Surveillance data for clinical disease in cattle in Great Britain due to Salmonella infections were analysed for the period 2003 to 2008 in order to describe seasonality and to investigate possible associations between Salmonella diagnoses and other variables such as region, climate, age and production type. A clear seasonal pattern was shown for Salmonella infection, coinciding with the second half of the year. The incidence of Salmonella Dublin and Salmonella Typhimurium was highest in the west of the country, which has the greatest cattle density, but this was not a feature of diagnoses with other serovars. Abortion was a more common clinical sign of S Dublin infections, but was relatively unusual in the case of S Typhimurium. The observed clinical picture and age of affected animals were largely determined by the seasonality of dairy cattle calving in Great Britain.

The analysis of laboratory data can provide information about the health of livestock populations; in Great Britain the Veterinary Investigation Diagnosis Analysis (VIDA) system has provided such data since 1975. However VIDA covers only known diagnoses, with limited epidemiological characterisation. The unexpected outbreak of bse showed that it was necessary to improve surveillance to detect new diseases, and a necessary update of the VIDA database for the millennium date change provided the opportunity. The information required to enhance the value of laboratory data was identified, a new form and database, 'FarmFile', were designed to record it, and they began to be used in 1999. The detection of new diseases depends on making comparisons with the expected or 'usual' levels of unexplained disease. The data are analysed quarterly to assess any changes in the levels of unexplained disease in different species, categorised in terms of clinical sign or body system, by comparison with previous years. No new diseases have been detected either through FarmFile or more traditional means since the new analyses started in earnest in 2004, but they have indicated that an unexplained event was not a new disease of concern, and developments continue to improve the system's sensitivity and specificity.

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