A total of 14 patients in eight states were identified with illness onsets during March 21 - April 9 and three were hospitalized.
Epidemiological evidence indicated Persian cucumbers as the source of Salmonella Oslo infections but the pathogen was not isolated from any cucumbers.
It is not the first time there has been a delay in reporting an investigation of Salmonella in cucumbers – an outbreak which sickened 275 people in 2014 was made public in 2015.
Rare serotype and new PFGE pattern
The Oslo serotype is rare with about 25 cases reported each year nationally.
The pulsed-field gel electrophoresis (PFGE) pattern was new in the database with no previous infections or outbreaks having been identified.
It is the fourth Salmonella outbreak since 2013 associated with cucumbers, with more than 1,200 illnesses and 260 hospitalizations in the previous three.
Officials in Minnesota and Michigan initiated the investigation when four people with Salmonella Oslo infections were identified.
Interviews of those ill found shopping at an unnamed national chain grocer and purchasing produce was common.
Of thirteen patients interviewed using a supplemental questionnaire about exposures in the week before illness onset, 12 reported eating cucumbers in this period.
Among the 12 patients who ate cucumbers, 11 reported Persian or “mini” cucumbers, which are small, seedless cucumbers with smooth skin.
Eight of 13 respondents reported purchasing cucumbers from the national chain grocer.
The retailer removed all Persian cucumbers from shelves while investigation and traceback efforts were ongoing.
This action in addition to short product shelf life, likely contributed to the small size and short duration of the outbreak, said the researchers.
The investigation identified two Canadian Persian cucumber suppliers but could not find a single grower.
Samples collected from the point of sale, patients’ homes and one of the Canadian suppliers were negative for Salmonella.
Growers who could have supplied the cucumbers were in Canada, Mexico and the Dominican Republic.
The Canadian-grown cucumbers would have also been distributed in Canada and no reported clinical cases matching the US outbreak pattern were identified.
Researchers said the outbreak highlights difficulties associated with investigations in which short shelf life produce items are suspected.
“Given that the typical shelf life of cucumbers is 10–14 days, suspected cucumbers were no longer available in homes at the time ill persons were interviewed,” they said.
“In addition, Salmonella was not isolated from any cucumbers collected from ill persons or grocery stores, although the samples collected from points of sale and distribution might not have originated from the same farm as those consumed by persons before illness onset.”
As prevalence of Salmonella in cucumbers is unknown, FDA has enhanced sampling for domestic and imported whole, fresh, raw cucumbers within fiscal year 2016.
The data (380 domestic cucumber samples and more than 1,200 imported samples) will suggest whether common factors, such as season, region, and whether the product was made domestically or imported, are associated with contamination.
“Outbreak of Salmonella Oslo Infections Linked to Persian Cucumbers - United States, 2016”
Authors: Bottichio L, Medus C, Sorenson A, et al.