Pneumonia
LIFE-THREATENING DISORDERAn acute infection of the lung paren-chyma, pneumonia often impairs gas exchange. The prognosis is generally good for people with normal lungs and adequate host defenses before the onset of pneumonia. However, pneumonia is the seventh leading cause of death in the United States, and in 2003, severe acute respiratory syndrome, a new, deadly type of pneumonia, emerged. (See SARS.)
Causes
Pneumonia can be classified in several ways:
Microbiologic etiology—Pneumonia can be viral, bacterial, fungal, protozoal, mycobacterial, mycoplasmal, or rickettsial in origin.
Location—Bronchopneumonia involves distal airways and alveoli; lobular pneumonia, part of a lobe; and lobar pneumonia, an entire lobe.
Type—Primary pneumonia results from inhalation or aspiration of a pathogen; it includes pneumococcal and viral pneumonia. Secondary pneumonia may follow initial lung damage from a noxious chemical or other insult (superinfection), or may result from hematogenous spread of bacteria from a distant focus. (See Types of pneumonia, pages 650 to 653.)
Predisposing factors
Predisposing factors for bacterial and viral pneumonia include chronic illness and debilitation, cancer (particularly lung cancer), abdominal and thoracic surgery, atelectasis, common colds or other viral respiratory tract infections, chronic respiratory disease (chronic obstructive pulmonary disease [COPD], asthma, bronchiectasis, cystic fibrosis), influenza, smoking, malnutrition, alcoholism, sickle cell disease, tracheostomy, exposure to noxious gases, aspiration, and immunosuppressant therapy.
Predisposing factors for aspiration pneumonia include old age, debilitation, nasogastric (NG) tube feedings, impaired gag reflex, poor oral hygiene, and decreased level of consciousness.
Signs and symptoms
The five cardinal signs and symptoms of early bacterial pneumonia are coughing, sputum production, pleuritic chest pain, shaking chills, and fever. Physical signs vary widely, ranging from diffuse, fine crackles to signs of localized or extensive consolidation and pleural effusion.
SARS
The Centers for Disease Control and Prevention and the World Health Organization are investigating a new disease called severe acute respiratory syndrome (SARS). First reported in China, Vietnam, and Hong Kong, it has since spread to other countries, including the United States and Canada.
SARS commonly begins with a fever greater than 100.4° (38°C), headache, general discomfort and body aches and, in some patients, mild respiratory symptoms. After 2 to 7 days, SARS patients may develop a dry cough and difficulty breathing. The disease, which is highly contagious, is spread by droplets and through contact with contaminated objects. It’s also possible that SARS can be spread more broadly through the air or by other ways that aren’t currently known. A new type of coronavirus is the suspected cause.
Current treatment for SARS is mostly palliative. Antivirals, such as oseltamivir and ribavirin, and steroids in combination with antivirals have been used in patients with SARS, but in the absence of clinically controlled trials, the efficacy of these treatments remains unknown.
Complications include hypoxemia, respiratory failure, pleural effusion, empyema, lung abscess, and bacteremia, with the spread of infection to other parts of the body resulting in meningitis, endocarditis, and pericarditis.
Diagnosis
Clinical features, chest X-ray film showing infiltrates, and sputum smear demonstrating acute inflammatory cells support this diagnosis. Positive blood cultures in patients with pulmonary infiltrates
strongly suggest pneumonia produced by the organisms isolated from the blood cultures.
strongly suggest pneumonia produced by the organisms isolated from the blood cultures.
