Determining the dynamics of influenza transmission by age

Abstract

Background: It is widely accepted that influenza transmission dynamics vary by age; however methods to quantify the reproductive number by age group are limited. We introduce a simple method to estimate the reproductive number by modifying the method originally proposed by Wallinga and Teunis and using existing information on contact patterns between age groups. We additionally perform a sensitivity analysis to determine the potential impact of differential healthcare seeking patterns by age. We illustrate this method using data from the 2009 H1N1 Influenza pandemic in Gauteng Province, South Africa.

Results: Our results are consistent with others in showing decreased transmission with age. We show that results can change markedly when we make the account for differential healthcare seeking behaviors by age.

Conclusions: We show substantial heterogeneity in transmission by age group during the Influenza A H1N1 pandemic in South Africa. This information can greatly assist in targeting interventions and implementing social distancing measures.

Figure 1

Epidemic curves by age group.

Figure 2

Smoothed estimates of R _t for the transmission matrix based on (a) all contacts involving physical contact and (b) all close contacts using the South African contact matrices.

Figure 3

Estimated R0 by age group for each of the contact trace matrices from the nine countries in the PolyMod study using (a) all contacts, and (b) physical contacts.

Figure 4

Estimates of R₀ by age groups using contact matrices from South Africa and separately each of the eight countries in the Mossong et al. study. (a) results for all close contacts and (b) for contacts involving physical touch.