A cluster of E.coli O157 infections in in South Yorkshire in the U.K. during 2019 was attributed to consumption of inadequately pasteurized from milk processed by a local dairy. Twenty cases were diagnosed of whom three developed hemolytic uremic syndrome. Traceback investigations identified the dairy as the source of infection. Assay of milk demonstrated showed defective pasteurization applying the phosphatase test.
Examination of the plant revealed a damaged rubber seal on a flow-diverter valve, allowing unpasteurized milk to contaminate effectively pasteurized product. The owners of the dairy were charged with an offense under existing food safety legislation and pleaded guilty to a series of offenses.
The outbreak strain of Siga-toxin producing E.coli (STEC) was isolated from fecal samples from cattle on the farm was supplying raw milk, although the causal organism as derived from patients was not recovered from available product.
Public health authorities noted, “Failure to detect the organism in a food vehicle does not provide evidence that the implicated vehicle is not the source of an infection. Detection of a pathogen in food samples should not be considered necessary to prove a link when the epidemiologic data provides good evidence of an association.”
Obviously, regulations in the U.K. provide more latitude for regulatory intervention than in the U.S. where demonstration of a pathogen in a product is generally required to order a recall and to substantiate either criminal action or civil claims.
In 1985 the Hillfarm Dairy in Melrose Park, IL., was implicated in an outbreak of Salmonella Typhimurium infection involving close to 3,000 confirmed cases and two fatalities. Although the specific cause was not identified it was suspected that contamination of post-pasteurized milk had occurred.
The failure of pasteurization in this dairy demonstrates the danger of raw milk that invariably contains pathogens derived from dairy cows, including STEC, Listeria, Campylobacter and Salmonella.