British tourists visiting France are being warned after five people were hospitalised after eating a common sauce.

The three women and two men, who are all in their 30s, are suffering with botulism after a birthday meal in the Indre-et-Loire region.

The condition, which the NHS says can be fatal in 5 to 10 percent of cases, attacks the nervous system and can cause paralysis.

The group are believed to have consumed the bacteria that causes botulism, Clostridium botulinum, after eating contaminated pesto.

French authorities believe around 600 jars of the pesto, made by the O Ptits Oignons brand, may be contaminated – and anyone who has purchased them is urged not to eat them. 

According to French newspaper Le Monde, four of those contaminated presented themselves to hospitals on Saturday last week, with the fifth arriving the next day.

It is believed the 600 jars of contaminated pesto could be anywhere throughout France, and people who have them are advised to dispose of them without opening them.

Some of the jars may have been sold some months ago, the French national reports, however the symptoms of botulism tend to develop within hours to days after infection.

French authorities have urged anyone who starts showing signs of infection to seek medical advice immediately.

In a statement online, O Ptits Oignons said the company was “sincerely sorry” to those who were in hospital.

According to the NHS, initial symptoms include feeling sick, vomiting and diarrhoea or constipation.

Without treatment, botulism can begin to cause paralysis, with symptoms including facial muscle weakness, blurred vision, drooping eyelids, slurred speech and breathing difficulties.

NHS guidance states that food-borne botulism occurs after people eat contaminated food that has not been “properly canned, preserved or cooked”.

It adds: “Clostridium botulinum bacteria are found in soil, dust and river or sea sediments.

“The bacteria themselves are not harmful, but they can produce highly poisonous toxins when deprived of oxygen, such as in closed cans or bottles, stagnant soil or mud, or occasionally, the human body.”

“Botulism is a serious condition that requires immediate medical attention.

“Go to your nearest A&E department or immediately dial 999 if you or someone you know has symptoms of botulism.

“Treatment is more effective the earlier it’s started.”