Traces of the bacteria were found in an additional 12 patients, SSI said in a statement on Thursday. Two-thirds of those patients – eight in total – were previously treated with Dicillin before the multiresistant bacteria were detected.

The remaining four are still undergoing tests, according to the agency.

The discoveries mean that SSI has now found 25 people affected by the CPO outbreak, with 11 cases already registered.

The Danish Medicines Authority last month asked for persons using the antibiotic medicine Dicillin, produced by Sandoz, to return it to pharmacies to be replaced. That came after the multi-resistant bacteria known as CPO were detected in patients who had taken the antibiotic.

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None of the patients have suffered serious illness with the bacteria or received additional treatment, SSI said.

“This is not something that is dangerous for the individual patient. But we should naturally do whatever we can to prevent the spread of multiresistant bacteria,” medical director Tyra Grove Krause of SSI said in the statement.

Around 35,000 people were prescribed the antibiotic between September and December last year, according to Danish Patient Data Authority (Sundhedsdatastyrelsen) figures.

The number is potentially larger, as it was also sold after this period before the recall at the beginning of February.

CPO or carbapenemase-producing organisms are a group of bacteria that are resistant to several different types of antibiotics. They can be difficult to treat, according to information from the Danish Health Authority.

The risk of becoming seriously ill due to CPO is low for a healthy person, but people who are already ill or vulnerable can be at increased risk.

Infection with multiresistant bacteria can also mean all future hospital treatments for the affected person must be given in isolated rooms, so the bacteria are not passed on to other patients.

SSI first detected a particular CPO type which it had not previously seen in October last year. It initially suspected the bacteria could have spread at hospitals or been brought in via overseas travel before linking it to the antibiotic medicine Dicillin in February.

The Danish Patient Data Authority and SSI are now scrutinising how many people may have been exposed to the bacteria.

Krause previously told news wire Ritzau that “we have only seen the top” of the overall number.