EU countries highlight foodborne illness investigations

Researchers from Germany, Belgium, and Spain have presented their work on solving outbreaks and pathogen-specific questions at a European meeting.

The European Scientific Conference on Applied Infectious Disease Epidemiology (ESCAIDE) was organized by the European Centre for Disease Prevention and Control (ECDC).

Since 2020, integrated genomic surveillance (IGS) has been introduced for surveillance of salmonellosis in Germany with routine sequencing of common serovars such as Salmonella Enteritidis and Typhimurium and event-based sequencing of other types.

From 2020 to 2023, scientists detected 186 clusters including 101 of Salmonella Typhimurium and 29 of Salmonella Enteritidis. Clusters increased from 21 in 2020 to 53 in 2023, while the average size decreased from 33 to 12 isolates per cluster. In total, 59 clusters show recurring patterns over more than two years and 32 were confirmed as multinational. For 71 clusters, genetic matches from food, animals or the environment were detected.

“With further establishment of IGS in Germany, we are able to detect more clusters at an earlier stage resulting in higher total numbers and smaller cluster sizes. Matches from food, animals or the environment as well as multi-nationality and recurrence of clusters can help to identify possible vehicles and sources of infection.”

Listeria and STEC
In December 2020, whole genome sequencing detected a cluster of previously unrelated Listeriosis cases. Initial infections were notified in December 2020 and clustered in southern Germany. Of the 20 cases, five were pregnancy related, nine were from Baden-Wuerttemberg and eight from other states. They ranged in age from under 1 to 93, 13 were female and seven male. Two cases died but not due to Listeriosis.

Ten of 13 cases interviewed mentioned eating blackened pickled olives during their incubation periods. In September 2023, CVUA-Stuttgart sequenced a matching voluntary self-monitoring Listeria sample submitted by a manufacturer. The spike of an industrial tin opener for blackened olives was identified as the reservoir. Voluntary self-monitoring and sequencing of all bacterial food samples led to the finding of blackened olives as the outbreak vehicle. Regular sampling and daily disinfection of the tin opener were ordered. After October 2023, no more cases were notified.

In 2023, 4,354 cases of Shiga toxin-producing E. coli (STEC) were notified in Germany, an increase compared to the pre-pandemic years of 2015 to 2019. Similar trends in Denmark and Norway were driven by changes in laboratory diagnostic methods. There were 73 hemolytic uremic syndrome (HUS) cases in 2023 and 2022 in Germany.

Data from the national database of notifiable diseases in 2023 was compared to the median in 2015 to 2019. Notifications increased in all age groups, with the strongest surge in those older than 60. Researchers did not detect major changes in gender distribution, number of imported cases, proportion of hospitalizations or a rise in HUS cases. Ten of 17 labs reported the use of multiplex-PCR and six introduced it in 2023.

The increase in STEC notifications was likely due to more frequent testing by multiplex-PCR rather than a true rise in infections. Findings underscore the importance of monitoring diagnostic practices when evaluating trends in surveillance data, said scientists.

Belgian focus
Culture-independent diagnostic techniques (CIDT) are used to detect gastrointestinal pathogens as they offer short turnaround times and high sensitivities. However, the absence of clinical isolates may hamper epidemiological investigations and public health surveillance. In Belgium, CIDT for gastrointestinal pathogens are not widely used yet but a change in the reimbursement conditions to cover CIDT might affect lab practices.

As part of the project United 4 Surveillance, experts carried out an online survey in April 2024 among 113 medical laboratories and 90 labs participated. For STEC, up to 55 percent of the labs are currently using CIDT with an increase to 85 percent when CIDT will be added to the reimbursement conditions. For Campylobacter, Salmonella, Yersinia, and Shigella, 75 to 95 percent of labs currently perform culture, but a change towards CIDT is foreseen due to the reimbursement rules.

More than 80 percent of labs intend to perform reflex cultures or send samples to the national reference centers. Scientists found a switch in diagnostic practices towards CIDT for gastrointestinal pathogens is expected but there was also a strong intention to participate in surveillance activities.

Also in Belgium, researchers have assessed the association between Yersinia enterocolitica Biotype 1A (BT1A), which is generally regarded as non-pathogenic, and gastrointestinal symptoms.

Among patients, 99 of 183 were female; 60 were over 65 years old and 16 were under the age of 4. In 103 cases, BT1A was reported as the etiological agent of gastrointestinal symptoms; 24 required hospitalization and 18 were immunosuppressed. This demonstrates the ability of BT1A strains to cause gastrointestinal symptoms. Experts said it was crucial to implement a system for routine identification and characterization of this biotype.

Spain and Salmonella Chester
In August 2023, Germany reported two Salmonella Chester clusters linked to travel to Spain in EpiPulse, affecting seven European countries. The Spanish Reference Laboratory for salmonellosis also detected an increase in Salmonella Chester, with the most cases ever recorded in 2023.

Researchers analyzed cases in Spain between January and December 2023 and 45 Salmonella Chester isolates, which included 31 from humans and 14 from food. They identified 179 cases, a five-fold increase from 2022. Patients ranged in age from under 1 to 92 years old and one person died.

Six clusters were identified. Cluster 1 comprised 14 isolates from chicken-derived food, 16 from broilers and 24 human cases from 2021 to 2024. Cluster 2 had isolates from egg yolk, salmon-derived food and 26 from humans. Clusters 1 and 2 were linked to the German cases.

Clusters 3 to 6 had two to four human isolates per cluster. Investigations into the origin of broilers traced 11 of the 17 isolates back to imports, while five originated from broilers in a Spanish incubator. Contaminated salmon, egg yolk, and chicken-derived food were detected in Valencia.

Chicken-based products were a likely source of infection but could not explain all cases. Salmonella Chester is not listed in EU-regulation for Salmonella types of public health significance. Continued detection in humans in 2024 suggests potential introduction, colonization, and persistence, warranting intensified surveillance and stricter control measures, said scientists. 

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Source: https://www.foodsafetynews.com/2024/12/eu-countries-highlight-foodborne-illness-investigations/