Was the egg a plausible source for the Salmonella Potsdam outbreak?

Was the egg a plausible source for the Salmonella Potsdam outbreak? The paper, Outbreak of S. Potsdam associated with salad dressing at a restaurant (Commun Dis Intell 2003;27:508–512), implicated the egg as the 'most plausible source of S. Potsdam'. No tangible evidence to support this statement was provided and broader possibilities were not considered. The reasons for implicating the eggs were that another Salmonella serovar (Salmonella Infantis) was found on cloth used to clean the eggs and the egg was an ingredient common to the S. Potsdam positive dressings. Is the presence of one serovar in the environment an indication of the presence of another Salmonella serovar in the same environment? Unless a scien tifi c reference can support S. Infantis presence in environmental samples as an indicator for the pres ence of S. Potsdam, the scientifi c validity of the argument implicating the eggs is unsustainable. Was the egg the only ingredient common to all S. Potsdam positive dressings? Salad dressings were prepared by dividing a single batch of mayonnaise to make the fi ve salad dress-ings (p. 510). S. Potsdam was only found in two. This could indicate that the mayonnaise base was not the primary source but that the two salad dress-ings once they had acquired S. Potsdam through cross contamination from another source merely provided good media for multiplication. If the mayonnaise was the primary source, the main ingredient in the mayonnaise base was vegetable oil that in a kitchen with hygienic standards as described in the paper, could have been subject to cross contamination. Mayonnaise is prepared in restaurant kitchens by manual separation of the egg yolk and the white. Therefore, human hands were another possible common denominator. S. Potsdam has been isolated in Australia from potable water (J Powling, National Enteric Pathogens Surveillance System, personal communication). It does not appear that the water, a common denominator to all aspects of food preparation, was tested. The human cases 'ate a variety of food items' and 73 per cent of the human cases did not consume salad dressings or egg-containing food items. The paper, while acknowledging this discrepancy, argued that the kitchen practices were conducive to cross contamination and this could explain the occurrence of further cases in people that had not eaten food that contained eggs. Is cross contamination possible only from eggs to other food items? A timely and broader range of food sampling …