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 (SCH) to estimate influenza-associated hospitalizations in SCH 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 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 aged 0-5 months; 8 (95% CI: 7-10) per 1,000 children aged 6-23 months; and 5 (95% CI: 4-5) per 1,000 children aged 24-59 months respectively.

CONCLUSIONS:

From 2011-2016, influenza-associated SARI hospitalization rates in children aged younger than 5 years of age in Suzhou, China were high, particularly among children aged 0-5 months. 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.