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No. 181: Sanitary survey report 12: West coast of Jutland (inner Wadden Sea)

Feld L, Larsen MM, Jakobsen HH, Göke C, Hendriksen NB, Rømer JK, Mohn C & Jensen AN. 2020. Sanitary survey rapport 12. Jyllands vestkyst (indre Vadehav). Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 104 s. - Teknisk rapport nr. 181. http://dce2.au.dk/pub/TR181.pdf.


Regulation (EC) No 854/2004 of the European Parliament and the Council of 29 April 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 five production areas P129 and P131-P134 situated by the West-coast of Jutland in the inner part of the Wadden Sea east of Rømø. In the area covering the West-coast of Jutland (inner Wadden Sea), no permissions for mussels farming are registered. Likewise no catches of mussels are recorded, because fishing for mussels in the Wadden Sea has been forbidden since 2008, e.g. due to the preservation of Natura 2000-areas and mussel-eating wading birds. Oyster safaris on the mudflats for tourists or locals have been common around both Fanø (P131, P132, P133) and Rømø (P134, P135 and P136), but have been stopped around Fanø due to several reports of norovirus symptoms from collected Pacific oysters in recent years. No reports have been found about norovirus from areas around Rømø.

The report is supported by publicly available data from monitoring of microbiological contamination in the area at the the West-coast of Jutland (inner Wadden Sea) where the concentrations of E. coli and Salmonella are determined in samples of mussels etc. taken at different sampling points within each production area. 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 web pages from e.g. municipalities and Statistics Denmark (Danmarks Statistik). Since these web pages are continuously updated, it cannot be guaranteed that the accessed data will be persistently available.

From the Danish mussel surveillance, a limited set of historical data is available for analyses of E. coli in mussels etc. collected from the the West-coast of Jutland (inner Wadden Sea). During the last 10 years (2010-2019), samples have been analysed from four production areas (P129, P132-P134), while the remaining production area (P131) is not represented in the sampling data. From the four active production areas, 89 samples have been analyzed for E. coli and 5 samples have been analyzed for Salmonella during the 10-year period. The majority of the samples analyzed for E. coli (70 samples) have been collected from P129, while from each of the areas P132, P133 and P134, only 6 samples, 10 samples and 3 samples have been collected, respectively. There are no active commercial production facilities within the area the West-coast of Jutland (inner Wadden Sea) and all samples were therefore collected from the bottom and from different species of mussels etc. Hence, 63 samples (71 %) consisted of common cockles (Cerastoderma edule), 26 samples consisted of oysters, of which 14 samples (16 %) were identified as Pacific oysters (Cras-sostrea gigas).

The overall data from the area the West-coast of Jutland (inner Wadden Sea) revealed a variable microbiological hygiene in the investigated samples with only 72 % of the samples (64 out of 89) at low levels ≤ 230 MPN E. coli/100 g, and no positive for Salmonella. During the last 3-year period, the corresponding amount of samples was reduced to 58 % of the samples (32 out of 55). Within the last 10 years, 25 samples from the total area showed increased concentrations of E. coli, and out of these, 24 samples showed levels of 230 < MPN ≤ 4,600 E. coli/100 g, and 1 sample showed concentrations of E. coli at levels of 4,600 < MPN ≤ 46,000 E. coli/100 g.

In summary, the sanitary survey of the West-coast of Jutland (inner Wadden Sea) identified a variable microbiological hygiene with transient occasions of microbial contamination. However, for most of the individual production areas, only a limited set of microbiological data exists, and data are not sufficient for classification of the areas, except for P129. The limited data material prevents a statistical assessment of pollution from E. coli within the production areas, years or seasons and a comprehensive assessment of the hygiene status within the production areas is not possible. This implies that documentation for the impact of potential sources of pollution into the production areas is not adequately present. The recommended sampling plan is thus prepared on basis of an expertise judgment of the presumed largest points of microbial pollution, where the sampling points are placed to represent potential discharge from these.

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 West-coast of Jutland (inner Wadden Sea), a microbiological monitoring programme is recommended for each of the production areas P129 and P131-P134. 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 individual production area P129 is considered suitable for permanent classification with a future sampling frequency of at least eight samples per year over a three-year period. Assignment of a permanent classification is not possible for all the other production areas due to lack of sampling in the past year (2019) and insufficient numbers of analyzed 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.