Child hospital admissions associated with influenza virus infection in 6 Spanish cities (2014-2016) Hospitalizaciones infantiles asociadas a infección por virus de la gripe en 6 ciudades de España (2014-2016)

Introduction: There are only a limited number of studies on the impact of influenza in the Spanish child population. The present work intends to increase this knowledge by studying some key aspects, such as the incidence of hospital admissions, clinic variables, comorbidities, and the vaccination status in the hospitalised children. Methods: A retrospective, observational study was conducted by reviewing the medical records of children under 15 years and hospitalised due to community acquired influenza confirmed microbiologically, during 2 ́flu seasons (2014-2015 and 2015-2016). The study was carried out in 10 hospitals of 6 cities, which represent approximately 12% of the Spanish child population. Results: A total of 907 children were admitted to hospital with main diagnosis of influenza infection (447 < 2 years), estimating an average annual rate of hospitalisation incidence of 0.51 cases / 1,000 children (95% CI; 0.48-0.55). Just under half (45%) of the cases had an underlying disease considered a risk factor for severe influenza, and most (74%) had not been vaccinated. The percentage of children with underlying diseases increased with age, from 26% in children < 6 months to 74% in children >10 years. Admission to the PICU was required in 10% (92) of the cases, mainly due to acute respiratory failure. Conclusion: Influenza continues to be an important cause of hospitalisation in the Spanish child population. Children < 6 months of age and children with underlying diseases make up the majority (> 50%) of the cases. Many of the severe forms of childhood influenza that occur today could be avoided if current vaccination guidelines were met.