Pneumonia is an infection of the lungs. Most patients with pneumonia get better with antibiotic treatment, but some patients develop serious complications and some die of the infection. Pneumonias that people get while living in the community are generally less severe and have better outcomes than pneumonias that people get when they are in the hospital for some other health problem. This difference is due to patient factors, such as underlying illness, and to the types of bacteria that cause pneumonia in these 2 settings. Doctors have recently become aware that pneumonia in patients who are not in the hospital, but have had recent contact with a health care setting, have worse outcomes than patients who have not had such contact. The types of health care situations that seem to matter most are having been hospitalized in recent months, living in a nursing home, receiving kidney dialysis, and receiving intravenous cancer chemotherapy. Researchers call this type of pneumonia health care–associated pneumonia.