Eurosurveillance - Volume 30, Issue 41, 16 October 2025

Finland experienced three invasive pneumococcal disease (IPD) outbreaks among shipyard workers at the same shipyard, in 2019, 2023 and 2025. During the latest outbreak (30 April–6 June 2025), 13 cases were reported, with six confirmed. All five isolates from blood culture-positive cases were serotype 4 – sequence type 801. These were nearly indistinguishable from three isolates from the 2019 outbreak, nine Finnish IPD surveillance isolates and isolates of a 2019 Norwegian shipyard outbreak. We found an association with welding.

Oropouche fever is a vector-borne disease endemic in Central and South America. Infection with Oropouche virus (OROV) was confirmed in June and July 2024 in 13 patients travelling from Cuba to Spain. These patients presented fever, headache, myalgia and arthralgia, and three patients exhibited a biphasic course, with two developing transient neurological symptoms. Oropouche virus infection was diagnosed using reverse transcription quantitative PCR (RT-qPCR) and neutralisation tests. Viral RNA was detected in specimens from serum, urine, plasma and whole blood; from four urine samples up to 24 days post-symptom onset. Phylogenetic analysis of one OROV strain (OROV SP2024) isolated from one patient, demonstrated it clustered closely with reassortant strains circulating in Brazil and imported cases in Italy. These findings underscore the importance of including OROV in the differential diagnosis of febrile illnesses in returning travellers and demonstrate the diagnostic value of analysing multiple sample types. Enhanced clinical awareness and diagnostic capacity are essential to improve detection and surveillance of OROV among international travellers from affected regions.

Between 1 November and 12 December 2019, a Legionnaires’ disease (LD) outbreak occurred in the Strasbourg metropolitan area, France. Epidemiological, environmental and genomic investigations (nested sequence-based typing and whole genome sequencing (WGS)) were undertaken to locate the outbreak source, characterise the causal Legionella strain, and understand its spread. Through a positive urinary antigen test, 28 cases (14 male; 14 female) with 70 years median age (range: 42–88 years) were diagnosed. Two died. For nine cases, typing revealed L. pneumophila serogroup 1 (Lp 1) sequence type (ST) 62 infection. Mapping where cases were during their incubation period pointed to a place south-west of Strasbourg city as the outbreak epicentre. There, in the biomass condensing boiler of a heating plant, high Lp 1 contamination levels (10⁵–10⁶ CFU/L) were discovered. Eight environmental Lp 1 isolates from inside the plant were ST62. Analysing WGS data from these isolates and the nine Lp 1 ST62 clinical isolates, found their sequences clustering with zero to two single nt polymorphisms. Sub-optimal maintenance and warm weather before the boiler started operating may have allowed Lp 1 proliferation within, with boiler fumes subsequently disseminating Lp 1, thereby exposing people. This outbreak highlights potential LD risks arising from innovative energy-saving heat production processes designed to reduce greenhouse gas emissions.

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.

Identifying and controlling food-borne disease outbreaks (FBDO) remain important public health objectives. There is plenty of guidance on how to detect potential FBDO, e.g. epidemiologically or microbiologically. Likewise, the conduct of an outbreak investigation has long been codified in steps and adapted for FBDO. However, what is less clear is when to act, mainly when to implement appropriate control measures. This is particularly challenging when the causative agent has not yet been detected in the suspected food vehicle(s). The decision on when to act is complex and depends, besides the available evidence, also on other factors, such as the dynamic of the outbreak or the disease severity. No guidance exists for this decision. Notably, an FBDO investigation provides circumstantial evidence on the culprit, and its careful assessment entails an inherently subjective element. There is a need across sectors and countries in Europe for harmonising the view on what constitutes sufficient evidence for furthering investigations and timely taking action, depending on the outbreak situation. A common understanding and possibly a harmonised legislation are the basis for streamlining discussions and decisions during FBDO, thereby preventing the delay of implementing necessary control measures.