Direct and indirect contacts between cattle farms in north-west England.

Little is known regarding the types and frequencies of contact that exist between farms and which of these may act as pathogen transmission routes; however it is likely that farms demonstrate considerable heterogeneity in such contacts. In this cross-sectional study, we explored the direct and indirect contact types and frequencies that exist between cattle farms within a region, focusing on potential routes of pathogen transmission. The owners/managers of 56 farms located in a 10 km by 10 km study area in north-west England were administered an interview-based questionnaire between June and September 2005. Information was obtained relating to contact types and frequencies, including those involving animal movements, equipment sharing between farms and any contractors or companies visiting the farms. The data was explored using hierarchical cluster analysis and network analysis. There was considerable variation between farms arising from different contact types. Some networks exhibited great connectivity, incorporating approximately 90% of the farms interviewed in a single component, whilst other networks were more fragmented, with multiple small components (sets of connected farms not linked with other farms). A range of factors influencing contact between farms were identified. For example, contiguous farms were more likely to be linked via other contacts, such as sharing of equipment and direct farm-to-farm animal movements (p<0.001 and p=0.02, respectively). The frequency of contacts was also investigated; it is likely that the amount of contact a farm receives from a company or contractor and whether or not biosecurity is performed after contact would impact on disease transmission potential. We found considerable heterogeneity in contact frequency and that many company and contractor personnel undertook little biosecurity. These findings lead to greater understanding of inter-farm contact and may aid development of appropriate biosecurity practices and control procedures, and inform mathematical modelling of infectious diseases.