Effects of sample storage and delayed secondary enrichment on detection ofSalmonella spp in swine feces

Objective-To determine effects of fecal sample storage and delayed secondar y enrichment (DSE) on detection of Salmonella spp in swine feces. Sample Population-Fecal samples obtained from 84 pigs in a commercial herd, Procedure-Each fecal sample underwent 3 storage treatments: no storage,(ie, processed on the day of collection), storage at 4 C for 6 days, and storag e at -15 C for 14 days, After assigned storage treatments, all samples were enriched in Rappaport-Vassiladias (RV) broth (single enrichment) and plate d on XLT4 agar, Delayed secondary enrichment was performed, using single en richment broths that were stored for 4 days at room temperature. Results-Of 504 cultures, 186 (36.9%) Were Salmonella positive. A difference in proportions of samples with positive results was not found between same -day processing and storage at 4 C for 6 days. Compared with use of single enrichment for 24 hours (34% positive), use of DSE resulted in a greater pr oportion (40%; P < 0.001) of samples with positive results, Estimated relat ive sensitivities for the storage methods were 0.90, 0.85, and 0.71 for sam e-day processing, storage at 4 C for 6 days, and storage at -15 C for 14 da ys, respectively. Conclusions-Where practical, processing of fecal samples on the day of coll ection is recommended, although storage at 4 C for several days does not re sult in marked loss of sensitivity Improved detection associated with DSE w arrants further investigation and optimization.