Household Transmission of Influenza Virus

Abstract

Human influenza viruses cause regular epidemics and occasional pandemics with a substantial public health burden. Household transmission studies have provided valuable information on the dynamics of influenza transmission. We reviewed published studies and found that once one household member is infected with influenza, the risk of infection in a household contact can be up to 38%, and the delay between onset in index and secondary cases is around 3 days. Younger age was associated with higher susceptibility. In the future, household transmission studies will provide information on transmission dynamics including the correlation of virus shedding and symptoms with transmission, and the correlation of new measures of immunity with protection against infection.

Fine-scale family structure shapes influenza transmission risk in households: insights from a study of primary school students in Matsumoto city, 2014/15

“…With a detailed dataset consisting of up to 10,000 households, the present study was able to employ a highly flexible modelling framework to explore previously used modelling assumptions in great detail. A decrease of the per-person risk of within-household infections with household size has been observed in previous studies (8); our model selection supported that this reduced effect of household contact is better characterised as a function of the total amount of contact experienced by an individual ( C k ) rather than the household size ( N ), and that the relationship follows an inverse square root law. Previous modelling studies used different frameworks to study the relationship between SITP and household composition.…”

“…Conversely, children may exhibit lower susceptibility if the vaccine uptake for them is higher than adults. The majority of household transmission studies from a systematic review (8) reported significant association between susceptibility and age (although this becomes the minority when limited to the studies with PCR-confirmed cases). Our baseline model assumes that transmissibility β is identical between individuals, but in reality transmissibility might depend on the age of the susceptibles.…”

“…Households are considered as one of the main layers of transmission, as individuals come in close contact with each other both conversationally and physically on a daily basis (5–7). Many epidemiological studies have used household data to investigate the transmission dynamics of influenza within households (8,9), particularly in terms of the secondary attack rate (the number of household secondary cases divided by the number of household members at risk). However, this assumes that an index case (the first case in a household, who is considered to be infected outside the household) is responsible for all subsequent household cases, and that all the other household members are equally at the risk of secondary infection.…”

“…The possibility of co-primary infections and tertiary transmissions are neglected under such assumptions (8); potentially heterogeneous transmission patterns between household members are also radically simplified. The former limitation can be addressed by mathematical models which separately estimate the risk of infection from outside the household (community probability of infection; CPI) and the within-household transmission risk (10).…”

How Modelling Can Enhance the Analysis of Imperfect Epidemic Data

“…These methods were used extensively to characterize the transmission of influenza in households from a powerful study design where household contacts of confirmed influenza cases are followed-up for a few weeks after symptom onset of the first case. These analyses provided key insights about the determinants of influenza transmissionsuch as estimates of the risk of household transmission, and how this varies with household size, the infectivity and susceptibility of children relative to adults, the serial interval of influenza (which is important to determine for how long cases should be isolated, to assess the impact of treatment delays on transmission or estimate other parameters such as the reproduction number), the relationship between viral shedding and infectivity, and the protective effect of baseline antibody titres [2,[22][23][24][25][26][27][28]. These methods have also been used to investigate transmission in more complex social settings such as a school [29] or a small village [30].…”