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Why some people die from pneumonia and others don't
Once called "the old person's friend" because it can kill elderly people enfeebled by disease, pneumonia is in the news because of Hillary Clinton's diagnosis. Who gets it, and why do some of them die, while others recover quickly? - photo by Jennifer Graham
It killed entertainer Bob Hope and abolitionist Harriet Tubman, and contributed to the death of George Washington, the first president, and William Henry Harrison, the first president to die in office.

But most people diagnosed with pneumonia, like Hillary Clinton was, respond well to treatments, and for some, the condition is little more than fever and a cough that doesn't want to go away.

Once called "the old man's friend" because it can kill elderly people enfeebled by disease, more than 53,000 people in the U.S. died from pneumonia in 2013, according to the Centers for Disease Control and Prevention.

About 61 percent of Americans over the age of 65 have been vaccinated for it, however, and the death rate, roughly 17 per 100,000 Americans, is needlessly high, the CDC says.

"Pneumonia infections can often be prevented and can usually be treated," the agency says on its website.

A lung infection caused by viruses, bacteria and fungi, pneumonia's symptoms are coughing, fever and having trouble breathing.

At age 68, Clinton falls into a high-risk group: people older than 65. Others at higher risk of contracting pneumonia include smokers, children younger than 5, and people with other health conditions such as heart disease, diabetes or asthma.

Many people develop pneumonia after having the flu. (Harrison, the ninth president, developed it after a bad cold he caught soon after his inauguration in 1841.)

It occurs when germs get into a person's lungs because the immune system is weakened, the nose and airways didn't properly filter out the invaders, or the person was exposed to an especially large or strong onslaught of germs, according to the American Lung Association.

The air sacs of the lungs become inflamed and fill with fluid.

Most healthy people recover within three weeks, but in severe cases, the infection spreads and interferes with oxygen reaching the bloodstream. In extreme cases that go untreated, pneumonia can kill within hours, PBS has reported.

Some people have speculated that Clinton may have what is colloquially known "walking pneumonia," a milder version that allows the person to go about everyday activities, NBC News reported.

Mild cases can be treated with rest, fluids and over-the-counter anti-inflammatory drugs, such as ibuprofen.

But depending on whether the infection is viral or bacterial, and the age and overall condition of the person, hospitalization may be required, and pneumonia may persist for a month or more, the Lung Association says.

The type of pneumonia determines whether it's contagious or not, Fox News reported. "Bacterial infections are not contagious, while viral infections are," Nicole Kwan reported for Fox.

Dr. Robert Kotloff, chairman of pulmonary medicine at the Cleveland Clinic, told Kwan that from what he knows, he believes Clinton's pneumonia to be bacterial.

There are more serious diagnoses that require hospitalization and, in some cases, care in an intensive care unit, but it doesnt sound like this particular situation fits those criteria, Kotloff said.

Regardless of how quickly Clinton recovers, her case has brought attention to an illness that is responsible for about 15 percent of deaths of young children around the world, mostly in South Asia and sub-Sarahan Africa, according to the World Health Organization.

Mark your calendar: World Pneumonia Day is Nov. 12, four days after Election Day in the U.S.
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