INTRODUCTION AND EPIDEMIOLOGY
Pneumonia is an infection of the lung and lower respiratory tract. Globally, pneumonia is the leading cause of death in children less than 5 years of age, with an estimated 120 million cases annually resulting in nearly 1.3 million deaths.1 The greatest burden of disease and mortality occurs in the developing world, and young children under the age of 2 account for 81% of pediatric deaths from pneumonia. The burden of disease in the developed world remains high, with an estimated 2 to 2.6 million cases annually, resulting in nearly a million hospitalizations and significant economic impact.2,3 In the United States, it is the second costliest and fifth most common reason for hospitalization in children.4 This chapter addresses the clinical and radiographic diagnosis of pneumonia, common viral and bacterial causes, evidence-based treatments, and appropriate disposition and follow-up for children seen in the ED. Special mention of unusual microbes, changing patterns of immunization and resistance, and special considerations for children with underlying medical conditions will be highlighted. Clinicians with limited pediatric experience may find the section on the use and interpretation of chest radiographs in children helpful.
Pneumonia results from the invasion and overgrowth of pathogens in the lower respiratory tract.5 Anatomic and mechanical barriers to infection include the nasal hairs and turbinates, cilia, epiglottis, and cough reflex. Humoral immunity is largely mediated by secretory immunoglobulin A. Cellular immunity and phagocytic cells (e.g., alveolar macrophages) further protect against infection. Infectious agents may be inhaled or aspirated directly into the lungs, invade respiratory epithelium and spread contiguously, or, less commonly, reach the lungs hematogenously. Viral inoculation is typically by droplet or fomite (e.g., influenza, respiratory syncytial virus), whereas bacterial pneumonia often follows colonization of the nasopharynx. Infection can result in injury or death of the respiratory epithelium, interstitial inflammation, or alveolar injury. The air space fills with exudative debris, causing atelectasis, impaired oxygenation, and ventilation-perfusion mismatch.
In most cases, the causative agent is never identified. Rapid viral detection via nasopharyngeal or oropharyngeal sampling may identify pathogens, but identification of true bacterial superinfection remains difficult.6 Definitive microbiologic diagnosis requires invasive procedures such as bronchoalveolar lavage, lung puncture, or sampling of pleural effusion for culture or polymerase chain reaction, which are typically unavailable or impractical in the ED.
Viruses are the most commonly detected cause of pneumonia in children, accounting for over 70% of hospitalized cases in the United States.7 Bacterial, atypical, fungal, parasitic, and opportunistic organisms can also cause disease. Infection with Mycobacterium tuberculosis can occur in areas where it is endemic and among children with immunodeficiency. Local and regional epidemiology, individual immunization status, and underlying health problems may influence which pathogens cause pneumonia. Causes of pneumonia vary with age. Patterns of disease can also help guide clinical decisions, as described below.8,9