The United Kingdom has been hit hardest in a multi-country outbreak of Salmonella that has affected nearly 200 people.

Five European countries are investigating 192 Salmonella Mikawasima infections identified by whole genome sequencing (WGS).

As of Nov. 12, 138 people are ill in the U.K., 33 in Sweden, 18 in France, two in Denmark and one in Ireland. Most illnesses are non-travel related. The earliest date of illness onset is late August 2019.

Portugal has also recorded an increase of Salmonella Mikawasima in 2019, with most cases identified since August. WGS data for this year are not yet available for the isolates, which are under investigation.

ECDC confirms outbreak
Infections are more common in older adults than other age groups. Slightly more females than males have been reported.

Swedish officials initially revealed the outbreak and now the European Centre for Disease Prevention and Control (ECDC) has shared the number of people sick in other countries. The number of Salmonella Mikawasima cases in Sweden is usually one or two per year. All isolates are sequence type (ST) 1815.

ECDC reported that hypothesis-generation interviews are being done with patients in all countries. However, no robust hypothesis on the vehicle of infection has been found so far.

“This appears to be a multi-country outbreak taking place in a number of EU countries. The multi-country dimension has been identified through WGS analysis. However, the outbreak was also identified through exceedance analysis in the U.K., France and Sweden,” said ECDC officials.

“The close genomic relationship between isolates in the different countries indicates association with a common source. The lack of travel history for the cases and the recent identification possibly points to a vehicle of infection simultaneously distributed in different EU countries.”

ECDC and the European Food Safety Authority (EFSA) are also working on the third update to a multi-country outbreak of Salmonella Enteritidis linked to Polish eggs. It will be published by late January 2020.

The second update listed 1,412 cases associated with the outbreak: 532 confirmed and 166 probable infections since February 2017 and 343 historical-confirmed and 367 historical-probable cases between 2012 and January 2017.

Affected countries are Belgium, Croatia, Czech Republic, Denmark, Finland, France, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Poland, Slovenia, Sweden and the U.K. The U.K. has the most illnesses with 606, followed by 287 in the Netherlands and 187 in Belgium.

Source not identified
Salmonella Mikawasima ranked 34th of the serotypes reported in The European Surveillance System (TESSy). From 2014 to 2018, 17 EU countries recorded between 142 and 210 cases per year. Spain and the U.K accounted for 31 percent and 26 percent, respectively, of all confirmed infections.

Dr. Nick Phin, deputy director, national infections service at Public Health England, said the agency identified the outbreak using WGS.

“We are working with the Food Standards Agency, Public Health Wales and Health Protection Scotland to identify the source. There are simple steps to limit the spread of Salmonella, such as hygienic handling and preparation of food including cooking food thoroughly. Salmonella can also be spread from person to person, so anyone affected should adhere to good hygiene practice such as washing your hands thoroughly after using the bathroom,” he said.

Previous increases in Salmonella Mikawasima have been in late summer or autumn. WGS analysis found the current outbreak strain is not closely genetically related to any of the available strains identified in the previous years.

Last year, about 50 people in five European countries fell ill with the rare strain of Salmonella. Salmonella Mikawasima infected 15 people in Germany, 13 in Sweden, eight in both Denmark and the Czech Republic and six in Austria.

There was also an increase in the number of Salmonella Mikawasima infections in several EU countries in 2013. There has been an upward trend in Europe since 2009.

Symptoms of Salmonella infection can include diarrhea, abdominal cramps, and fever within 12 to 72 hours after eating contaminated food. Otherwise healthy adults are usually sick for four to seven days. In some cases, however, diarrhea may be so severe that patients need to be hospitalized.

Older adults, children, pregnant women and people with weakened immune systems, such as cancer patients, are more likely to develop a severe illness and sometimes life-threatening conditions.

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