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Table 3 Incidence of influenza-associated influenza-like illness (ILI) in the municipal district of Suzhou, April 2011-March 2014 (95 % CI)

From: Influenza-associated outpatient visits among children less than 5 years of age in eastern China, 2011–2014

Parameters Apr 2011-Mar 2012 Apr 2012-Mar 2013 Apr 2013-Mar 2014
Proportion of ILI in outpatient visits (%) 26.1 24.8 23.2
Proportion of influenza in ILI (%) 23.3 13.3 9.5
Total No. of outpatient visits at SCHa 301,278 319,086 343,927
Estimated total no. of outpatient visits for ILI at SCHb 72,244 (61,292–83,196) 81,782 (71,199–92,365) 85,676 (79,117–92,235)
Estimated total no. of influenza-associated ILI at SCHc 8,956 (5,657–13,018) 7,172 (2,557–12,872) 10,965 (5,579–17,132)
Resident population of children <5 years in the catchment area of SCHd 99,622 111,663 123,207
Proportion of ILI who sought care at SCH (%)e 51.6 44.0 41.5
Incidence of influenza-associated ILI per 100 person-year 17.4 (11.0–25.3) 14.6 (5.2–26.2) 21.4 (10.9–33.5)
  1. aTotal number of outpatient visits at SCH from catchment area was estimated by applying the proportion of ILI cases from catchment area to the total number of outpatient visits at SCH; bEstimated by multiplying the month-specific number of outpatient visits at SCH by the month-specific proportion of ILI in outpatient visits; month specific data used as influenza has a seasonal epidemic pattern; cEstimated by multiplying the month-specific estimated number of outpatient visits for ILI at SCH by the month-specific proportion testing positive for influenza virus; month specific data used as influenza has a seasonal epidemic pattern; dResident population in the catchment area (refers to people living in Suzhou for more than 6 months) was obtained from Suzhou immunization program database;e We used data from 1st HUS (Jan 2012) in the estimation period of Apr 2011-Mar 2012, data from 2nd HUS (Oct 2012) and 3rd HUS (Jan 2013) in the estimation period of Apr 2012-Mar 2013, and data from 4th HUS (Apr 2013), 5th HUS (Aug 2013) 6th (Nov 2013) and HUS 7th (Jan 2014) in the estimation period of Apr 2013-Mar 2014