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

BMC Infectious Diseases

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

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 SCH^a	301,278	319,086	343,927
Estimated total no. of outpatient visits for ILI at SCH^b	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 SCH^c	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 SCH^d	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)

^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 1^st HUS (Jan 2012) in the estimation period of Apr 2011-Mar 2012, data from 2^nd HUS (Oct 2012) and 3^rd HUS (Jan 2013) in the estimation period of Apr 2012-Mar 2013, and data from 4^th HUS (Apr 2013), 5^th HUS (Aug 2013) 6^th (Nov 2013) and HUS 7^th (Jan 2014) in the estimation period of Apr 2013-Mar 2014

ISSN: 1471-2334