Hillary Clinton's Pneumonia Diagnosis: What You Should Know

— -- Hillary Clinton's pneumonia diagnosis has drawn attention to a disease that leads to 53,282 deaths in the U.S. every year. But pneumonia is actually a broad disease category that encompasses a variety of illnesses.

Pneumonia simply means lung infection, and the cause of that infection and resulting illness can be from a variety of factors. Pneumonia leads to 1.1 million hospitalizations every year, according to the U.S. Centers for Disease Control and Prevention.

Clinton's spokesman said on CNN today that the presidential candidate is "not contagious." This would indicate she probably does not have certain kinds of viral pneumonia. But without further information it is still unclear what kind of pneumonia Clinton has contracted.

Here is an overview of the different kinds of pneumonia.

Bacterial Pneumonia

A variety of bacteria can lead to lung infections, with the most common type being Streptococcus pneumoniae. This kind of pneumonia can occur after an infection such as cold or the flu, or it can occur on its own.

Staphylococcus aureus -- the bacteria that causes staph infections -- can also cause lung infections. It usually occurs in people with weakened immune systems, such as children or hospitalized patients, but can occur in anyone.

Atypical pneumonia can happen when common bacteria called Mycoplasma pneumoniae, which live in the mouth, end up in the lungs. The bacteria can grow slowly, leading to a hacking cough, but not severe symptoms. This disease used to be called "walking pneumonia" because many people would not realize they had the disease and often people do not need bed rest. Approximately between one to 10 of every 50 cases of community-acquired pneumonia (lung infections developed outside of a hospital) in the United States is caused by M. pneumoniae, according to the CDC.

Symptoms can include chest pain when you breathe or cough, fever, fatigue, or in people over age 65 a lowering of normal body temperature.

Viral Pneumonia

Viruses can also cause serious lung infections. Pneumonia after contracting the influenza virus can be dangerous. The influenza virus weakens the immune system, making it easier for dangerous bacteria to cause infection.

While influenza or flu may be the virus people are most aware of, other viral illnesses, including respiratory syncytial virus (RSV) and the human parainfluenza virus can cause pneumonia.

Pneumonia from certain viruses, including the herpes virus and adenoviruses, are generally rare for healthy adults but they can affect people with weakened immune systems or children.

Fungal Pneumonia

In rare cases, some people can contract pneumonia from fungi. In these cases, the person usually has a severely weakened immune system and can develop an infectious from certain kinds of fungus.

One kind of fungus is Pneumocystis jirovecii, which can live in the lungs for long periods of time, according to the CDC. Infection with this form of fungus used to be especially dangerous for people with HIV/AIDS, though new medications have helped diminish the likelihood of dangerous infection.