Epidemiological findings are reported from pig breeding units that were visited repeatedly and\ud sampled intensively for environmental Salmonella contamination. Eight pig breeding units\ud previously associated with Salmonella Typhimurium were visited during up to seven years. Samples\ud from voided faeces, surfaces, fomites and wildlife were cultured. Certain serovars were isolated\ud repeatedly on certain units, whilst others were detected only once or intermittently. A few serovars\ud were isolated consistently on some units but only intermittently on others. There was an association\ud between Salmonella in pens and in their immediate environment. S. Typhimurium was significantly\ud associated with growing pigs. Pens holding breeding stock for production herds were frequently\ud Salmonella-positive. Herds under common ownership showed similar serovar combinations.\ud Cleaning and disinfection was frequently ineffective. Wildlife serovars were typical of the associated\ud premises. On one unit, a low level of Salmonella was attributed to a small herd size, good cleaning\ud and disinfection and good rodent control. The study has shown that breeding herds are susceptible to\ud endemic infections with multiple Salmonella serovars and that cleaning, disinfection and vector\ud control may in many cases be inadequate. Finally, the prevalence of S. Typhimurium may be greater\ud in youngstock, which has important implications for public health

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