Epidemiology of hospital-acquired pneumonia.

Nosocomial pneumonia may account for a relatively small percent of all hospital-acquired infections, but it is associated with the highest mortality of all nosocomial infections. Risk factors include increasing age, thoracoabdominal surgery, presence of chronic lung disease, duration in hospital, immunosuppressive therapy, continuous ventilatory support, and means of payment. Among patients dying in the hospital, a nosocomial pneumonia was present in 40% and was causally related or contributed to death in 60% of nosocomially infected patients. Gram-negative bacilli, Staphylococcus aureus, and viruses are the most common etiologic agents. Changes in T lymphocytes with aging, alterations in the physiologic and anatomic defenses from trauma, disease, or aging and lack of appropriate infection control barriers predispose to development of pneumonia. Extra hospital charges of approximately $1,000 and four to five additional hospital days result. Analysis of pertinent epidemiologic data require understanding of clinical definition of pneumonia, laboratory methods used to analyze respiratory secretions, and methods of comparing added charges and length of stay.