Population-Based Pediatric Hospitalization Burden of Lineage-Specific Influenza B in Hong Kong, 2004-2014.

Background: Influenza B virus has been perceived to cause less disease burden and milder disease compared with influenza A, but recent studies suggest that influenza B does have a significant impact. We aimed to estimate the burden of influenza B virus infections on hospitalizations in Hong Kong, in the context of virus lineage changes over time.

Methods: The pediatric age-specific rates of influenza B hospitalization in Hong Kong for 2004-2014 were estimated based on admissions to 2 hospitals that together catered for 72.5% of all pediatric admissions on Hong Kong Island. Influenza B virus was detected by immunofluorescence and culture on nasopharyngeal aspirates. Lineage typing was performed by real-time reverse-transcription polymerase chain reaction.

Results: A total of 5085 children were recruited on 1 designated day each week, year-round during the 11 years, and 221 (4.3%) tested positive for influenza B. Hospitalization rates were highest in children aged 2 to <5 years with year-to-year variation. Victoria-lineage viruses appeared to be associated with a greater fraction of influenza B hospitalizations in children than of influenza B infections in the general community. Influenza B did not cause significant hospitalization in infants <1 year of age.

Conclusions: We report one of the first population-based, age- and lineage-specific studies of pediatric hospitalization for influenza B. We found that changes in lineage were associated with higher hospitalization rates and documented that Victoria lineage viruses were associated with greater pediatric hospitalization burden compared with Yamagata lineage viruses.