Fine-scale family structure shapes influenza transmission risk in households: Insights from primary schools in Matsumoto city, 2014/15

Abstract

Households are important settings for the transmission of seasonal influenza. Previous studies found that the per-person risk of within-household transmission decreases with household size. However, more detailed heterogeneities driven by household composition and contact patterns have not been studied. We employed a mathematical model that accounts for infections both from outside and within the household. The model was applied to citywide primary school seasonal influenza surveillance and household surveys from 10,486 students during the 2014/15 season in Matsumoto city, Japan. We compared a range of models to estimate the structure of household transmission and found that familial relationship and household composition strongly influenced the transmission patterns of seasonal influenza in households. Children had a substantially high risk of infection from outside the household (up to 20%) compared with adults (1-3%). Intense transmission was observed within-generation (between children/parents/grandparents) and also between mother and child, with transmission risks typically ranging from 5-20% depending on the transmission route and household composition. Children were identified as the largest source of secondary transmission, with family structure influencing infection risk.

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“…However, the precise combination of setting and type of contact that will be important for transmission will depend on the infection being considered. There is evidence that both physical contacts [18, 6] and conversational contacts [8] may be relevant for capturing the transmission dynamics of acute respiratory infections such as Streptococcus pneumoniae and influenza A/H1N1p, and for influenza, there can be substantial transmission in households [10] and schools [21, 5]. How to weight the respective contributions of conversational and physical contacts to overall population transmission will depend on the pathogen.…”

Dynamics of COVID-19 under social distancing measures are driven by transmission network structure

“…Many more studies have examined the role of household transmission in influenza spread, but the results are also equivocal: a review by Tsang et al found that household secondary attack rates varied from 1–40% across studies [ 45 ]. A massive cohort study from Japan recently shone some light on this complexity; finding that the risk of household influenza transmission was highly dependent on household structure and on the familial relationship between the primary and secondary case [ 46 ].…”

Dynamics of COVID-19 under social distancing measures are driven by transmission network structure

“…Many more studies have examined the role of household transmission in influenza spread, but the results are also equivocal: a review by Tsang et al found that household secondary attack rates varied from 1-40% across studies [31]. A massive cohort study from Japan recently shone some light on this complexity; finding that the risk of household influenza transmission was highly dependent on household structure and on the familial relationship between the primary and secondary case [32]. They also found that the relative role of external vs household spread was highly age-dependent, children were much more likely to be infected outside the home (~80% of risk), while for adults infection within the home dominated (50% or more).…”