Pneumonia is sometimes classified according to the cause of pneumonia:
Community-acquired pneumonia : This takes place in the course of your daily life while carrying out daily life activities.
Hospital-acquired (nosocomial) pneumonia : This kind of pneumonia is common with people who are hospitalizedThe chances increases if the patient is on a mechanical ventilator. This type of pneumonia can be extremely serious, especially for old people, young children and people with chronic obstructive pulmonary diseases (COPD) or HIV/AIDS.
Aspiration pneumonia : This kind of pneumonia occurs when foreign substance is inhaled (aspirated) into your lungs — most often when the contents of your stomach enter lungs after vomiting. This commonly happens when a brain injury or other condition affects your normal gag reflex.
Pneumonia caused by opportunistic organisms : This type of pneumonia strikes people with compromised immune systems.Organisms that aren’t harmful for healthy people can be extremely dangerous for people with AIDS, organ transplantation and other conditions that impair the immune system. For example, P. carinii pneumonia almost never occurs in otherwise healthy people.
Emerging pathogens : Outbreaks of the H5N1 influenza (bird flu) virus and severe acute respiratory syndrome (SARS) can also cause pneumonia infection.