Influenza-associated Hospitalization in Children Younger Than 5 Years of Age in Suzhou, China, 2011–2016

Abstract

Background: Studying the burden and risk factors associated with severe illness from influenza infection in young children in eastern China will contribute to future cost-effectiveness analyses of local influenza vaccine programs. Methods: We conducted prospective, severe acute respiratory infection (SARI) surveillance at Suzhou University–Affiliated Children’s Hospital to estimate influenza-associated hospitalizations in Suzhou University–Affiliated Children’s Hospital by month in children younger than 5 years of age from October 2011 to September 2016. SARI was defined as fever (measured axillary temperature ≥ 38°C) and cough or sore throat or inflamed/red pharynx in the 7 days preceding hospitalization. We combined SARI surveillance data with healthcare utilization survey data to estimate and characterize the burden of influenza-associated SARI hospitalizations in Suzhou within this age group in the 5-year period. Results: Of the 36,313 SARI cases identified, 2,297 from respiratory wards were systematically sampled; of these, 259 (11%) were influenza positive. Estimated annual influenza-associated SARI hospitalization rates per 1,000 children younger than 5 years of age ranged from 4 (95% confidence interval [CI], 2–5) in the 2012–2013 season to 16 (95% CI, 14–19) in the 2011–2012 season. The predominant viruses were A/H3N2 (59%) in 2011–12, both A/H1N1pdm09 (42%) and B (46%) in 2012–13, A/H3N2 (71%) in 2013–14, A/H3N2 (55%) in 2014–15 and both A/H1N1pdm09 (50%) and B (50%) in 2015–16. The age-specific influenza-associated SARI hospitalization rates for the 5-year period were 11 (95% CI, 8–15) per 1,000 children 0–5 months of age; 8 (95% CI, 7–10) per 1,000 children 6–23 months of age and 5 (95% CI, 4–5) per 1,000 children 24–59 months of age, respectively. Conclusions: From 2011 to 2016, influenza-associated SARI hospitalization rates in children aged younger than 5 years of age in Suzhou, China, were high, particularly among children 0–5 months of age. Higher hospitalization rates were observed in years where the predominant circulating virus was influenza A/H3N2. Immunization for children > 6 months, and maternal and caregiver immunization for those < 6 months, could reduce influenza-associated hospitalizations in young children in Suzhou.