Aims: To determine a temperature-humidity-time treatment that eliminates Salmonella and Escherichia coli in substrates representing organic matter in poorly cleaned poultry houses, i.e. worst case scenario laboratory tests. Methods and Results: Organic matter (poultry faeces and feed) in a 2AE5-cm layer was inoculated with 2 · 10 5 -3 · 10 6 Salmonella g )1 , left undried or dried at ca. 30% relative humidity (RH) during a 10-day period, and temperature increased at 1°C h )1 to the final heating temperature of 50, 55, 60, 65 or 70°C and held at 16-30 or 100% RH. All samples were tested for Salmonella according to predetermined sampling time schedules and faecal samples were also tested for naturally occurring E. coli. Overall, humidity was an important factor in the elimination of Salmonella and E. coli. Results for recovery of Salmonella and E. coli were highly associated. Conclusions: The application of ‡60°C and 100% RH during a 24-h period eliminated Salmonella and E. coli in all samples. Escherichia coli could be used as an indicator bacterium for the elimination of Salmonella. Significance and Impact of the Study: The results from worst case scenario laboratory tests could be applied in steam heating of persistently Salmonella-infected poultry houses. The use of E. coli as an indicator bacterium for the validation of Salmonella results should be considered.

Aims: To monitor if a temperature-humidity-time treatment found to be effective in eliminating Salmonella in laboratory trials (Gradel et al. 2003) was efficient against Salmonella in naturally infected layer houses. Methods and Results: Six layer houses with natural Salmonella infections were steam treated in a download period, aiming at ‡60°C and 100% relative humidity (RH) during a 24-h period, with or without the addition of 30 ppm formaldehyde. In addition, two control layer houses were disinfected chemically. Salmonella samples taken from predetermined sites before and after treatment were tested qualitatively for Salmonella and coliforms. Samples with indicator bacteria (feed inoculated with Escherichia coli or Enterococcus faecalis and faeces with naturally occurring E. coli and enterococci) were placed during steam-treatment at 12 sites in each house (where the temperature was logged at 5-min intervals) and tested for surviving bacteria. Generally, the field test results confirmed the results of laboratory tests, especially when 30 ppm formaldehyde was added to the steam. In well-sealed houses, the recommended temperature-humidity-time scheme was accomplished at a minimum of 10 cm above floor level within 1 h. Conclusions: A steam treatment of ‡60°C and 100% RH during a 24-h period with the addition of 30 ppm formaldehyde at the beginning of the process is recommended for eliminating Salmonella from naturally infected poultry layer houses. Significance and Impact of the Study: A specific recommendation for the elimination of Salmonella in poultry houses can be given.

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