Burden of Influenza in Less Than 5-Year-Old Children Admitted to Hospital with Pneumonia in Developing and Emerging Countries: A Descriptive, Multicenter Study

Influenza is a major cause of mortality and morbidity in young children worldwide. According to a meta-analysis published in 2011,1 a total of one million severe, acute, lower respiratory infections and between 28,000 and 111,500 deaths may be attributable annually to influenza-associated infections in children younger than 5 years, with 99% of these deaths occurring in developing countries. Influenza viruses are recognized as risk factors for secondary bacterial infections or co-colonizations2 or as etiological agents of viral pneumonia.3 Therefore, detection of influenza viruses in upper respiratory samples from children with pneumonia might be related to one of these phenomena or both. The burden of influenza has been determined in industrialized countries, with attack rates reaching between 10% and 20% during seasonal outbreaks or higher during pandemics,4 but data from developing and emerging nations remain scarce.5 We conducted a descriptive study of less than 5-year-old children hospitalized because of pneumonia in developing and emerging countries. The main objective was to estimate the age- and country-stratified proportion of influenza-related pneumonia in this population. Secondary objectives were the description of clinical and microbiological characteristics of—particularly bacterial coinfections in—influenza-related pneumonia cases.