ETIOLOGY AND PATHOGENESIS OF PNEUMONIA IN CHILDREN

Abstract

 Pneumonia is a leading cause of morbidity and mortality among children worldwide, particularly in children under five years of age. It represents a complex clinical syndrome characterized by inflammation of the lung parenchyma, resulting from diverse infectious agents and a range of host immune responses. The etiology of pediatric pneumonia is multifactorial, including bacterial, viral, fungal, and, less commonly, parasitic pathogens. Streptococcus pneumoniae, Haemophilus influenzae type b, and respiratory syncytial virus (RSV) are the most frequently identified causative agents in different pediatric age groups. Understanding the pathogenesis of pneumonia requires an integrated view of microbial virulence factors, host immune mechanisms, and environmental determinants. In children, the immaturity of both innate and adaptive immunity plays a crucial role in susceptibility and disease severity. Pulmonary defense mechanisms, such as mucociliary clearance, alveolar macrophages, and local antibody responses, may be insufficient in young children, facilitating microbial invasion and inflammatory damage. Excessive or dysregulated immune responses can contribute to tissue injury, hypoxemia, and complications such as pleural effusion or sepsis. Environmental factors, including malnutrition, air pollution, and inadequate vaccination, further exacerbate risk. This article provides a comprehensive review of the etiological agents of pediatric pneumonia and the mechanisms underlying its pathogenesis. By examining the interplay between infectious agents and the developing immune system, it highlights opportunities for early prevention, timely diagnosis, and effective therapeutic interventions, which are essential to reducing the global burden of childhood pneumonia.