Small-world topology of UK racing: the potential for rapid spread of infectious agents

Reasons for performing study: The topology of the network of contacts between individuals has important effects on infectious disease dynamics within a population. Here we examine for the first time a network of contacts between training yards that occurred through racing. Objectives: To explore the topology of this network and to consider the effects of the network on the potential for disease transmission. Methods: Race data from one week was analysed. Contacts were defined as occurring between trainers that raced horses in the same race and hence one trainer could contact another trainer several times. A connection was said to exist between trainers who contacted each other at least once. The network of contacts and connections that occurred during the study period was reconstructed and analysed. Results: All 466 trainers formed a single large network. The network of contacts had a short average path length and high clustering and was, therefore, characteristic of a 'small world network'. The probability distribution of the number of contacts was scale-free, whereas that for the number of connections followed a single-scale. The effect of the network would be to increase R-0, such that an agent that would tend toward extinction in a homogenously mixing population may persist in the observed network. Conclusions: The observed small world network topology has important implication for the transmission and, therefore, the control of infectious agents in this population. Potential relevance: Effective disease control and surveillance must take account of the contact structure of the population. Further studies investigating other contact definitions and other populations are now required.