Nosocomial Pneumonia



Lung infection in a hospitalized patient is termed nosocomial pneumonia. It occurs in 1 to 5 per cent of all hospitalized patients and is re­sponsible for 15 per cent of hospital deaths. Up to 60 per cent of ICU patients may develop pneu­monia, and up to half of these die. More than 60 per cent of nosocomial pneumonias are due to gram-negative bacilli (GNB), and the main source of organisms is the patient’s own oropharynx. Subsequent entry into the lung is probably achieved by aspiration. In mechanically venti­lated patients, direct entry is further facilitated by the presence of an endotracheal or tracheostomy tube. Organisms reach the oropharynx by a number of routes, including fecal contamination of the hands of the patient or attendant, or more com­monly by retrograde movement from the stomach to the oropharynx. A less frequent source is the surrounding environment, such as sinks, food, and flowers. Antibiotics reduce the normal inhib­itory flora and predispose to GNB colonization. There is a marked difference in the rate of oro­pharyngeal colonization with GNB in healthy sub­jects (2 to 18 per cent) compared to medical ICU patients (50 per cent) and ICU patients with a pri­mary respiratory diagnosis (100 per cent), possi­bly related to the increased adherence of bacilli to the regional epithelium in seriously ill patients. Colonization also confounds the etiological di­agnosis, because expectorated or aspirated trach­eobronchial secretions are usually contaminated by the colonizing upper airway organisms. In this setting, precise bacteriological diagnosis is par­ticularly perplexing, and culture of secretions, with the inevitable recovery of a’ diverse array of potential pathogens, is likely to be misleading and to result in patient mismanagement. Differentia­tion of colonization from infection should be based on an overall evaluation of the patient, tak­ing into account fever, leukocytosis, the presence of purulent secretions, and a new or progressive infiltrate on chest x-ray, although the value of these findings is lessened in patients with un­derlying lung disease. Blood cultures, when pos­itive (which is rare), are helpful. If a precise eti­ological diagnosis is desired, invasive measures are usually required, such as transtracheal aspi­ration, transthoracic aspiration, or fiberoptic bronchoscopy employing a plugged telescoping catheter brush technique. In patients receiving multiple antibiotics even this is often misleading. Commonly, antibiotic therapy, including cover­age for gram-positive and gram-negative organ­isms, is instituted on an empirical basis.