Multi-country outbreak of Salmonella Enteritidis phage type 8, MLVA profile 2-9-7-3-2 and 2-9-6-3-2 infections

Salmonella Enteritidis, eggs, multi-country outbreak, multiple locus variable-number tandem repeat analysis (MLVA), Whole Genome Sequencing (WGS)
First published in EFSA Supporting Publications
10 March 2017
7 March 2017
Technical Report


A multi-country outbreak of Salmonella Enteritidis phage type (PT) 8 with multiple locus variablenumber tandem repeat analysis (MLVA) profiles 2-9-7-3-2 and 2-9-6-3-2, linked to eggs, is ongoing in the EU/EEA. Based on whole genome sequencing (WGS), isolates are part of two distinct but related genetic clusterS. ECDC and EFSA are liaising with relevant authorities in the Member States and the European Commission to facilitate the coordination of investigation and response measureS. From 1 May 2016 to 24 February 2017, 14 EU/EEA countries have reported 218 confirmed cases belonging to two distinct WGS clusters, and 252 probable cases sharing the S. Enteritidis MLVA profiles 2-9-7-3-2 or 2-9-6-3-2. Outbreak cases, both confirmed and probable, have been reported by Belgium, Croatia, Denmark, Finland, France, Greece, Hungary, Italy, Luxembourg, the Netherlands, Norway, Slovenia, Sweden and the United Kingdom. Eleven confirmed cases are reported to have travelled to Poland during the incubation period. Poland is therefore likely to be affected by this outbreak as well. Croatia and Hungary reported a fatal case each. The outbreak peaked at the end of September 2016, shortly before the vehicle of infection was identified and control measures were implemented at the farm and distribution level. Since then, the number of cases caused by the outbreak types of S. Enteritidis has steadily decreased: two or fewer new cases per week were reported in January and in the first week of February 2017. As of 24 February 2017, 21 confirmed and probable cases have been reported since 1 December 2016 by the United Kingdom (n=9), Norway (n=4), Belgium (n=3), the Netherlands (n=3), Hungary (n=1) and Sweden (n=1). The last case was reported by Norway, with the date of sampling being 2 February 2017. It is likely that contaminated food items were circulating in these countries until recently. The European outbreak case definition relies on a limited number of S. Enteritidis types (WGS for the definition of confirmed cases and MLVA for the definition of probable cases), and is therefore extremely specific. In countries where MLVA or WGS is not undertaken routinely, additional cases are expected to be associated with this outbreak. Available evidence from epidemiological, microbiological, environmental and tracing investigations identified eggs originating from three Polish packing centres as the vehicle of infection in this outbreak. Investigations in the farms identified 18 S. Enteritidis-positive laying hen farms in Poland. Most of these farms, as well as the three packing centres, belong to the same Polish consortium and are considered to be interlinked. According to information provided by Polish authorities, no S. Enteritidis-positive breeding flocks were detected in 2016. Based on the current evidence, the source of infection of this outbreak is likely to be at the level of the laying hen farmS. However, due to the nature of egg production there is the possibility that S. Enteritidis might have entered at a higher level in the food chain. It is therefore recommended that Poland conducts further checks on the S. Enteritidis status of the hatcheries and breeding flocks, especially those linked to S. Enteritidispositive farmS. In addition to the control measures already in place, it is recommended that Poland applies all measures that can reduce the risk of Salmonella contamination in laying hen farmS. In order to monitor the public health impact of control measures, an enhanced surveillance period has been established by the international outbreak investigation team. During the coming months, all countries should consider performing WGS on any human isolate characterised by MLVA profiles 2-9-7-3-2 or 2-9-6-3-2. ECDC will be offering WGS services to those countries that do not yet have WGS capacity in order to ensure that they can analyse human isolates linked to the outbreak. All countries identifying new confirmed or probable cases should also consider interviewing the new cases in a timely fashion. EU/EEA countries should also consider performing WGS on non-human S. Enteritidis isolates that have a link to the S. Enteritidis-positive farms in Poland. New cases and critical developments should be reported to EPIS-FWD (Epidemic Intelligence Information System for Food- and Waterborne Diseases and Zoonoses). The competent authorities in the food safety and the public health sectors in affected Member States and at the European level are encouraged to continue sharing information on the epidemiological, microbiological and environmental investigations, including issuing relevant notifications using the Rapid Alert System for Food and Feed (RASFF) and the Early Warning and Response System (EWRS), the latter representing the official channel to notify crossborder threatS.

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