Trends and Changes in Influenza-associated Hospitalizations in Children During 25 Years in Finland, 1993-2018

Background:Limited long-term data are available on potential changes in the demographics and management of children hospitalized with influenza. Methods:We identified all children <= 15 years old hospitalized with virologically confirmed influenza at Turku University Hospital, Finland, during the 25-year period of July 1993-June 2018. Data on clinical variables, comorbidities and management were retrieved directly from the medical records. Population-based rates of hospitalization were calculated using official annual databases of children living in the hospital catchment area. Results:Between 1993-1998 and 2013-2018, the median age of children increased from 1.3 years to 3.3 years (P < 0.0001). The proportion of children <2 years of age decreased from 65.2% to 36.8%, whereas the proportion of children 6-15-year-old increased from 13.0% to 36.2% (P < 0.0001 for both). The population-based rates of hospitalization decreased by 49% in children 1 year of age (incidence rate ratio, 0.51; 95% confidence interval: 0.27-0.92; P = 0.018) and increased by 194% in children 6-15 years old (incidence rate ratio, 2.94; 95% confidence interval: 1.70-5.32; P < 0.0001). The median duration of hospitalization shortened from 2.0 days (interquartile range [IQR], 1.0-4.0) to 1.0 day (IQR, 1.0-2.0; P < 0.0001). Conclusions:During the 25 years, the median age of hospitalized children increased by 2 years, while the duration of hospitalization shortened.