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INTRODUCTION AND EPIDEMIOLOGY
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Pneumonia is an infection of the lung and lower respiratory tract, below the level of the larynx. Globally, pneumonia is a leading cause of morbidity and mortality, 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. Although survival in industrialized countries is better than in the developing world, the burden of disease remains high, with an estimated 2 to 2.6 million cases annually, resulting in nearly a million hospitalizations.2 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. Wherever possible, you will see special mention of unusual microbes, changing patterns of immunization and resistance, and special considerations for children with underlying medical conditions. If you have limited pediatric experience, you may find the section on the use and interpretation of chest radiographs in children helpful.
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Pneumonia occurs through invasion of the lower respiratory tract by pathogens. 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, whereas 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 exudate and WBCs, which disrupt oxygenation and cause air space collapse, with eventual ventilation-perfusion mismatch.
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In most cases, the causative agent is never known. Definitive microbiologic diagnosis requires invasive procedures such as bronchial lavage or sampling of pleural effusion for culture, which are unavailable or impractical in the ED.
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Overall, viruses predominate in younger children, although 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, so one should take into account local and regional epidemiology, individual immunization status, and underlying health problems that may influence which pathogens are likely. The types and causes of pneumonia vary considerably according to the age of the child; a few general rules and specific exceptions are described below.3,4
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CLINICAL FEATURES AND ETIOLOGY
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The cardinal symptoms of lower respiratory tract infection include cough, fever, tachypnea, and respiratory distress. However, signs and symptoms vary by age and specific causative agents. Both age-based etiology and pathogen-specific clinical patterns ...