Pneumonia Pneumonia is defined as inﬂammation of the distal lung that includes terminal airways, alveolar spaces, and the interstitium. Pneumonia may have multiple causes, including viral and bacterial infections or aspiration. Aspiration pneumonia is usually the result of depressed awareness commonly associated with the use of drugs and alcohol or anesthesia. Viral pneumonias are caused by multiple infectious agents, including inﬂuenza A or B, parainﬂuenza virus, or respiratory syncytial virus. Most viral syndromes are spread by aerosolization associated with coughing, sneezing, and even conversation. Incubation is short, requiring only 1 to 3 days before the acute onset of fever, chills, headache, fatigue, and myalgias. Symptom intensity is directly related to intensity of the host febrile reaction. Pneumonia develops in only 1% of patients who have a viral syndrome, but mortality rates may reach 30% in immunocompromised individuals and the elderly. An additional risk is the development of secondary bacterial pneumonias after the initial viral insult. These infections are more common in elderly patients and may explain the high fatality in this group (8). Staphylococcal pneumonias, which often arise from a previous viral infection, are extremely lethal regardless of patient age. The best treatment for viral pneumonia is prevention by immunization. Treatment is supportive and consists mostly of administration of antipyretics and ﬂuids.
Bacterial pneumonia is classified as either community acquired or nosocomial, and in many cases the classification determines prognosis and antibiotic therapy. Risk factors that contribute to mortality are chronic cardiopulmonary diseases, alcoholism, diabetes, renal failure, malignancy, and malnutrition. Prognostic features associated with poor outcome include greater than two lobe involvement, respiratory rate greater than 30 breaths per minute on presentation, severe hypoxemia (<60 mm Hg on room air), hypoalbuminemia, and septicemia. Pneumonia is a common cause of adult respiratory distress syndrome (ARDS), with a mortality rate between 50% and 70% (9,10).
Signs and symptoms of pneumonia vary depending on the infecting organism and the patient’s immune status. In typical pneumonias, the usual presentation is a patient with high fever, rigors, productive cough, chills, and pleuritic chest pain. Chest radiography often will show infiltrates (11). The following agents, listed in decreasing order, cause two-thirds of all bacterial pneumonias: Streptococcus pneumoniae, Haemophilus inﬂuenza, Klebsiella pneumoniae, gram-negative organisms, and anaerobic bacteria. Atypical pneumonias are more insidious in onset than typical pneumonias. Patients have moderate fever without the characteristic rigors and chills. Additional symptoms include a nonproductive cough, headache, myalgias, and mild leukocytosis. Chest radiography reveals bronchopneumonia with a diffuse interstitial pattern; characteristically, the patient does not appear to be as ill as the x-ray suggests. Common causes of atypical pneumonia include viruses, Mycoplasma pneumoniae, Legionella pneumophila, Chlamydia pneumoniae (also called the TWAR agent), and other rare agents.