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The use of Whole genome sequencing (WGS) identified a multi-country outbreak of human listeriosis associated with consumption of frozen sweet corn produced in Hungary. The purpose of this report was to summarise information on the cases occurring in the UK which were part of this outbreak and outline investigations on the presence of Listeria monocytogenes in the affected food chain. Prior to the international recall of this product in 2018, 12 UK cases of listeriosis were identified as infected by the outbreak strain between 2015 and 18. Epidemiological and microbiological investigations confirmed these cases as belonging to the outbreak. A further case occurred in 2019 and a contaminated frozen pack from one of the implicated batches of sweet corn was recovered from the patient's domestic freezer. The outbreak strain was also detected in products from a sandwich manufacturer in 2018 which added frozen sweet corn directly to sandwich fillings. The sandwich manufacturer's sweet corn was supplied by a distributor in England which obtained frozen products from the Hungarian manufacturer implicated in the outbreak. Within the distributor's premises, 208 food and environmental samples were taken: L. monocytogenes was detected in 44% of 70 samples of frozen sweet corn and 5% of 79 other foods. The outbreak strain was detected in the frozen sweet corn, in one other frozen food (mixed vegetables) and in the factory environment. The outbreak strain was also recovered from frozen beans on retail sale in the first four months of 2019. Five other L. monocytogenes strains together with two other Listeria species were detected in samples from the importer's premises. One of the L. monocytogenes strains in the importer's factory, which was distinct from the outbreak strain, was also recovered from sweet corn collected from the sandwich manufacturer, sweet corn tested in England in 2013 and 2016 and the blood of two cases of human listeriosis which occurred in England in 2014. This report shows how analysis by WGS provides evidence to understand complex food chains. This report also highlights risks for transmission of human listeriosis from frozen sweet corn and the potential for misuse of this food as a ready-to-eat product.

Cryptosporidium parvum and Cryptosporidium hominis isolates from sporadic, drinking water-associated, and intrafamilial human cases together with C. parvum isolates from sporadic cases in livestock were collected in the United Kingdom between 1995 and 1999. The isolates were characterized by analysis of three microsatellite markers (ML1, GP15, and MS5) using PCR amplification. Within C. hominis, four alleles were detected within the GP15 and MS5 loci, and a single type was detected with ML1. C. parvum was more polymorphic; 12 alleles were detected with GP15, 6 were detected with MS5, and 3 were detected with ML1. Multilocus analysis of polymorphisms within the three microsatellite loci was combined with those reported previously for an extrachromosomal small double-stranded RNA. Forty multilocus types were detected within these two species: 9 were detected in C. hominis, and 31 were detected in C. parvum. In C. hominis, heterogeneity was almost exclusively found in samples from sporadic cases. Similarity analysis identified three main groups within C. parvum, and the group that predominated in human infection was also found in livestock. Multilocus types of C. parvum previously identified only in humans were not detected in livestock. Isolates of both C. hominis and C. parvum from separate waterborne outbreaks were genetically homogeneous, suggesting preferential or point source transmission of certain types of these two species of parasites.