Microbiological Classification of Pneumonia

Pneumonia classified according to the probable origin of infection into community acquired pneumonia or nosocomial (hospital acquired) pneumonia (Wilkinson and Woodhead, 2004).

a) Community acquired pneumonia
Community-acquired pneumonia (CAP) is defined as an infection of the alveolar or gas-exchanging portions of the lungs occurring outside the hospital, with clinical symptoms accompanied by the presence of an infiltrate in the chest radiograph (Lippi et.al., 2011).
Most bacterial infections result from aspiration of nasopharyngeal organisms, although inhalation of infected droplets from other patients, from animals, or from environmental sources , less commonly, hematogenous spread to the lung (Baltzer et.al., 2006).

b) Nosocomial pneumonia
The spectrum of nosocomial pneumonia can include hospital acquired pneumonia (HAP), health care associated pneumonia (HCAP), and ventilator associated pneumonia (VAP) (Jevtic, 2009).

Hospital acquired pneumonia is defined of pneumonia occuring at least 48 hours after hospital admission (Kollef and Micek, 2005).
It may result as a direct result of surgery (postoperative and aspiration pneumonia) but is more often a result of major co morbidity, for example chronic obstructive pulmonary disease (COPD) or general debility in elderly. Two to five percent of hospital admission are complicated by development of this condition (Yarnell, 2007).
Ventilator associated pneumonia is defined as nosocomial Pneumonia in patients receiving mechanical ventilation via an endotracheal tube that develops 48 hours or more after initiation of ventilation ( curley et. al., 2006).
Ventilator associated pneumonia is the most frequent infection in intensive care
units (ICU) and has a high mortality and morbidity rate (Bouza et.al., 2011). It occurs in 8% to 28% of patient receiving mechanical ventilation in ICU (Wu et.al., 2011).
Heath care associated pneumonia [HCAP] :- This category includes patients who a] receive home nursing, intravenous antibiotics, or wound care; b] patients who reside in nursing homes or long-term care facilities; c] patients who have been hospitalized for ≥ 2 days in the past 90 days; d] patients who have received dialysis or IV therapy at a hospital-based clinic in the past 30 days (Kronish and Dorr, 2008).