Microorganisms and parasites were only rarely detected in seafood products imported to Norway from third countries in 2018, according to a new report.

The document summarizes an ongoing monitoring program for veterinary border control on seafood products imported to Norway from countries outside the EU and European Economic Area in 2018.

The Institute of Marine Research (IMR) carried out analytical work on behalf of the Norwegian Food Safety Authority (Mattilsynet), and personnel at Norwegian Border Inspection Posts (BIPs).

A total of 122 samples from Mattilsynet, collected at BIPs, were examined for microorganisms, parasites and undesirable chemical substances. Microbiological analyses were performed on 104 samples.

Listeria and Vibrio

Results for microbiological indicator organisms for fecal contamination were mostly below detection limit or had low bacterial counts. However, higher counts were found in one sample of Yellowfin tuna imported from the Maldives and one Pacific cod from Thailand.

Listeria monocytogenes was detected at a low level in a sample of Pacific cod from Thailand and one Norwegian herring re-imported to Norway from Egypt.

Vibrio spp. was qualitatively detected in two of 21 samples; one a whole, headless scampi from Vietnam, and the other peeled, headless scampi from India. The strains isolated from these two samples were identified as Vibrio cholerae and Vibrio parahaemolyticus respectively. One sample of Eastern Oysters from Canada was examined for E. coli and less than 18 bacteria per 100 gram sample material was found.

Parasite prevalence

Yeast and mold was found in one sample of dried Yellow Stripe Trevally from Thailand and in Migas from China. The two highest histamine values of 20 and 30 milligram per kilogram wet weight were found in samples of Peruvian anchovy.

Parasitological examination on 40 fish samples found nematodes in nine of them. Since fish were imported frozen, nematodes were dead and not infective. The highest numbers of nematodes (21), were found in a sample of Atlantic cod imported from Russia.

Two samples of Pandalus shrimp from Russia, were measured with relatively high arsenic concentrations of 140 and 170 mg/kg ww. For lead, one sample of small crabs from Thailand was measured to 0.69 mg/kg ww. A sample of canned sardine in oil from the Philippines, exhibited a cadmium value of 0.1 mg/kg ww, above the maximum level.

Reduce risk of shellfish contamination

Meanwhile, researchers in New Zealand have looked at methods shellfish growers use to reduce the risk of norovirus.

The virus is the top cause of foodborne illness worldwide and in New Zealand there have been outbreaks linked to commercially grown and imported shellfish. With the growing population and likely increase in demand for shellfish, the issue is projected to escalate, with potentially negative effects on the shellfish industry in the country.

Shellfish such as oysters, mussels and clams can accumulate norovirus when they are exposed to contaminated water.

The Institute of Environmental Science and Research (ESR) scientist Joanne Hewitt, co-author of the study, said growers in New Zealand have a range of methods before and after harvest to mitigate and manage risk.

Testing for fecal indicator bacteria such as E. coli is a common way to identify risk prior to harvesting. In New Zealand, guidelines are based on concentrations of E. coli in shellfish and fecal coliforms in water.

Pre and post-harvest measures

The study, involving scientists from ESR and Plant and Food Research – a New Zealand-based science company – found standard guidelines using fecal indicator bacteria do not necessarily predict a risk of norovirus contamination in water and shellfish.

Dr. Hewitt said the main reason for this is that norovirus can remain infectious in shellfish flesh for weeks following contamination, unlike indicator bacteria, that are rapidly removed from shellfish or die-off in the marine environment.

She added while industry and authorities are trying to prevent illegal discharges of human sewage from boats and septic tanks, scientists recommend better microbial source tracking to identify and reduce the risk, especially for shellfish consumed raw.

The study found that while pre-harvest preventative measures are preferable, post-harvest interventions can be used to mitigate risk. Current post-harvest methods such as depuration, relaying, thermal and high-pressure processing all have limitations, so the choice should be based on environmental, economic and social factors.

Contamination risks can be managed by preventing inadequately treated wastewater being discharged into the environment, making sure harvesting does not take place for a time after incidents and locating shellfish farms more than 10 kilometers from possible sources of contamination.