The current testing regime in England for unpasteurized milk is not fit for purpose, according to researchers describing a 2016 Campylobacter outbreak that sickened 69 people.
They say there was a need for regular microbiological monitoring to detect contamination with pathogens and recommended reviewing the legal testing criteria to include pathogen assessment, to ensure future outbreaks are prevented.
In December 2016, Public Health England investigated an outbreak of campylobacteriosis in North West England, with 69 infections during an 11-week period, according to the study published in the journal Epidemiology and Infection.
Epidemiological, microbiological and environmental investigations associated illness with drinking unpasteurized cows’ milk from Low Sizergh Barn Farm in Kendal, where it was mainly sold from a vending machine. About 70 liters of milk per day were sold via the machine.
Campylobacter was detected in milk samples which were identical to that isolated from cases. Investigations revealed the raw milk contamination had likely begun in late October 2016 with the first few cases developing symptoms in early November 2016.
Rules for pathogen testing
Sellers of raw drinking milk for direct human consumption must ensure the unpasteurized milk is routinely tested for coliforms and aerobic colony counts (ACCs). The requirements are a coliform count of less than 100 colony-forming units per milliliter (cfu/ml) and an ACC at 30 degrees C of less than 20,000 cfu/ml.
There are no legislative requirements for pathogen testing but it is encouraged by the FSA. Despite this recommendation, it is unlikely to be done routinely. If shelf life is five days or longer, there is a requirement to test for Listeria monocytogenes under European Commission Regulation No 2073/2005.
During the investigation, a bulk tank raw drinking milk sample complied with legislative standards, having ACC and coliform levels of 1,060 and 15 cfu/ml respectively, despite also containing Campylobacter jejuni. Researchers said current testing regimes appear to be inadequate to find pathogens and are not a failsafe.
Following the outbreak, a survey was done in Lancashire by PHE over four months in 2017. Despite only 59 samples, Salmonella Dublin and Campylobacter jejuni, and STEC O133:H4, which has an unknown pathogenicity, were detected. Coliform and ACC results were satisfactory, providing further evidence that legally compliant samples are poor indicators of the presence of pathogens, according to researchers.
Data from Public Health England show that in England and Wales, between 1992 and 2002, there were 17 outbreaks of gastroenteritis reported that were linked to raw drinking milk. Six outbreaks were reported between 2014 and 2017; implicated pathogens included Shiga toxin-producing E. coli O157, Salmonella Dublin and Campylobacter spp.
Regulations restrict raw drinking milk sales in England, only permitting them from a producer directly to the final consumer, with an equivalent law in Wales and Northern Ireland. Legislation in Scotland prohibits the sale of unpasteurized drinking milk.
Ill people aged one to 74 years old
Researchers also said a required warning label should emphasize the risk to vulnerable groups. The FSA ran a comment period on proposed enhanced controls for production of raw milk in 2019. Responses have just been published.
In England, raw milk containers must display: “This milk has not been heat treated and may therefore contain organisms harmful to health”. In Wales, as well as that sentence labels must also say: “The Food Standards Agency strongly advises that it should not be consumed by children, pregnant women, older people or those who are unwell or have chronic illness.”
The farm started selling raw drinking milk in March 2016. It had a café and farm shop in which raw milk was served and it was also sold via an outdoor self-service vending machine.
Duration of illness was from 1 to 32 days. The age of cases ranged from 1 to 74 years old. Onset dates of symptoms were from Nov. 3 to Dec. 25, 2016, but no one was hospitalized.
There were 16 laboratory-confirmed cases of Campylobacter jejuni. Two raw milk samples from the farm were positive for Campylobacter jejuni: one bottled sample from the self-service vending machine and one from the raw milk bulk tank.
The farmers own testing results had been unsatisfactory but this was not reported to FSA, according to Public Health England.
During a visit in December 2016, control methods were reviewed and the farm was told to suspend raw milk sales on a voluntary basis.
Environmental swabs from the milking parlor on Dec. 22 and the water sample from the bore hole tested negative for pathogens. Nine clearance raw milk samples from the bulk tank one week later were negative for Campylobacter spp. but positive for STEC O157 and Listeria monocytogenes.
A follow-up inspection in March 2017 noted improvements and dairy hygiene conditions were deemed satisfactory. Also, by this time three sets of raw milk clearance samples had been obtained and all of them were negative for pathogens.
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