| Influenza is an acute respiratory illness caused by influenza virus, which is one of the leading cause of morbidity and mortality in children. Influenza epidemic has obvious seasonal and regional characteristics. Each year influenza epidemics cause substantial outpatient visits and hospitalizations in children. However, influenza-associated hospitalizations account for only a small proportion of all influenza infections in children. The majority component of influenza disease burden is outpatient cases. The outpatient visit rate in children under 5 years can be 10-250 times higher than hospitalization rate, which causes substantial economic and societal burden. Except for the substantial medical cost, outpatient visit attributable to influenza can also cause non-medical cost such as transportation as well as indirect cost. China is a country with high incidence of influenza. However, due to lack of data on disease burden of influenza in children, influenza vaccination has not been listed in the national immunization program. The influenza vaccination rate in chidren is still low. Therefore, it is necessary to develop research on epidemiology and disease burden of influenza in children, in order to provide evidenc for influenza prevention and control strategy. Taking Suzhou as our study site, we conducted surveillance for influenza-like illness (ILI) and virological testing in the outpatient setting at Suzhou University Affiliated Children’s Hospital, in order to understand the epidemiological and clinical characteristics of children with influenza, to estimate the direct and indirect economic burden, and to estimate the outpatient visit rate of influenza-associated ILI combining the healthcare utilization surveys in children in the community, to comprehensively evaluate the disease burden of influenza among children in the outpatient setting in Suzhou.1. From April 2011 to March 2014, we conducted outpatient ILI surveillance, patient enrollment and swab specimen collection in children under 5 years consulted at Suzhou Children’s Hospital. We used molecular biological method to detect influenza virus and other respiratory viruses, and questionnaire survey to understand the clinical characteristics, past history and medical seeking process of study subjects. During the study period, we totally identified 11,817 outpatient ILI cases, the proportion of ILI was 24.1%. We enrolled 3834 ILI cases, with respiratory viral detection rate of 37.6% and influenza virus detection rate of 16.9%. The epidemics of influenza had obvious seasonal characteristic:the winter-spring peak occurred in 2012 and 2014, but was at low to moderate epidemic level in 2013; the summer peak only occurred in 2012. The proportion of ILI and influenza percent positive decreased year by year during the three years, with influenza A and influenza B alternately predominating. The winter peak of respiratory syncytial virus (RSV) partly overlapped with that of influenza virus. The majority of influenza positive cases were children older than 2 years, and the proportion of influenza positive cases increased with age. We recommended to promote influenza vaccination among children with this age group. Cough and rhinorrhea were the most common symptoms of influenza cases. Symptoms of cough and convulsion appeared more frequently in influenza positive cases, which could help guide clinicians to distinguish influenza cases. Influenza complications occurred in 42.2% of outpatient influenza cases, including bronchitis, pneumonia, bronchial asthma, croup, sinusitis and febrile seizures. Children with underlying medical condition, history of immunosuppressor use and premature birth were more likely to develop influenza complications, the adjusted odds ratio (OR) were 2.74,1.78 and 3.22, respectively. We recommended to strengthen the educational efforts of influenza control and prevention and promote influenza vaccination in these children, in order to reduce the morbidity of influenza as well as development of influenza complications.2. For many times we used population-based stratified random sampling method to do the telephone questionnaire survey in the child’s parents or guardians to understand the occurrence of ILI in the past one month and their medical seeking behaviors. The surveys were conducted once each half year or each quarter, for totally 7 times and about 1800 subjects each time. In the surveyed 21,599 children, 6.6% reported to have symptoms of ILI during the past one month. The occurrence of reported ILI in the community was greatly affected by influenza season. The occurrence of ILI tended to increase by age, and was higher in children from municipal district than those from county-level cities. In the reported ILI cases,82.3% had visited hospital. The healthcare utilization rate was high in children with ILI. There were a variety of hospitals to choose. Distance is the major factor influencing the choice of hospitals in ILI child’s parents. Among the ILI children who sought care,27.8% chose to visit Suzhou Children’s Hospital. The proportions of ILI who sough care at Suzhou Children’s Hospital were 45.6%,42.4% and 5.3% in Gusu district, new urban district and county-level cities, respectively, significantly higher in municipal district than in county-level cities. Among children who didn’t seek care, the majority (84.9%) of their parents chose self medication because they didn’t think the illness was severe enough. Although the occurrence of ILI in children in the community sigfinicantly varied by influenza season, the healthcare seeking behaviors of ILI cases were relatively stable, which could provide evidence for disease burden estimation based on hospital surveillance. Besides, the impact of distance on healthcare utilization should be considered and further adjusted.3. In order to estimate the outpatient visit rate of influenza-associated ILI in children in Suzhou district based on ILI surveillance at Suzhou Children’s Hospital, we firstly reviewed the regional distribution of outpatient ILI cases and hospitalized cases in Suzhou Children’s Hospital for the past several years, then we defined the municipal district and two county-level cities (Kunshan and Wujiang) as the catchment area of Suzhou Children’s Hospital. We used the ILI surveillance data and influenza virus testing results to estimate the total number of ILI cases with influenza tested positive at Suzhou Children’s Hospital; we used the proportion of community ILI children who sought care at Suzhou Children’s Hospital from healthcare utilization surveys to adjust the resident population<5 years to estimate the denominator population in the catchment area of Suzhou Children’s Hospital. By dividing the former one by the latter one, we could calculate the outpatient visit rate of influenza-aassociated ILI in children in the catchment area. The estimated outpatient visit rates of influenza-associate ILI for the three years were 21.5,15.4 and 21.3 per 100 person-years respectively. For the municipal district alone, the estimated outpatient visiti rates were 20.6,14.7 and 20.4 per 100 person-years respectively. The age-specific outpatient visit rates of influenza-associated ILI were 5.4,20.9 and 21.0 in children aged 0-5m,6-23m and 24-59m respectively. This estimation method could provide reference for other regions to estimate the influenza-associated disease burden.4. Taking 3834 ILI cases enrolled from outpatient ILI surveillance at Suzhou Children’s Hopsital from April 2011 to March 2014 as study subjects, we conducted telephone follow-up survey to understand the medical seeking process and related costs including transportation cost and nourishment cost, to understand the school absence in children, work absence in their parents and the salary losses. Through the outpatient Hospital Information System (HIS) in Suzhou Children’s Hospital, we inquired the direct medical costs of the subjects. Among influenza cases,49.5% had over-the-counter medication,31.0% had visited other hospital. Children with health insurance and with history of immunosuppressor use had more outpatient visits. The average direct medical cost for outpatient influenza cases was 317.4 RMB, which was higher than other respiratory virus infected cases and virus negative cases. For the components of outpatient cost, medicine fee accounted for the highest proportion (73.1%), followed by laboratory test fee (11.3%). The influenza children with complications had more outpatient visits, and their outpatient costs were twice as those without complications. Age is a factor influencing the outpatient cost of influenza children. The older the child was, the higher the outpatient cost was. We recommended to promote influenza vaccination in children older than 2 years, especially in those with low immunity and at high risk of influenza complications, to significantly reduce the medical expenses, which might have high economic benefit. The average direct non-medical cost incurred during medical seeking was 100.0 RMB, which consisted primarily of transportation cost.57.9% of parents had work absence due to taking care of their child, and missed a mean of 1.8 work days, which resulted in an average salary losses (indirect cost) of 142.0 RMB, accounted for 1/4 of total costs. Besides, influenza also imposed great socio-economic impact on children and their family. Among influenza positive children who were attending daycare,36.5% of them had daycare absence, and missed a mean of 1.9 days.42.5% of family members developed similar respiratory symptoms after onset of the child’s illness, and 90.5% of them had visited hospital or taken medicines. Both of the two proportions were higher than influenza negative children, which indicated high risk of intrafamilial transmission in influenza positive children. If the sick family members sought care or missed work, it might aggravate the family’s economic burden.5. Conducted questionnaire survey among the ILI cases enrolled from outpatient ILI surveillance at Suzhou Children’s Hospital to collect the average cost per outpatient influenza case, including direct medical cost and direct non-medical cost, as well as the missed parental workdays and lost salary due to care for the sick child. Upon this, we took the incidence-based bottom-up method and combined the estimated outpatient visit rate of influenza-associated ILI in Suzhou district, to calculate the direct economic burden caused by influenza-associated outpatient visit in children in Suzhou district. We used the human capital method to calculate the indirect economic burden. From the perspective of family, the economic burden per capita was 65.3 RMB, the direct and indirect burden ratio was 1.6:1. From the perspective of society, the economic burden per capita was 99.6 RMB, the direct and indirect burden ratio was 0.9:1. The economic burden of outpatient influenza children increased with age. The economic burden of children aged 6-23m and 24-59m was significantly higher than in children aged 0-5m. The proportion of indirect burden decreased with age. The estimated economic burden was higher than the cost of influenza vaccination, which indicated that influenza vaccination in children (especially in children above 6m) might have great economic benefit. However, the estimation of disease burden of influenza was greatly influenced by influenza season, so it was necessary to conduct prospective study for consecutive years. |
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