The increase in cases of Salmonella enterica serotype Goldcoast infection was observed during September, with symptom dates between 21 June and 6 October 2013.
Of the 38 cases, 10 were hospitalised and four were admitted to intensive care, the median duration of illness was 13 days.
The outbreak was investigated by the UK Food Standards Agency (FSA), which found the link between the consumption of whelks from independent shops, market stalls and mobile seafood vans, largely in East Anglia.
Lynn Shellfish Ltd of King’s Lynn (formerly known as Heiploeg or Heiploeg and Lynn Shrimpers) issued a recall of batches of frozen and chilled whelk, which is a name applied to kinds of sea snail.
Whelks have been associated with toxin-based food poisoning but this was the first known report of bacterial food poisoning associated with whelk consumption.
Whelks are processed by cooking in a pressure cooker, their shells are crushed and removed before the meat is cooled in a water bath.
A small proportion is sold fresh, with the majority of cooked whelks being flash frozen before sale.
Inns et al said epidemiological, environmental, microbiological and food chain evidence supported findings that the outbreak was associated with product processed by the same factory.
During September, 17 laboratory-confirmed cases of infection with gastroenteritis were reported in England. This was greater than the annually expected number: in 2012, eight cases in England, in 2011, five and in 2010, 13.
Presumptive Salmonella isolates were screened using a real-time polymerase chain reaction (PCR) assay for identification of the most common subspecies of S. enterica.
Public Health England started investigating on 12 September to identify the outbreak source and enable control measures to prevent further cases. The last case, with symptom onset in October, was reported on 12 November.
The cases’ ages ranged between six months and 83 years (median: 64 years); two were aged under 16 years.
Of the 38 cases, 25 were male and all were resident in England, predominantly in the east of the country.
Environmental health officers visited the production factory on 20 September and cooking temperatures could not be verified and the production of ready-to-eat whelks was stopped.
In a second inspection on 23 September, inadequate product temperatures were recorded immediately following cooking and the whelks processed on that day and stored frozen on the premises were kept on the site.
Microbiological evidence suggests that production equipment in contact with cooked whelks was contaminated with Salmonella Goldcoast for a number of weeks, despite the use of a sanitiser and the cooked whelks passing through a highly saline bath, said the researchers.
One of the environmental samples that tested positive was a swab of the conveyer belt used to transport raw whelks to the cooker, indicating that it was present on at least some whelks before entering the factory.
Salmonella Goldcoast outbreaks have been associated with pork products (salami, pork cheese (cooked pig organs stuffed in a pig stomach), French paté and raw fermented sausage, watercress and hard cheese.
“Outbreak of Salmonella enterica Goldcoast infection associated with whelk consumption, England, June to October 2013”
Authors: T Inns, G Beasley, C Lane, V Hopps, T Peters, K Pathak, R Perez-Moreno, G K Adak, A G Shankar