Title The Contribution of Social Behaviour to the Transmission ofInfluenza A in a Human Population

Variability in the risk of transmission for respiratory pathogens can result from several factors, including the intrinsic properties of the pathogen, the immune state of the host and the host’s behaviour. It has been proposed that self-reported social mixing patterns can explain the behavioural component of this variability, with simulated intervention studies based on these data used routinely to inform public health policy. However, in the absence of robust studies with biological endpoints for individuals, it is unclear how age and social behaviour contribute to infection risk. To examine how the structure and nature of social contacts influenced infection risk over the course of a single epidemic, we designed a flexible disease modelling framework: the population was divided into a series of increasingly detailed age and social contact classes, with the transmissibility of each age-contact class determined by the average contacts of that class. Fitting the models to serologically confirmed infection data from the 2009 Hong Kong influenza A/H1N1p pandemic, we found that an individual’s risk of infection was influenced strongly by the average reported social mixing behaviour of their age group, rather than by their personal reported contacts. We also identified the resolution of social mixing that shaped transmission: epidemic dynamics were driven by intense contacts between children, a post-childhood drop in risky contacts and a subsequent rise in contacts for individuals aged 35–50. Our results demonstrate that self-reported social contact surveys can account for age-associated heterogeneity in the transmission of a respiratory pathogen in humans, and show robustly how these individual-level behaviours manifest themselves through assortative age groups. Our results suggest it is possible to profile the social structure of different populations and to use these aggregated data to predict their inherent transmission potential. Citation: Kucharski AJ, Kwok KO, Wei VWI, Cowling BJ, Read JM, et al. (2014) The Contribution of Social Behaviour to the Transmission of Influenza A in a Human Population. PLoS Pathog 10(6): e1004206. doi:10.1371/journal.ppat. 1004206 Editor: Elodie Ghedin, New York University, United States of America Received January 16, 2014; Accepted May 7, 2014; Published June 26, 2014 Copyright: 2014 Kucharski et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was funded by the Wellcome Trust (University Award 093488/Z/10/Z), Fogarty International Centre (R01 TW008246-01), and Medical Research Council (Project Grant MR/J008761/1). The research leading to these results has received funding from the European Union Seventh Framework Programme (278433-PREDEMICS), US National Institutes of Health: MIDAS cooperative agreement (5U01GM076497), RAPIDD program from Fogarty International Centre with the Science & Technology Directorate, Department of Homeland Security, and Hong Kong Research fund for the Control of Infectious Disease. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: BJC has received research funding from MedImmune Inc., and consult for Crucell NV. DAC has acted as a consultant to Medimmune. These do not alter our adherence to all PLOS policies on sharing data and materials. * Email: s.riley@imperial.ac. uk