Abstract
On 9 October 2011, the University Hospital of North Norway alerted the Norwegian Institute of Public Health (NIPH) about an increase in Shigella sonnei infections in Tromsø. The isolates had an identical ‘multilocus variable-number tandem repeat analysis’ (MLVA) profile. Most cases had consumed food provided by delicatessen X. On 14 October, new S. sonnei cases with the same MLVA-profile were reported from Sarpsborg, south-eastern Norway. An outbreak investigation was started to identify the source and prevent further cases. All laboratory-confirmed cases from both clusters were attempted to be interviewed. In addition, a cohort study was performed among the attendees of a banquet in Tromsø where food from delicatessen X had been served and where some people had reported being ill. A trace-back investigation was initiated. In total, 46 cases were confirmed (Tromsø= 42; Sarpsborg= 4). Having eaten basil pesto sauce or fish soup at the banquet in Tromsø were independent risk factors for disease. Basil pesto was the only common food item that had been consumed by confirmed cases occurring in Tromsø and Sarpsborg. The basil had been imported and delivered to both municipalities by the same supplier. No basil from the specific batch was left on the Norwegian market when it was identified as the likely source. As a result of the multidisciplinary investigation, which helped to identify the source, the Norwegian Food Safety Authority, together with NIPH, planned to develop recommendations for food providers on how to handle fresh plant produce prior to consumption.
Highlights
IntroductionSymptoms are usually mild but range from watery, selflimiting diarrhoea to life threatening dysentery [1]
A case was defined as (i) a person in Norway with laboratory-confirmed S. sonnei infection after 1 October 2011 with the multilocus variable-number tandem repeat analysis (MLVA) profile identified in the outbreak with absence of travel history abroad, or (ii) a person who had an isolate with one-locus difference from the MLVA outbreak profile and an epidemiological link to (i)
All of them were admitted during the first days of the outbreak and had bloody diarrhoea; fever and abdominal pain, with a mean C-reactive protein of 234 mg/L
Summary
Symptoms are usually mild but range from watery, selflimiting diarrhoea to life threatening dysentery [1]. Of four Shigella species, S. sonnei is the most frequently isolated in industrialised countries [2]. Symptoms of S. sonnei infection are usually milder than those caused by S. dysenteriae or flexneri [3]. The bacteria are transmitted by ingestion of contaminated food or water, or through person-to-person contact. The incubation period ranges from 12 hours to one week [4]. The infective dose is very low: ingestion of 100 to 200 microorganisms can lead to disease [3]
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