Folkhälsomyndigheten (The Public Health Agency) said illnesses are between October 2017 and March this year.
The agency added during autumn and winter several domestic cases of S. Kentucky have been reported and authorities are trying to identify a possible common source of infection.
The source has not been identified but is believed to be foodborne.
In recent years, Sweden has reported annually one to six cases of S. Kentucky.
Difficult outbreak investigation
The majority of cases are in Västra Götaland (37), Uppsala (nine), Stockholm (seven), Kronoberg (four), Skåne (three) and Värmland (three).
Median age of cases is 85 with a range from 30 to 98 years and 68% of ill cases are women.
Folkhälsomyndigheten told FoodQualityNews that since the majority of cases do not have a date for onset of disease it is ‘virtually impossible’ to establish an epidemiological time line.
“Also, as the Salmonella infection seems to be quite mild it may have contributed to a delayed sampling. For this reason a case-control study has not been considered feasible,” said the agency.
“Moreover, the cases are spread in six different counties in Sweden and more than one hospital or nursing home in each county have cases. Hence, we think the source is most likely foodborne.
“Still, based on the dates for hospitalization we have identified a time period where it is likely that the cases got infected. A questionnaire has been sent out to all kitchens serving hospitals and nursing homes with cases to identify what foods they have in common. Several foods have been analysed.”
Analysis results negative
Livsmedelsverket (National Food Agency) told us that it has coordinated work performed by other authorities and stakeholders as well as analysing some of the samples taken.
“This has been a very difficult outbreak to investigate, and we have not been able to identify the source of infection. Samples of several food types have been analysed, e.g. liquid nutritional supplements, protein energy powders, purées, dry spices, frozen herb spices, frozen fruits and berries. All analysis results are negative.”
Folkhälsomyndigheten said for the vast majority of cases there is no clear onset date due to their precondition or because the salmonellosis has passed asymptomatic.
“All but two of the cases are old and/or very sick, with co-morbidity, and the Salmonella infection seems to be quite mild. Therefore, hospitalisation and death among the cases may primarily be due to other factors than the Salmonella infection.
“Almost all cases have recent hospital care or stay in nursing home prior to or during testing positive for Salmonella infection. The remaining cases are staff in nursing homes (two cases) or elderly living at home with food delivery from home care (two cases).”
Some hospital kitchens have voluntarily imposed restrictions on certain foods but since there are no cases authorities are confident where infected in 2018 most restrictions are, or soon will be, lifted.
All isolates from cases analyzed to date are within the same WGS cluster strongly indicating a common source.
Two isolates had phenotypically lost a trait, i.e. they had turned monophasic when isolated from urine samples. However, the same patients had fecal samples that were phenotypically classical Kentucky isolates.