Abstract
BackgroundHouseholds are one of the major settings of influenza transmission in the community and transmission is frequently initiated by school-aged children. We surveyed households with primary school (PS) and/ or junior high school (JH) children for the 2012–13 influenza season in Odate, Japan then characterized the epidemiology of influenza household transmission as well as estimated the serial intervals.MethodsWe delivered a self-reported questionnaire survey to households with PS and/or JH school children in Odate City, Japan. Influenza A (H3N2) virus predominantly circulated during the 2012–13 influenza season. We investigated the epidemiological characteristics of within-household transmission and calculated the serial intervals (SI). SIs were drew by a non-parametric model and compared with parametric models by the Akaike Information Criterion. The covariable contributions were investigated by the accelerated failure model.ResultsHousehold influenza transmission was identified in 255 out of 363 household respondents. Primary school (PS) children accounted for 45.1 % of primary cases, and disease transmission was most commonly observed between PS children and parents, followed by transmission from PS children to siblings. In primary cases of PS or JH children, younger age and longer absence from school were significantly associated with household transmission events. The mean SI was estimated as 2.8 days (95 % confidence interval 2.6-3.0 days) in the lognormal model. The estimated acceleration factors revealed that while secondary school age and the absence duration > 7 days were associated with shorter and longer SIs, respectively, antiviral prescriptions for primary cases made no contribution.ConclusionsHigh frequencies of household transmission from primary school with shorter SI were found. These findings contribute to the development of future mitigation strategies against influenza transmission in Japan.Electronic supplementary materialThe online version of this article (doi:10.1186/s12879-015-1007-8) contains supplementary material, which is available to authorized users.
Highlights
Households are one of the major settings of influenza transmission in the community and transmission is frequently initiated by school-aged children
Junior high (JH) and primary school (PS) students accounted for the majority of cases (71.1 %), but a substantial number of cases developed in mothers, pre-school children and fathers (9.2 %, 6.5 % and 6.1 % respectively)
Grandparents and other adults accounted for 7.3 % of primary cases and 42.2 % of secondary cases (p < 0.0001)
Summary
Households are one of the major settings of influenza transmission in the community and transmission is frequently initiated by school-aged children. Household studies usually measure the secondary infection risk; typically the secondary attack rate (SAR) This proportional parameter enables us to estimate the number of subsequent cases and evaluate the risk ratio, especially by age group. Another important parameter is the serial interval (SI), defined as the time between the onset of specific signs and the symptoms of a primary case and the onset of a secondary case [12, 13]. This parameter characterises the infectiousness profile and determines the rate of epidemic growth. We can elucidate (at least partially) the influenza transmission dynamics [14]
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