ABSTRACT

Invasion of lung tissue by pathogenic microorganisms is relatively common during the newborn period because of the immaturity and naiveté of the immune system, including specific pulmonary defenses, and the fragility of the mechanical barriers provided by skin and mucous membranes. Premature birth increases the susceptibility but, as with all infections, host factors are but one part of the story. Other important concerns are the characteristics and dose of the microorganisms encountered, the balance struck between colonization and invasion and the existence of abnormal portals of entry such as endotracheal tubes. Pneumonia is an exceptionally serious condition for the newborn and is responsible for the deaths of some two million infants per year worldwide.256 In the developing world, pneumonia occurring during the neonatal period carries a ten times greater mortality than when it occurs at any other time in infancy.33 Pneumonia is particularly dangerous when respiratory reserve is already limited by conditions such as RDS (p. 245), CLD (p. 399) or congenital anomalies. Neonatal pneumonia may be an isolated focal infection but is commonly part of a more widespread infective illness.221 Definition and ascertainment of cause is generally more difficult with pneumonia than with other focal infections. This is partly because non-infective pulmonary pathology is so common in babies, and often impossible to distinguish radiologically, and partly because the isolation of microorganisms from respiratory secretions is not synonymous with pneumonia in the same way that microorganisms in the CSF are synonymous with meningitis. Indeed, bacteria can be found in the

of babies who show no histological evidence of pneumonia.35,37,38,329 The facts that neonatal pneumonia is relatively common, potentially life-threatening and difficult to diagnose makes it a challenging condition for the neonatologist.