Causes of pneumonia in immunocompromised persons include gram-negative enteric bacteria, mycobacteria (M. avium complex), fungi (aspergillosis), viruses (CMV), and Pneumocystis jiroveci (carinii). Pneumonia in patients with cystic fibrosis usually is caused by Staphylococcus aureus in infancy and Pseudomonas aeruginosa or Burkholderia cepacia in older patients.
Immunizations have had a great impact on the incidence of pneumonia caused by pertussis, diphtheria, measles, Haemophilus influenza type b, and S. pneumoniae. Where used, bacille Calmette-Guerin (BCG) for tuberculosis also has had an impact. An estimated 2 million deaths in developing countries are due to acute respiratory tract infections annually. Risk factors for lower respiratory tract infections include gastroesophageal reflux, neurologic impairment (aspiration), immunocompromised states, anatomic abnormalities of the respiratory tract, residence in residential care facilities, and hospitalization, especially in an intensive care unit.
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Cough Wheezing Hemoptysis Chest Pain Abdominal Pain Failure to Thrive Acidemia
Age is a determinant in the clinical manifestations of pneumonia. Neonates may have fever or hypoxia only, with subtle or absent physical examination findings (see Chapter 65). With a young infant, apnea may be the first sign of pneumonia. Fever, chills, tachypnea, cough, malaise, pleuritic chest pain, retractions, and apprehension, because of difficulty breathing or shortness of breath, are common in older infants and children. Physical examination findings cannot reliably distinguish viral and bacterial pneumonias, but complete physical examination may help identify other foci of disease or associated findings to suggest an etiology.
In general viral pneumonias are associated more often with cough, wheezing, or stridor; fever is less prominent than with bacterial pneumonia. Mucosal congestion and upper airway inflammation suggest a viral infection. Bacterial pneumonias typically are associated with higher fever, chills, cough, dyspnea, and auscultatory findings of lung consolidation. Atypical pneumonia in young infants is characterized by tachypnea, cough, crackles on auscultation, and concomitant (chlamydial) conjunctivitis (infants) may be present. Other signs of respiratory distress include nasal flaring, intercostal and subcostal retractions, and grunting.
Asymmetry or shallow breathing may be due to splinting from pain. Hyperexpansion, common in asthma but also frequently accompanying viral lower respiratory infections, may cause a low diaphragm or liver. Poor diaphragmatic excursion may indicate hyperexpanded lungs or an inability for expansion due to a large consolidation or effusion. Dullness to percussion may be due to lobar or segmental infiltrates or pleural fluid. Auscultation may be normal in early or very focal pneumonia, but the presence of localized crackles, rhonchi, and wheezes may help one detect and locate pneumonia. Distant breath sounds may indicate a large, poorly ventilated area of consolidation or pleural fluid.