2.4.2. Botulism and other dairy products
Although rare (i.e., below 1% of the total incidences of reported foodborne botulism outbreaks), outbreaks of botulism have previously resulted from the consumption of contaminated cheese and other dairy produce (Collins-Thompson and Wood, 1992). One of these rare cases involved a jarred cheese product which contained 50 Mouse Lethal Doses (MLD) of type B toxin per gramme of cheese. Consumption of 70 g of contaminated product resulted, 3 days later, in the death of one individual . While other samples from the same batch were found to be contaminated with C. botulinum type B toxin-producing strain, no toxin production was detected, suggesting that the case of botulism resulted from incorrect storage of this product. Two outbreaks of botulism were reported to be the result of consumption of Brie ripened cheese in France and in Switzerland in 1973, arising due to the manner in which the cheese was stored during the ripening process. During this process cheeses were stored on straw contaminated with animal faeces. An outbreak of botulism in the United Kingdom in 1989 that resulted from the consumption of yoghurt containing type B botulinum toxin was reported , 27 cases in patients were identified, with 12 admitted into intensive care and one patient dying. The source was identified as hazelnut conserve that was used to flavour the yoghurt but which had not undergone sufficient heat sterilisation . The toxin concentration in the yoghurt was found to be within the range of 14–30 MLD/mL . In another instance, an outbreak of botulism in southern Italy, in which 8 people became ill after consumption of mascarpone or tiramisù, was attributed to a type A strain of C. botulinum . As a result of this outbreak a surveillance of mascarpone cheese in Italy was undertaken, which found that almost one third of the samples were positive for the presence of botulinum spores. The majority of isolates were also type A, with the remaining isolates identified as C. botulinum type B. It was concluded that the unusually high prevalence of botulinum spores in mascarpone could be attributed to both the high pH of the final product and ineffective processing (pasteurization and ultrafiltration) and storage practices. Finally, a French study published in 2004 focused on the presence of C. botulinum in raw ingredients used to manufacture processed foods, which are subjected to long term storage under refrigeration temperatures. It reported that over 10% of dehydrated dairy ingredients tested positive for the presence of C. botulinum. The analysis was carried out using PCR in combination with enzyme linked immunosorbant assay.