Microbiological quality of raw drinking milk and unpasteurised dairy products: results from England 2013–2019

Abstract

The aim of this study was to review microbiology results from testing >2500 raw drinking milk and dairy products made with unpasteurised milk examined in England between 2013 and 2019. Samples were collected as part of incidents of contamination, investigation of infections or as part of routine monitoring and were tested using standard methods for a range of both pathogens and hygiene indicators. Results from testing samples of raw cow's milk or cheese made from unpasteurised milk for routine monitoring purposes were overall of better microbiological quality than those collected during incident or investigations of infections. Results from routine monitoring were satisfactory for 62% of milks, 82% of cream, 100% of ice-cream, 51% of butter, 63% of kefir and 79% of cheeses, with 5% of all samples being considered potentially hazardous. Analysis of data from cheese demonstrated a significant association between increasing levels of indicator Escherichia coli with elevated levels of coagulase positive staphylococci and decreased probability of isolation of Shiga toxin-producing E. coli. These data highlight the public health risk associated with these products and provide further justification for controls applied to raw drinking milk and dairy products made with unpasteurised milk.

The use of alkaline phosphatase and possible alternative testing to verify pasteurisation of raw milk, colostrum, dairy and colostrum‐based products

“…However, L. monocytogenes was detected in three samples of goats' milk and one of sheep milk. Willis et al (2018) and McLauchlin et al (2020) both found that, while pathogens were detected in raw sheep and goats' milk, the microbiological quality of raw cows' milk was poorer than for other species. Verraes et al (2014) undertook a review of the scientific literature relating to the prevalence of pathogens in raw milk of species other than cows.…”

Response to the Specialist Cheesemakers Association on ‘Microbiological quality of raw drinking milk and unpasteurised dairy products: results from England 2013–2019’

“…We thank Percival and colleagues for their comments on response to our paper ‘Microbiological quality of raw drinking milk and unpasteurised dairy products: results from England 2013–2019’ published in Epidemiology and Infection in May of 2020 [ 1 ]. Following an e-mail correspondence with Dr Percival in 2020 which covered similar ground to that in the letter, two of us (CW and JMcL) virtually met with Dr Percival in October 2020 to discuss her concerns.…”

“…Within the published paper [ 1 ], we have acknowledged sources of bias in the data presented, and separately described microbiological results generated from samples collected during incidents and outbreaks as compared to those from routine monitoring. We also restricted data to those from testing samples of final product at the point of production and to products during sale: results were not considered from samples collected during production including those of food ingredients.…”

“…We reported results from testing cheese made from unpasteurised milk and demonstrate an association between detection of elevated levels of E. coli and both elevated levels of coagulase-positive staphylococci, as well as the detection of Shiga-toxin genes, but not with the isolation of L. monocytogenes [ 1 ]. Although conceding that generic E. coli as an indicator can be an imprecise tool, we did not enter into speculation as to the mechanisms for these associations.…”

“…Despite the public health risks associated with the consumption of unpasteurised milk and products made from unpasteurised milk, it was not our intention to ‘chastise an entire industry’ but to protect public health. There is a common goal to improve the microbiological quality of these products and we would welcome a peer reviewed publication by Percival and colleagues using the considerable quantity of industry data that must be available amongst members of the SCA which may elucidate further the observations and associations we made in 2020 [ 1 ].…”