More than 300 people were part of a Salmonella outbreak in Czech Republic and Slovakia in 2017 and 2018 that was traced to contaminated powdered egg products.
The probable outbreak cause was used as an ingredient in multiple food types. The source of contamination was a piece of machinery used for drying liquid egg into powder.
Czech Republic and Slovakia report the most salmonellosis cases in Europe but there is a lack of evidence on the sources of foodborne outbreaks, according to a study in Eurosurveillance. In this incident, scientists found gaps in the interviewing strategy that was focused on egg and chicken meat consumption.
In August 2017, the number of Salmonella Bareilly cases reported in the Czech Republic exceeded the annual total of recent years which was up to 25 infections. The outbreak was recognized in the Czech Republic in October that year. In November, the State Veterinary Administration (SVA) was given information about the outbreak to start investigating a probable source of infection.
325 sick over 15 months
The SVA identified a Salmonella Bareilly isolate closely related to human outbreak isolates in a powdered egg product called dried egg melange. This led to the agency investigating the company making the powdered egg and inspections at farms that produced eggs for further processing.
The first confirmed Salmonella Bareilly patient had disease onset in July 2017. The number of infections peaked in October 2017, and the last confirmed patient was reported in October 2018. In total, 250 probable cases were identified in the Czech Republic and 75 in Slovakia. Two small peaks were observed in Slovakia in October 2017 and April 2018.
All age groups were affected in both countries. The highest number of cases was reported in the 1 to 4 years old group. In the Czech Republic, 69 people required hospitalization and in Slovakia 23 needed hospital treatment but no deaths were recorded.
The outbreak touched all 14 Czech regions and all eight Slovak areas, with low numbers of patients in each. The weekly number in each region did not exceed five. This meant the outbreak was seen only at national levels, resulting in late recognition, said researchers.
Finding contamination source
A spray dryer was identified as the source of contamination. Researchers said spray dryers should be considered potential sources for cross-contamination of powdered egg products with Salmonella.
Powdered egg products are considered safe because of thermal treatment and low water activity, but contaminated spray dryers have previously been described as outbreak sources. Products such as egg yolk, egg white, or a mixture of both are ingredients in multiple foods and additional heat inactivation is not required.
In July 2018, the dryer was moved from its previous location to a new one and production of test batches of dried eggs was started. These batches had an unsatisfactory sensory quality, so the company tested products. Salmonella Bareilly was detected in a powdered egg product made in July 2018; contamination of the item was recognized in September but these batches were not sold.
The sprayer had been operating at the first location, where the last batch of dried egg products was produced in March 2017, but this company went out of business in 2017. The spray dryer remained there until July 2018 when it was moved.
The machine underwent repeated cleaning and disinfection. Batch controls were performed from September 2018 until July 2019 and Salmonella Bareilly-positive powdered egg products were repeatedly identified.
At the end of June 2019, contamination of the whole technology of the spray dryer was confirmed. In July, all powdered egg items produced since January 2019 were recalled and the facility was closed with a view to rebuilding the technology.
The trawling questionnaire didn’t provide a clear indication of the contaminated item. However, it did help experts understand that the vehicle was probably widely distributed by grocery chains throughout both countries and was not linked to any unusual or imported foods.
A closely related Salmonella Bareilly isolate was detected in egg melange in September 2018. Trawling questionnaire data were re-evaluated and a possible exposure to items containing powdered egg products was found in all cases.
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