Sandra Simon

Between July and October 2024, 216 cases with genetically related Salmonella Blockley sequence type 52 were identified in France (n = 56), Germany (n = 30), the United Kingdom (UK) (n = 129) and the United States (US) (n = 1). Case interviews in the UK identified tomatoes as a possible vehicle of infection. A rapid case–control study with 29 cases and 87 controls was conducted to investigate this hypothesis, using pre-existing control data. Multivariable, Firth penalised logistic regression was used to explore associations between illness, food exposures and retailers. Consumption of tomatoes and shopping at Retailer A (adjusted odds ratio (aOR) = 10.75; 95% confidence interval (CI): 1.52–103.16) was associated with being a case. Salmonella spp. was not detected in any of the 312 tomato samples tested by a standard culture method, but a low concentration of Salmonella DNA was detected in two enriched broths by PCR. These detections could not be confirmed by culture. Evidence derived from epidemiological, microbiological and food chain investigations in the UK identified imported tomatoes from Morocco as the most likely vehicle of infection.

Salmonella enterica subsp. enterica serovar Enteritidis ( S . Enteritidis) is the second most common serovar causing human salmonellosis in Aotearoa New Zealand (NZ). Sequence type (ST)183, which includes phage types 9a and 11, was the second most frequently isolated S . Enteritidis strain from human cases between 2020 and 2023. This ST is considered endemic in NZ as well as in mainland Europe and Great Britain, where the European hedgehog ( Erinaceus europaeus ) is a recognized wildlife reservoir. Hedgehogs were introduced to NZ in the late 19th century; however, their role in the ecology of ST183 in NZ has not been formally evaluated. The aim of this study was to investigate whether hedgehogs act as a reservoir for S . Enteritidis ST183 in NZ and to assess the evolutionary history and epidemiology of this strain across human, animal and environmental contexts. We analysed human, animal and environmental ST183 isolates, including hedgehog carcasses opportunistically sampled in NZ, using Bayesian phylogenetic methods integrated with national epidemiological data. Although S . Enteritidis ST183 was isolated from three of 45 hedgehog carcasses during our study, consistent with recent prior detections of ST183 in NZ hedgehogs, Bayesian phylogenetic analysis supports a most recent common ancestor for currently circulating ST183 strains in the late 20th century, ~100 years after the introduction of hedgehogs into NZ, providing no evidence that the strain was introduced concomitantly with hedgehogs. Epidemiological analysis revealed that, unlike in Europe, ST183 infections in NZ are more common in people aged over 60 years compared with non-ST183 S . Enteritidis infections, with rural residence and contact with farm animals identified as key risk factors. Together, these findings suggest that S . Enteritidis ST183 is established within the NZ rural environment, with evidence of interspecies transmission. While hedgehogs may contribute to the maintenance of ST183, they are unlikely to represent the original source of introduction, indicating a complex, multi-host ecology.

Notifications of Salmonella Strathcona infections increased in Europe in 2023 prompting a multi-country outbreak investigation. We aimed to describe the epidemiology of S . Strathcona infections in 17 European countries 2011–2024, investigate the genetic relatedness of S . Strathcona isolates and identify the vehicle. Cases were persons residing in the study area and with a laboratory-confirmed S . Strathcona infection 2011–2024. Confirmed cases had a S . Strathcona isolate clustering with the outbreak reference strain in core genome multilocus sequence typing (cgMLST) within 7 allelic differences (AD) and possible cases within 8–13 AD. Probable cases had an epidemiological link to a confirmed case and non-outbreak cases had an isolate > 13 AD from the outbreak reference strain. Since 2011, 662 S . Strathcona infections have been identified: 469 confirmed, 161 probable, 13 possible and 19 non-outbreak cases. Median age of the cases was 34 years (IQR: 19–58 years) and 306 (47.5%) were notified in 2023–2024. Most sequenced isolates (469/496; 94.5%) were highly genetically related (≤ 7 AD) over time and across countries, compatible with a common source. Epidemiological and traceback investigations identified small tomatoes from Sicily as the suspect food vehicle. Stringent control measures at the source are needed to stop the contamination and prevent future cases.

A food-borne outbreak with about 200 Salmonella Umbilo cases occurred mainly between July and September 2024 in several European countries. Collaborative work between outbreak teams in Germany, Austria and Denmark, including epidemiological and microbiological investigations, allowed to rapidly identify rocket salad as the likely infection vehicle. Salmonella Umbilo was detected in rocket salad, and later in baby spinach. The food isolates and clinical outbreak strain were genetically closely related. Both food items originated from the same company in Italy.