Shigella from sugar peas in Scandinavia

The peas apparently came from Kenya. But that wouldn’t fit the alliteration.

Eurosurveillance reports that in Norway, shigellosis is a mandatorily notifiable disease, and all isolates are submitted to the NIPH for verification and typing. Around 150 cases of shigellosis are confirmed per year, the majority caused by Shigella sonnei. Only around 10 to 20 of the shigellosis cases reported each year are acquired in Norway, usually as secondary cases caused by faecal-oral transmission in households.

An outbreak investigation was initiated on 27 May by interviewing the four confirmed cases using a trawling questionnaire. On the same day the NFSA inspectors visited the two households where suspected cases were reported and found an unopened package of sugar peas imported from Kenya in one household, and the packing of the same brand of sugar peas in the other. The sugar peas were bought in the same shop. Based on this suspicion, it was decided to focus the interviews on consumption of fresh vegetables and lettuce.

By 16 June, the reference laboratory has registered a total of 20 cases with the outbreak strain of Shigella sonnei, who had not travelled abroad prior to illness onset. The cases live in different municipalities, but mainly in the central and western parts of Norway. The date of onset for the first case was 10 May. All cases were adults except for one teenager, and 16 of them were women. All 20 cases reported to have eaten sugar peas, and there were no other obvious common exposures identified. The majority of the patients had bought the sugar peas in one of the large supermarket chains and only a few in another chain. The NFSA traced the suspected food product and found that all the implicated sugar peas were produced in Kenya. One sample from the unopened package of sugar peas collected in a patient household was positive for Shigella sonnei by both PCR methods, but could not be culture-confirmed.

As a response to our urgent inquiry Denmark reported an increase in the number of domestic Shigella sonnei infections in April and May 2009. They initiated an outbreak investigation to find out if the Danish cases were related to the outbreak in Norway. The investigation in Denmark also pointed at sugar peas as the source of the outbreak, and microbiological investigations (including MLVA typing) to compare the outbreak strains are ongoing.