Salmonellae in fish meal plants: relative amounts of contamination at various stages of processing and a method of control.

Previous studies have shown that Menhaden fish meal, a common ingredient of animal feeds, is frequently contaminated with salmonellae. Animals that eat contaminated feed may become infected. If they, in turn, are eaten by humans, they may be a means by which salmonellae are introduced into the human population. Epidemiological studies of the fish-meal industry were carried out to determine the sources of salmonellae in fish meal and the factors affecting the persistence and survival of salmonellae during the processing of fish meal. Examination of 190 fish immediately after they came from the Gulf of Mexico revealed no salmonellae, but salmonellae were frequently isolated from samples of fish taken from the boats when they arrived at the plants. Salmonellae were also frequently isolated from dockside water at each of the plants. Approximately 50% of the samples taken in the raw fish processing areas were contaminated with salmonellae. The percentage of samples yielding salmonellae decreased progressively through the various sequences of processing, but more than 15% of the samples taken from the finished products were also positive. Salmonellae were isolated from the raw area of the plant most frequently while the plant was operating and less frequently when the plant was idle, whereas in the processing area of the plant the reverse was true. Salmonellae appeared to survive and multiply in the processing area of the plant while the plant was idle, which resulted in contamination of the first portion of each day's production. Salmonellae in the processed fish meal were reduced to nondetectable levels by reprocessing the first 45 min of each day's production.