Health authorities in the United Kingdom have issued a warning advising pregnant women and individuals with weakened immune systems to refrain from eating ready-to-eat (RTE) cold-smoked or cured fish. The caution follows a risk assessment conducted by the Food Standards Agency (FSA) and Food Standards Scotland (FSS), which reveals that these particular groups face a higher risk of severe illness from listeriosis. The assessment was prompted by an outbreak of Listeria infections linked to RTE cold-smoked fish.

Although the warning is specific to the UK, pregnant women and those with weakened immune systems in the United States, Canada, and Mexico, may also want to take note. 

Previously, smoked fish was flagged as a food of concern for vulnerable groups, with recommendations that pregnant women and individuals with weakened immune systems should consume it only after thorough cooking. However, the latest risk assessment has shed light on the seriousness of the risks associated with cold-smoked fish.

The investigation into the ongoing outbreak, initiated in October 2020, has yielded concerning results. There have been 19 linked cases of listeriosis in England and Scotland, leading to four fatalities. Most of the affected individuals are over 65 years old, but the outbreak also tragically affected one pregnant woman.

The risk assessment indicated that while the chances of contracting listeriosis from cold-smoked fish are low for higher-risk individuals, the severity of the illness is significantly high. This means that vulnerable groups face the potential for serious health consequences, hospitalization, and even death.

The assessment also pointed out several uncertainties, including the difficulty in estimating the infectious dose for Listeria monocytogenes and its variation among different vulnerable groups. The long incubation period of the bacteria complicates the attribution to a specific food source, as does the initial level of contamination and its multiplication through the food chain. Moreover, consumer behavior concerning use-by dates and temperature abuse also adds complexity to the issue.

Professor Robin May, the FSA's chief scientific adviser, emphasized the ongoing risk to health for specific vulnerable groups, and in light of the risk assessment, he advises those groups to avoid ready-to-eat cold-smoked and cured fish products.

Individuals with weakened immune systems include those with underlying conditions like cancer, diabetes, or liver and kidney disease. For these groups, the risk of severe infection, including life-threatening sepsis and meningitis, is higher.

Cold-smoked fish, such as smoked salmon or trout, and cured fish, such as gravlax, are not fully cooked during production, which means any Listeria present may not be eliminated. While cold-smoked fish is usually labeled as such on packaging, the processing type is often unclear. RTE cold-smoked fish is commonly found in thin slices and can be consumed cold. It may also be used in sushi.

Heat-treated smoked fish products, such as tinned smoked fish, are considered safe for consumption without further cooking. These products undergo high-temperature processing, which effectively kills Listeria.

The UK Health Security Agency (UKHSA) has identified 31 patients with links to eight smoked fish incidents between 2015 and June 2023, resulting in eight deaths and three cases associated with pregnancy. Despite the overall low risk to the general population, the cautionary advice aims to protect vulnerable groups from the serious consequences of listeriosis.