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Salmonella

Mayonnaise, both commercially processed and home-made, has been associated with illnesses from Salmonella globally. The source of the Salmonella has been confirmed to be raw eggs. Several outbreaks with fatal cases have been recorded, with a few major incidents. In a 1955 outbreak in Denmark, 10,000 people were affected by Salmonella from contaminated mayonnaise made by a large kitchen. The pH of the mayonnaise was found to be 5.1, with Salmonella counts of 180,000 CFU /g. The second outbreak, also in Denmark, caused 41 infections with two fatalities. The pH of the contaminated mayonnaise was 6.0, with Salmonella counts of 6 million CFU/g. In 1976 there were serious salmonellosis outbreaks on four flights to and from Spain which caused 500 cases and 6 fatalities. In 1984 in the US, 404 people became ill and nine died in a New York City hospital due to hospital-prepared mayonnaise. In all salmonellosis cases, the major reason was inadequate acidification of the mayonnaise, with a pH higher than the recommended upper limit of 4.1, with acetic acid as the main acidifying agent. Some brands use pasteurized eggs which would reduce this risk factor.