A warning has been issued in light of a food poisoning outbreak.
Cases of listeria monocytogenes - a bacteria that can cause the illness listeriosis - have been linked to smoked fish including salmon.
The outbreak is currently being investigated by the UK Health Security Agency, Food Standards Agency and Food Standards Scotland.
A total of six cases of listeriosis have been found since January this year across England and Scotland - including one case in a pregnant woman.
The illness can cause vomiting and diarrhoea and can be dangerous for elderly, vulnerable and pregnant woman.
Listeriosis can lead to miscarriage and even stillbirth in severe cases.
The bacteria is widespread in the environment and can contaminate a range of food at low or standard refrigeration temperatures.
It can be destroyed by thorough cooking.
It is of most concern in chilled, ready to eat foods that do not require further cooking, such as smoked fish.
Food Standards Agency head of incidents, Tina Potter, said: "Due to an outbreak of listeria monocytogenes linked to smoked fish, we are reminding people who are vulnerable to listeria infection - including people who are pregnant and people with weakened immune systems - of the risks in consuming smoked fish and asking them to make sure that the smoked fish is always thoroughly cooked including when served as part of a dish before they eat it.
"We are working closely with UK partners across government to ensure that this advice is as clear as possible - members of the public do not need to avoid these products, but should ensure risks are reduced as far as possible.
"You can do this by keeping chilled ready-to-eat smoked fish cold (5?C or below), always using products by their use-by date, following the storage and usage instructions on the label, and cooking or reheating smoked fish until it is piping hot right through."
What are the symptoms of listeriosis?
According to the NHS, listeriosis has no symptoms or only causes mild symptoms for a few days, such as:
- a high temperature of 38C or above
- aches and pains
- chills
- feeling or being sick
- diarrhoea
Listeriosis is not often serious and in most cases symptoms will clear after a few days.
However, there are some people who are more at risk of experiencing serious problems.
According to the NHS, high risk groups include:
- people who are pregnant
- newborn babies
- people aged 65 or over
- people with a condition that weakens their immune system, such as cancer, liver disease or kidney disease
- people having treatment that weakens their immune system, such as chemotherapy or steroid tablets
- people with diabetes who are unable to keep their blood sugar level down, even with treatment (uncontrolled diabetes)
Professor Saheer Gharbia, interim deputy director gastrointestinal infections and food safety (One Health) at UKHSA, said: "Listeria infection in most people is usually either unnoticed or may cause very mild gastrointestinal illness.
"However, it can have more serious consequences for some people, particularly those with pre-existing health conditions that cause weakened immunity, and people who are pregnant.
"There are certain foods that are more risky, and in light of this outbreak, we are advising pregnant and vulnerable people to thoroughly cook smoked fish before eating it.
"If you have any concerns about your health please speak to your midwife, GP or hospital specialist team."
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