Frequency
The true incidence of aspiration pneumonia is unknown, because many cases of community-acquired and nosocomial pneumonia may be due to unrecognized aspiration. Also, few studies have been designed that distinguish between aspiration pneumonia and aspiration pneumonitis. However, several studies suggest that 5-15% of the estimated 4.5 million cases of community-acquired pneumonia in the United States per year result from aspiration pneumonia.
Aspiration pneumonia occurs most commonly in hospitalized and chronically institutionalized adults, particularly those with preexisting stroke, seizures, or other conditions that predispose to aspiration. In light of an increasing elderly population with many comorbid conditions predisposing to aspiration, the incidence of aspiration pneumonia among patients admitted to US hospitals is likely to rise. In addition, approximately 10% of patients who are hospitalized after drug overdoses will have an aspiration pneumonitis. Internationally, aspiration pneumonia is considered a common disease, but no statistics are available.
Mortality/Morbidity
The mortality associated with aspiration pneumonia mimics that of community-acquired pneumonia: approximately 1% in the outpatient setting and up to 25% in those requiring hospitalization. This mortality range depends on complications of the disease.
The mortality rate for severe chemical pneumonitis (Mendelson syndrome) can be up to 70%.
Without treatment, aspiration pneumonia is associated with a high incidence of cavitation and abscess formation, in comparison to community-acquired pneumonia. Other complications of both aspiration pneumonia and pneumonitis include empyema, acute respiratory distress syndrome, and respiratory failure. Aspiration pneumonitis can rapidly progress to respiratory failure.
Symptoms
Symptoms of aspiration pneumonia include: Fever, fatigue, cough (with greenish or foul-smelling sputum or sputum containing pus or blood), chest pain, shortness of breath, bluish discoloration of the skin caused by lack of oxygen, rapid pulse (heart rate) and wheezing. Additional symptoms that may be associated with this disease include excessive sweating, difficulty swallowing and breath odor.
Diagnosis
The clinical presentation in both aspiration pneumonitis and pneumonia ranges from mildly ill and ambulating to critically ill with signs and symptoms of septic shock and/or respiratory failure. There are no specific diagnostic tests for aspiration pneumonia. Clinicians must surmise this diagnosis when a patient presents with risk factors and radiographic evidence of an infiltrate suggestive of aspiration pneumonia. The location of the infiltrate on chest radiograph depends on the position of the patient when the aspiration occurred.
The diagnosis is usually based on new findings of hypoxemia, pulmonary infiltrates in gravity-dependent lung regions, fever, and leukocytosis after an observed or suspected episode of vomiting or regurgitation in a patient at risk for aspiration. Most affected patients are febrile and tachypneic. Rales are present in about two thirds of patients, and cough, wheezing, or cyanosis is seen in one third.
Most patients with aspiration pneumonia are treated in the absence of a specific microbiologic diagnosis. The main barriers to establishing such a diagnosis are the difficulty in obtaining specimens of deep respiratory tract secretions without contamination by oral flora and the limited laboratory capacity for isolation of anaerobic organisms. Expectorated sputum is not a valid specimen for anaerobic culture because it is invariably contaminated with oral flora. However, sputum should be examined by Gram stain and culture for aerobic pathogens.
Physical Examination
Physical examination findings vary, depending on the severity of the disease, the presence of complications and host factors. Patients with aspiration pneumonitis secondary to seizure, head trauma, or drug overdose should be inspected for signs related to these processes. Both aspiration pneumonia and pneumonitis can present with the following:
- Fever or hypothermia
- Tachypnea
- Tachycardia
- Decreased breath sounds
- Dullness to percussion over areas of consolidation
- Rales
- Egophony and pectoriloquy
- Decreased breath sounds
- Pleural friction rub
- Altered mental status
- Hypoxemia Hypotension (in septic shock)
In addition, patients may exhibit signs associated with the underlying disease that led to their aspiration.