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Pneumonia in children: Epidemiology, pathogenesis, and etiology

William J Barson, MD
Section Editor
Sheldon L Kaplan, MD
Deputy Editor
Mary M Torchia, MD


Childhood pneumonia is an important cause of morbidity in the developed world, and morbidity and mortality in the developing world. The epidemiology, microbiology, and pathogenesis of pneumonia in children will be reviewed here. The clinical features, diagnosis, and treatment of pneumonia in children are discussed separately, as is pneumonia in neonates (<28 days of age). (See "Community-acquired pneumonia in children: Clinical features and diagnosis" and "Community-acquired pneumonia in children: Outpatient treatment" and "Pneumonia in children: Inpatient treatment" and "Neonatal pneumonia".)


The terms pneumonia and pneumonitis strictly represent any inflammatory condition involving the lungs, which include the visceral pleura, connective tissue, airways, alveoli, and vascular structures. Lower respiratory tract infection (LRTI) is frequently used interchangeably to include bronchitis, bronchiolitis, and pneumonia, or any combination of the three. For the purposes of this review, pneumonia will be defined as a condition typically associated with fever, respiratory symptoms, and evidence of parenchymal involvement, either by physical examination or the presence of infiltrates on chest radiography. Bronchiolitis is discussed separately. (See "Bronchiolitis in infants and children: Clinical features and diagnosis", section on 'Clinical features'.)


Incidence — The World Health Organization (WHO) estimates there are 156 million cases of pneumonia each year in children younger than five years, with as many as 20 million cases severe enough to require hospital admission [1]. In the developed world, the annual incidence of pneumonia is estimated to be 33 per 10,000 in children younger than five years and 14.5 per 10,000 in children 0 to 16 years [2].

Approximately one-half of children younger than five years of age with community-acquired pneumonia (CAP) require hospitalization [3]. Hospitalization rates for pneumonia (all causes) among children younger than two years in the United States decreased after introduction of the pneumococcal conjugate vaccine to the routine childhood immunization schedule in 2000 (from 12 to 14 per 1000 population to 8 to 10 per 1000 population) (figure 1) [4].

Mortality — The mortality rate in developed countries is low (<1 per 1000 per year) [5,6]. In developing countries, respiratory tract infections are not only more prevalent but more severe, accounting for more than 2 million deaths annually; pneumonia is the number one killer of children in these societies [1,7].


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