The bacteria in question is a rare form known as Salmonella Coeln, but the source is so far unknown.

People across the country have been affected by the outbreak, with a total of 13 women and 10 men so far confirmed ill, with half of those hospitalized after being infected, Ritzau reported on Tuesday afternoon.

“This is a (bacteria) type we don’t often see, maybe two to five cases yearly. So when 23 cases show up in one month, that’s an unusual situation,” said senior researcher Steen Ethelberg of the SSI disease research institute in Copenhagen.

The actual number of people to have been infected is likely to be higher than 23, Ethelberg added.

“We only register the sickest: people who go to the doctor and test positive for salmonella. We normally say there are 10 times as many who we don’t know about,” the researcher said.

SSI is now working together with the Danish Veterinary and Food Administration (Fødevarestyrelsen) and the Technical University of Denmark’s National Food Institute to find the source of the bacterial outbreak.

“We are interviewing the sick and asking where they have been and what they have eaten. We’re usually able to find a pattern. But with this outbreak, it’s not yet been possible to find a common factor, so we’re continuing the investigation,” Ethelberg said.

The affected individuals had not been abroad immediately prior to being taken ill, are located in different parts of the country, do not know each other and have not taken part in any common event.

That makes it likely that a widely-distributed food product is the cause of the outbreak.

Salmonella Coeln was described by Ethelberg as neither better nor worse than other types.

“You don’t get more sick from Salmonella Coeln than with other types of Salmonella,” he said.

Symptoms of infection by the bacteria include diarrhoea, stomach pains, fever, headache and possibly nausea and sickness. Illness can last from a few days to several weeks.

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