people were admitted to hospitals for pneumonia in 2010 than for bone fractures, according to the CDC.
The overall death rate for pneumonia in the United States is 16.9 per 100,000 people, and that rate rises dramatically with age, to 27.9 for people from 65 to 74, 98.6 for people 75 to 84 and 414.7 for people 85 or older.
The CDC says you can lower your risk for getting pneumonia by getting vaccinated and doing the following:
Wash your hands regularly.
Clean surfaces that are touched a lot.
Cough or sneeze into a tissue or into your elbow or sleeve.