A Salmonella outbreak in Norway has expanded with 23 people now potentially affected.

The Norwegian Institute of Public Health (Folkehelseinstituttet) said the patients, aged between 2 and 91 years old, became ill in January and February.

Salmonella Agbeni has infected 11 people with another 12 suspected cases. The outbreak announcement last week revealed nine people were sick. An investigation to find the source is continuing with local authorities, the Veterinary Institute (Veterinærinstituttet) and Norwegian Food Safety Authority (Mattilsynet).

Including confirmed and suspected cases, 10 men and 13 women are ill. Patients live in Oslo, Akershus, Buskerud, Østfold, Vestfold, Vest-Agder, Rogaland, Møre og Romsdal, Trøndelag and Nordland.

Officials at the Norwegian Institute of Public Health say they suspect people became infected with Salmonella through a food or foods that are widely distributed. Interviews are being conducted with patients and samples of food taken to find the source of infection.

Lab analysis is ongoing to confirm the suspected infections while bacteria with a similar DNA profile has been detected in confirmed cases, which suggests a common source.

Officials from the Norwegian Institute of Public Health said investigations can take time with no guarantee the source of infection will be found. They added it was too early to say whether it is a limited outbreak or if additional patients will be identified.

Between 900 and 1,300 cases of salmonellosis are reported to the agency each year with the majority infected while traveling abroad.

Salmonella Agbeni was not in the 20 most frequent serovars in confirmed cases of human salmonellosis in Europe meaning there were fewer than 265 infections in 2017, according to data from the European Food Safety Authority (EFSA).

People can experience symptoms of Salmonella infection between six and 72 hours after exposure and these usually last for three to seven days. They include fever, diarrhea, vomiting, headaches, stomach cramps and loss of appetite. More severe symptoms may occur in young children, older people, pregnant women and people who are immunocompromised.