The first case was reported with onset of symptoms on 24 December 2014 and the latest count includes data up to 31 July.
More than half of the patients (113) fell ill after eating at a restaurant linked to using Iwi spice mix sold by the company Dimpex. Another firm, Sevan, issued a withdrawal after Salmonella was found in some of its already opened products but it is not part of the restaurant outbreak.
Each year, two to five cases with Salmonella Enteritidis phage type (PT) 13a are reported. In 2014, four of the domestic S. Enteritidis cases were PT 13a, according to the research in Eurosurveillance.
Minor increase could go unnoticed
Sweden launched an ‘urgent inquiry’ in the Epidemic Intelligence Information System (EPIS), on 2 April. No other country has reported an increase of this specific subtype of S. Enteritidis.
However, many European Union Member States only subtype S. Enteritidis in outbreak situations or cluster investigations and phage typing or MLVA is not performed in all EU countries so a minor increase could go unnoticed.
A Rapid Alert System for Food and Feed (RASFF) alert by Austria on 26 June reported Salmonella spp. in a spice mix/seasoning from a manufacturer in Croatia, with a similar content of dried vegetables as one of the brands implicated in the Swedish outbreak.
Batches of this product, distributed to Austria, Germany and Slovakia, were recalled by the manufacturer. The specific batch from which Salmonella spp. was detected was not distributed to Sweden.
The serotype was S. Oranienburg (not S. Enteritidis PT 13a), according to the Austrian Salmonella Reference Centre.
“In countries with a high number of reported cases of S. Enteritidis infection, however, a small increase in number of cases with the outbreak strain could go undetected,” said the report.
“The detection of Salmonella spp. in two different brands of spice mixes sold in Sweden and the RASFF alert from Austria during the outbreak period, however, indicates that there could be a common ingredient in these mixes that could be contaminated with Salmonella spp.”
Initial investigations suggested the vehicle of infection was most likely a food item with a long shelf life given the first case was reported in December.
By the end of May cases had risen to 48 and were from over 14 counties.
At the beginning of June, Kalmar county reported a case who had fallen ill after eating at a restaurant, cases continued to be reported and at the end of the following week six people were ill.
As they all shared the strain, they could be connected to the S. Enteritidis PT 13a outbreak.
In total, 108 cases were connected to the restaurant, including staff members. Many had severe symptoms, including bacteraemia, and were hospitalised but exact numbers are not yet verified, said the report.
On 9 July, the laboratory at the National Veterinary Institute (SVA) in Uppsala, detected a Salmonella isolate in an unopened package of a spice mix from the restaurant originating from Serbia, containing dried vegetables, e.g. onions, carrots and parsnips.
Two spice mix samples of another brand, manufactured in Bosnia and Herzegovina and Serbia, came from opened packages from two different households in Sweden.
One had one of the profiles seen in the ongoing outbreak while the other did not. When an opened package is found positive, it could mean it was contaminated after opening.
Phage typing has been the gold standard for subtyping of S. Enteritidis; however, multiple-locus variable-number of tandem-repeats analysis (MLVA) was set up, enabling further subtyping of isolates. Whole genome sequencing as a first-line tool for typing is under development.
During analysis of food items, and specifically spice mixes, it was found a more sensitive method than the commonly used Nordisk Metodikkommitté för Livsmedel (NMKL) number 71 method, corresponding to International Organization for Standardization (ISO) 6579:2002/Corr 1:4, could be needed.
Additional dilution steps and number of replicates were often necessary to detect and isolate Salmonella spp., indicating very low concentration of the pathogen in spices.
“Outbreak of Salmonella Enteritidis phage type 13A infection in Sweden linked to imported dried-vegetable spice mixes, December 2014 to July 2015”
Authors: C Jernberg, M Hjertqvist, C Sundborger, E Castro, M Löfdahl, A Pääjärvi, L Sundqvist, E Löf