The alphabet soup of pneumonia: CAP, HAP, HCAP, NHAP, and VAP.

The classification of pneumonia is increasingly complex as the patient population becomes more diverse. More and more patients are identified with pneumonia attributed to multidrug-resistant (MDR) bacteria, occurring both in the hospital setting and outside of the hospital. This is likely related to the expanding pool of patients at risk for colonization with MDR bacteria. These expanding patient populations include individuals residing in nonhospital health care facilities (e.g., long-term nursing facilities, assisted living environments, rehabilitation centers), patients undergoing outpatient procedures or therapies (hemodialysis, wound care, infusion therapy), patients who have been recently discharged from the hospital setting, and those with significant underlying immunosuppression. Patients exposed to these nonhospital risks who develop pneumonia have traditionally been categorized as having community-acquired pneumonia (CAP). However, the new designation for pneumonia acquired in these environments is healthcare-associated pneumonia (HCAP). Additionally, some authors have categorized patients in nursing homes as developing nursing home-acquired pneumonia (NHAP) because there may be distinct epidemiological associations with this infection. Although HCAP is currently treated with the same protocols as CAP in many hospitals, recent evidence indicates that HCAP differs from CAP with respect to pathogens and prognosis, and in fact, more closely resembles hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) requiring broader empirical antimicrobial therapy than CAP.