Hillary Clinton has pneumonia: How dangerous is pneumonia? How do you get it?

Hillary Clinton became ill Sunday at the ceremony remembering the victims of the terror attacks on 9/11, leaving the event early, then seeming to stumble and slump as she was attempting to get into a van.

A while later, Clinton, 68, came out from her daughter Chelsea’s near-by Manhattan apartment, telling those assembled there she was “feeling great.” Later on Sunday, however, Clinton’s campaign released a statement saying the Democratic nominee for president had been diagnosed with pneumonia last Friday, and her episode on Sunday was due to the illness and getting overheated.

Here’s a quick look at pneumonia, a disease that each year sends some 1 million Americans to doctors seeking treatment.

What is Pneumonia?

Pneumonia is an infection of the lungs. It’s more often a mild disease, but it can be more severe and, in some cases, deadly. Pneumonia happens when the lungs – or one of the lobes of the lungs – become infected and begin to leak fluid and shed dead cells. The liquid and cells clog the lungs and makes it increasingly difficult to breathe.

It’s a common disease, with more than 1 million Americans a year seeking medical attention for the condition.

What causes pneumonia?

Pneumonia is caused by either a virus, a bacterial infection, fungus or a parasite. A person is more susceptible to pneumonia if they are elderly, have a weakened or compromised immune system, are a cigarette smoker, are an alcoholic or are suffering for some other illness. Constantly being in close quarters and coming into contact with many people, as presidential candidates do,  increase your odds of contracting the disease.

Bacterial vs. viral

The two types of pneumonia most often seen are viral and bacterial.

Bacterial pneumonia happens when bacteria infects the lungs. For bacterial pneumonia, an antibiotic is prescribed.

In the case of viral pneumonia, a virus causes the disease, and treatment is aimed more at relieving symptoms. Sometimes antivirals are prescribed, especially if the flu is the cause of the pneumonia and it is caught early.  Occasionally, antibiotics will be given if the lungs are weakened and there's a chance you could contract bacterial pneumonia.

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What are the symptoms of pneumonia?

Symptoms of pneumonia can be mild  or severe. Here are some of them:

• A  cough which produces sputum (mucus) that may be a rusty orange  color or green.

• Fever

• Feeling “short of breath”

• Shaking and chills

• Chest pain that feels worse when you cough or inhale

• Racing heartbeat

• Feeling tired or weak

• Nausea and vomiting

• Diarrhea

• Older adults may show signs of  confusion

"Walking pneumonia"

Clinton was described as having "walking pneumonia" in several reports. When you have pneumonia, have mild symptoms, and are not confined to a hospital, your doctor may call what you have "walking pneumonia."

Why does pneumonia make you so sick?

Fluid and pus gets stuck in the air sacs and makes it hard for the lungs to get oxygen into the blood. Without that oxygen, the cells do not work as they should. When they don't work as they should you will have trouble breathing and you can have trouble moving and walking and even trouble forming thoughts.

How long  does it take to get over pneumonia?

With the proper medication and rest, it generally takes about two weeks to heal from pneumonia. However, doctors say, you may feel tired or weak for a month or more.

Spreading pneumonia to others

You can spread pneumonia to others as long as you are contagious – which can be from several days to a week, depending on which type of pneumonia you have. Once treated with antibiotics, the contagious period ends within 24 hours or so.