Emerging Themes in Epidemiology

Surprisingly little is known regarding the human mixing patterns relevant to the spread of closecontact infections, such as measles, influenza and meningococcal disease. This study aims to estimate the number of partnerships that individuals make, their stability and the degree to which mixing is assortative with respect to age. We defined four levels of putative at-risk events from casual (physical contact without conversation) to intimate (contact of a sexual nature), and asked university student volunteers to record details on those they contacted at these levels on three separate days. We found that intimate contacts are stable over short time periods whereas there was no evidence of repeat casual contacts with the same individuals. The contacts were increasingly assortative as intimacy increased. Such information will aid the development and parameterisation of models of close contact diseases, and may have direct use in outbreak investigations. Background Mathematical models have long been used to further our understanding of the spread of close-contact infections, such as measles and tuberculosis, and make quantitative predictions regarding the possible impact of control policies [1-4]. Largely through the development and exploration of these models the pivotal role of the patterns of host mixing to the spread of such pathogens has been acknowledged [2,4-7]. Broadly, the models employed by epidemiologists can be subdivided into two [8], according to their assumptions regarding the stability of contacts: those that employ the mass-action assumption, or variants of this [1-6], in which contacts are instantaneous and independent i.e. once contacted, individuals are no more (or less) likely to contact each other in the future; or network models and their variants in which individuals are thought of as the nodes in a network and the links between them their contacts [9-11]. These models tend to assume that individuals form relatively stable partnerships (some, indeed, assume a static network). Micro-simulation, or agent-based models (e.g. [10]) in which individuals are often assumed to reside in households travel to schools or workplaces daily and so on, fall into the latter category of models in which individuals are (often implicitly) assumed to form relatively stable contact networks. Which of these classes of model best fits reality: one in which at least some of the contacts are stable (such as network models), or one in which contacts are transient and constantly changing (as in mass action variants)? Does this alter for different close-contact infections? Furthermore, are the characteristics of those that are contacted random or is there a degree of preferred, or assortative mixing? Published: 14 August 2006 Emerging Themes in Epidemiology 2006, 3:10 doi:10.1186/1742-7622-3-10 Received: 26 April 2006 Accepted: 14 August 2006 This article is available from: http://www.ete-online.com/content/3/1/10 © 2006 Edmunds et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Emerging Themes in Epidemiology 2006, 3:10 http://www.ete-online.com/content/3/1/10