Most cases of pediatric pneumonia develop from inhalation of infective bacteria or viruses. The clinical presentation, likely etiologic agents, severity of illness, and disposition, vary with age. In the neonate, group B Streptococci, gram-negative bacteria, and Listeria monocytogenes, are important pathogens. In the 1 to 3 month old age group, infants may be afebrile with pneumonitis syndrome secondary to Chlamydia trachomatis, respiratory syncytial virus (RSV), other respiratory viruses, and Bordetella pertussis. In the 1 to 24 month age group, mild to moderate pneumonia can be caused by respiratory viruses as well as Streptococcus pneumoniae, Haemophilus influenzae, and Mycoplasma pneumoniae. Although viral pathogens dominate during years 2 to 5, the above bacterial pathogens are common. By the sixth year through 18 years of age, influenza virus A or B and adenovirus are common. At any age, severe pneumonia may be caused by S aureus, S pneumoniae, M pneumoniae, H influenzae B, and group A streptococci.
Clinical features of pneumonia are quite variable. In addition to the age of the patient, factors that affect the clinical presentation of pediatric pneumonia include the specific respiratory pathogen, the severity of the disease, and underlying illnesses. Tachypnea is the most commonly physical sign; other signs and symptoms of pneumonia include respiratory distress, rales, or decreased breath sounds. The absence of these findings in a well appearing child makes pneumonia unlikely. Neonates and young infants with pneumonia may present with a sepsis syndrome, and signs and symptoms can be nonspecific: fever or hypothermia, apnea, tachypnea, poor feeding, vomiting, diarrhea, lethargy, grunting, bradycardia, and shock. In older children, signs and symptoms of pneumonia are similar to adults and include fever, abnormal lung sounds, cough, and pleuritic chest pain. Possible associated findings may include headache, malaise, wheezing, rhinitis, conjunctivitis, pharyngitis, and rash. The clinical manifestations of bacterial and viral pneumonias overlap, making the clinical distinction problematic. Lower lobe pneumonias may cause significant abdominal pain and distention mimicking acute appendicitis.
Though chest radiography is the gold standard for the diagnosis of pneumonia, clinical diagnosis is reasonable: fever, cough, and focal findings on the lung exam along with tachypnea and possibly hypoxemia comprise the classic clinical diagnostic criteria. If obtained, chest radiography may demonstrate a segmental or lobar infiltrate suggestive of bacterial pneumonia; diffuse air-space disease, hyperinflation, peribronchial thickening or cuffing and atelectasis seen with viral and atypical pathogens; or pleural fluid suggestive of empyema. However, there is overlap in the radiographic appearance of bacterial and viral pneumonias, making this distinction problematic at times. In children, the thymus can be mistaken for a mediastinal mass or lobar pneumonia and this normal finding must be differentiated from pulmonary pathology (Fig. 71-1).
Arrows indicate a normal thymus. Rotation, apparent from the location of the heart, trachea, and clavicles, makes this thymus appear to be far right of midline. (Courtesy of ...