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Nr. 153: Sanitary survey rapport 11: Samsø Bælt

Larsen MM, Feld L, Jakobsen HH, Göke C, Hendriksen NB, Rømer JK, Mohn C, Jensen AN & Schultz AC. 2019. Sanitary survey rapport 11: Samsø Bælt. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 90 s. - Teknisk rapport nr. 153.  http://dce2.au.dk/pub/TR153.pdf


Regulation (EC) No 854/2004 of the European Parliament and the Council of April 29th, 2004 lays down specific rules for the organisation of official controls on products of animal origin intended for human consumption. Classification of production areas for live bivalve molluscs etc.[1] and the associated sampling plan are required to be based on so-called ‘sanitary surveys’. A sanitary survey is an assessment of the interactions between potential sources of microbial pollution, climate conditions and oceanography in the area. The EU Commission guidance for making a sanitary survey has formed the basis for this report. However, in certain cases, the Danish practice for microbiological sampling frequency and the previous classification on the basis of this is used. The Danish practice is described in ‘muslingebekendtgørelsen’, which is summarized in Appendix 11.

The report covers six production areas P92-P95, P210 and P217 situated in the Samsø Belt, between Jutland, Samsø and Zealand. In the area covering the Samsø Belt no permissions for mussel farming are registered. Likewise, few catches of mussels are recorded, with only landings from 2017 and 2018 registered during the last ten years, from P92 and P93.

The report is supported by publicly available data from monitoring of microbiological contamination in Samsø Belt where the concentrations of E. coli are determined in samples of mussels etc. taken at different sampling points within P92, the only production area where samples have been taken from 2009 to 2018. No samples for Salmonella have been registered. The report points to the most precautionary fixed sampling points for future monitoring. For the use of this report, data and information have been collected through homepages from e.g. municipalities and Statistics Denmark. Since these homepages are continuously updated, it cannot be guaranteed that the accessed data will be persistently available.

From the Danish surveillance of harvesting areas for mussels etc., a limited set of historical data is available for analyses of E. coli in mussels etc. collected from the Samsø Belt. During the last ten years (2009-2018), samples have been analysed from only one production area (P92), while the remaining five production areas are not represented in the sampling data. From the active production area, 56 samples have been analysed for E. coli and none have been analysed for Salmonella during the 10-year period. All samples were collected from the bottom and consisted of blue mussels (Mytilus edulis).

The data revealed a generally good microbiological hygiene in the investigated samples with all samples containing lower than 230 MPN E. coli/100 g. 43 samples (77 %) showed no detectable contents of E. coli (levels < 20 MPN E. coli/100 g). There were no sampling for Salmonella because this is on longer any required.

In summary, the sanitary survey of the Samsø Belt indicates a generally microbiologically clean area with no pronounced critical microbial contamination, but this could only be verified microbiologically for P92. For most of the individual production areas, no microbiological data exist, which prevents a statistical assessment of pollution from E. coli within the production areas, years or seasons. During the latest 3-year period (2016-2019), an adequate number of samples has been analysed from P92 allowing classification, whereas the other production areas reveal no analysed samples. Due to the limited amount of data, a comprehensive assessment of the hygiene status within the production areas is not possible. This implies that the impact of potential sources of pollution into the production areas cannot be satisfactorily evaluated.

This report recommends a microbiological sampling plan consisting of several designated sampling points and sampling frequencies for the individual production areas. It is further discussed whether merging of production areas into fewer areas could be an option in the future to reduce the number of sampling points, without compromising food safety.

Summary of recommended sampling programme

Based on an assessment of sources and transport routes for microbiological contamination (sanitary survey) verified as far as possible against historical microbiological data on the Samsø Belt, a microbiological monitoring programme is recommended for each of the production areas P92-P95, P210 and P217. In each of the recommended monitoring programmes, proposals for a sampling location, classification status (preliminary or permanent) and a sampling plan are outlined.

Based on the results from the sanitary survey of the production areas, supported by the historical data sets on the number, frequency and E. coli concentration in samples, it is assessed that only the production area P92 is considered suitable for permanent classification with a future sampling frequency of at least eight samples per year over a 3-year period. Assignment of a permanent classification is not possible for all the other production areas due to a lack of sampling in the past year (2018) and insufficient numbers of analysed samples (less than 24) within the past three years. If unclassified areas are to be upgraded to permanent classification, the EU guideline requires that the collection of data should include at least 12 samples for the latest six months or data from 24 samples over the last three years.

The report is divided into main chapters that provide a summary of identified microbiological contaminants. Appendices 2-8 serve as starting point of the main chapters. Appendix 9 is a detailed review of all historical microbiological data from mussel monitoring consisting of the fishery’s own-check and the Danish Veterinary and Food Administration’s[2] verification projects of the industry’s microbial monitoring. It was decided that a so-called ‘shoreline survey’ is unnecessary because all possible sources of sanitary contamination are described in the sewage plans for the cities in the area, the beach water quality monitoring and in the analyses of the Ministry of Environment and Food under the auspices of the Water Framework Directive.

[1] Include live bivalve molluscs, echinoderms, tunicates and gastropods.


[2] Fødevarestyrelsen.