A Salmonella outbreak initially reported in Norway has grown and now is also affecting Sweden.

The Norwegian Institute of Public Health (FHI) said 58 people are sick in the Salmonella Agona outbreak and 23 had been hospitalized. This is up from 31 sick and 13 hospitalizations.

In Sweden, 26 people have been affected, according to the Public Health Agency of Sweden (Folkhälsomyndigheten).

Norwegian situation

In Norway, people in 10 regions were diagnosed with infections from Nov. 7 to 29 with a peak in the middle of the month. Salmonella Agona is a rare type of Salmonella in Norway and Europe.

Those sick are aged 1 to 88 years old and 27 of them are women. Bacteria with the same genetic profile, meaning they were likely infected by the same source, have been detected in 37 of 58 patients. For the other 21, sequencing results from laboratory tests are pending.

The majority of sick people live in Viken, followed by Vestland and Vestfold og Telemark. Single-figure patient numbers have been recorded in Innlandet, Trøndelag, Troms og Finnmark, Møre og Romsdal, Oslo, Rogaland, and Nordland.

Source of the outbreak not yet known
An investigation to find the source is ongoing with FHI, local officials, the Norwegian Food Safety Authority (Mattilsynet), and the Veterinary Institute. The cause is believed to be an imported food product distributed across the country and also in Sweden.

Heidi Lange, from FHI, said patients are being interviewed to see if there is a common source of infection.

“In addition, we also collect information from purchase receipts in cooperation with the Norwegian Food Safety Authority and the grocery industry. We do this because it can be challenging to remember everything that was eaten before illness,” she said.

“FHI plans to carry out a case-control study. This involves comparing what patients have eaten with what a random selecion of other people have eaten within the same time period. In this way, we can test out various clues about the source of the outbreak, and whether there is an increased risk of disease linked to certain foods.”

In Sweden, 26 people have fallen ill since the start of November. Patients range in age from 3 to 86 years old and are from 12 different regions in the country. Fifteen cases are women.

Whole genome sequencing has shown they have the same type of Salmonella Agona, so are suspected of having been infected by a common source.

Folkhälsomyndigheten, local infection control units, and the Swedish Food Agency (Livsmedelsverket) are helping Norwegian authorities to search for the source of the outbreak.