The setting in which pneumonia develops is often important to diagnosis and treatment, as it correlates to which pathogens are likely suspects, which mechanisms are likely, which antibiotics are likely to work or fail, and which complications can be expected based on the patient's health status.
Community-acquired pneumonia (CAP) is acquired in the community, outside of health care facilities. Compared with health care–associated pneumonia, it is less likely to involve multidrug-resistant bacteria. Although the latter are no longer rare in CAP, they are still less likely.
HCAP, MCAP, HAP, VAP, and NHAP
Health care–associated pneumonia (HCAP) is any pneumonia associated with any health care, whether in a hospital, outpatient clinic, nursing home care, or home care. The latter two settings could be viewed as community settings except that they are usually correlated with health care via proximity to, and interaction with, others who have recently visited health care facilities, such as nurses, doctors, and nursing home neighbors.
Medical care–associated pneumonia (MCAP) is sometimes considered synonymous with HCAP and is sometimes viewed as a subset of it.
Hospital-acquired pneumonia is acquired in a hospital and as such is likely to involve hospital-acquired infections, with higher risk of multidrug-resistant pathogens. Also, because hospital patients are often ill (which is why they are present in the hospital), comorbidities are an issue.
Ventilator-associated pneumonia occurs in people breathing with the help of mechanical ventilation. Like any medical device, ventilators involve some risk of infection because of how difficult it is to prevent bacteria from colonizing the internal parts and surfaces, even with diligent cleaning. People who need venitlators typically are rather ill to begin with, so a superimposed pneumonia is not always easily managed. Immunodeficiency may be involved because of poor nutritional status and whichever disorders are comorbid.
Nursing home–acquired pneumonia is acquired in nursing home care. A nursing home is a place where even if a resident has not visited a hospital recently, neighbors have, and visiting health professionals have. This, coupled with the comorbidities that typically are associated with advanced age, is why NHAP is viewed as a form of HCAP and has a higher chance of resembling HAP in its causes and features than CAP generally does.