Porth's Essentials of Pathophysiology, 4e

545

Respiratory Tract Infections, Neoplasms, and Childhood Disorders

C h a p t e r 2 2

Alveolar lumen

A

Interstitium

A

B

FIGURE 22-4. Distribution of lung involvement in (A) lobar pneumonia and (B) bronchopneumonia.

pneumoniae, Chlamydia species, and viruses, some- times called atypical agents. Common viral causes of community-acquired pneumonia include the influenza virus, respiratory syncytial virus, adenovirus, and para- influenza virus. The methods used in the diagnosis of community- acquired pneumonia depend on age, coexisting health problems, and the severity of illness. In persons younger than 65 years of age and without coexisting disease, the diagnosis usually is based on history and physical examination, chest radiographs, and knowledge of the microorganisms currently causing infections in the com- munity. Sputum specimens may be obtained for staining procedures and culture. Blood cultures may be done for persons requiring hospitalization. Treatment involves the use of appropriate antibiotic therapy. Empiric antibiotic therapy, based on knowledge regarding an antibiotic’s spectrum of action and abil- ity to penetrate bronchopulmonary secretions, often is used for persons with community-acquired pneumonia who do not require hospitalization. Hospitalization and more intensive care may be required depending on the person’s age, preexisting health status, and severity of the infection. Hospital-Acquired Pneumonia. Hospital-acquired, or nosocomial, pneumonia is defined as a lower respi- ratory tract infection that was not present or incubat- ing on admission to the hospital. Usually, infections occurring 48 hours or more after admission are con- sidered hospital acquired. 14,24,25 Persons requiring intu- bation and mechanical ventilation are particularly at risk, as are those with compromised immune function, chronic lung disease, and airway instrumentation, such as endotracheal intubation or tracheotomy. Ventilator- associated pneumonia is pneumonia that develops in mechanically ventilated patients more than 48 hours after intubation.

B FIGURE 22-3. Location of inflammatory processes in (A) typical and (B) atypical forms of pneumonia.

the alveolar septum and the interstitium of the lung (Fig. 22-3B). They produce less striking symptoms and physical findings than bacterial pneumonia; there is a lack of alveolar infiltration and purulent sputum, leu- kocytosis, and lobar consolidation on the radiograph. Acute bacterial pneumonias can be classified as lobar pneumonia or bronchopneumonia, based on their ana- tomic pattern of distribution. 14 In general, lobar pneu- monia refers to consolidation of a part or all of a lung lobe, and bronchopneumonia signifies a patchy consoli- dation involving more than one lobe (Fig. 22-4). Community-AcquiredPneumonia. Theterm community- acquired pneumonia is used to describe infections from organisms found in the community rather than in the hospital or nursing home. It is defined as an infection that begins outside the hospital or is diagnosed within 48 hours after admission to the hospital in a person who has not resided in a long-term care facility for 14 days or more before admission. 20–23 Community-acquired pneumonia may be further categorized according to risk of mortality and need for hospitalization based on age, presence of coexisting disease, and severity of illness, using physical examination, laboratory, and radiologic findings. Community-acquired pneumonia may be either bac- terial or viral. 14,20–23 The most common cause of infec- tion in all categories is S. pneumoniae. Other common pathogens include H. influenzae, S. aureus, and gram- negative bacilli. Less common agents are Mycoplasma