Salmonella contamination in commercial eggs and an egg production facility

Egg samples were collected from various stages of an egg processing operation and from the attached production facility. Salmonella was isolated from 72.0% of all samples collected from the laying house environment. Recovery of Salmonella from flush water, ventilation fan, egg belt, and egg collector samples were (positive samples/total samples collected): 2/2, 4/4, 16/22, and 14/22, respectively. Salmonella was found on 7 of the 90 eggshells sampled before processing and 1 of 90 eggshells sampled after processing, but Salmonella was not found in the 180 eggs analyzed for internal contamination following processing. The one eggshell found positive for Salmonella following processing was detected when the pH of wash water samples was lowest (10.19). The 60 isolates from production facilities included the following Salmonella serotypes: S. agona, S. typhimurium, S. infantis, S. derby, S. heidelberg, S. california, S. montevideo, S. mbandaka, and untypable. The 22 isolates obtained from eggshells prior to processing were serotyped as S. heidelberg and S. montevideo. All five isolates obtained from eggshells after processing were serotyped as S. heidelberg. These data suggest that although the shells of about 1% of commercial eggs are contaminated with Salmonella, contamination of the internal contents of eggs with Salmonella is a rare event.