This study aimed to investigate a four-month Ralstonia pickettii outbreak by characterizing clinical and environmental isolates while also demonstrating the infection control measures taken to identify and eliminate the sources. R. pickettii was isolated from patients’ blood cultures, and an epidemiological investigation was initiated to determine the source of the outbreak. Clonal relatedness among clinical and environmental samples was assessed using pulsed-field gel electrophoresis. In total, R. pickettii was isolated from 14 patient blood cultures and 3 bottles of sterile distilled water. Between April 14 and May 15, six patients had positive port cultures, including four with positive peripheral cultures. The contaminated water was identified as the outbreak source, and its use was discontinued on May 15. Nevertheless, two additional cases occurred in June. Port catheter colonization with R. pickettii was considered to be linked to contaminated water used during chemotherapy preparation. A recall of port catheter patients who received chemotherapy in April–May identified six more cases. Pulsed-field gel electrophoresis revealed two pulsotypes among water isolates, and most clinical isolates were clonally related to clone 1. This investigation highlighted the role of contaminated sterile distilled water and colonized medical devices as potential sources of R. pickettii outbreaks.

In 2024, an outbreak of Salmonella typhimurium affected two regions in Portugal. To identify the vehicle, we conducted a case–case study using a ‘same disease, different time period’ design. We compared S. typhimurium cases linked by whole-genome sequencing (WGS) (cluster cases) with salmonellosis cases notified in 2023 (historical cases) and calculated odds ratios (OR) for food exposures in surveillance data using logistic regression. We performed WGS on 58 isolates from the outbreak period (11/03/2024–2118/06/2024), and all belonged to a single cgMLST cluster (HierCC HC5_410,410). Compared with the 552 historical cases, cluster cases more frequently reported fresh cheese consumption (OR 18; 95% CI: 8.5–38). We visited the implicated cheese production site, identified food safety non-conformities, and enforced hygiene measures. Environmental and product specimens collected at the visit tested negative for Salmonella spp. Taken together, the most plausible vehicle in this outbreak was fresh cheese. The case–case design enabled a rapid, low-cost analysis to support targeted investigation using surveillance data. Using WGS cluster cases as the case definition, rather than all S. typhimurium cases during the outbreak period, yielded a higher OR in the case–case study, increasing confidence in the findings. We recommend this combined approach as part of the toolkit for foodborne outbreak investigations in Portugal in similar contexts.

Cholera remains a major public health concern in conflict-affected Tigray, Ethiopia, where disrupted water, sanitation, and hygiene (WaSH) services and displacement have increased transmission risk. This study analysed outbreak dynamics, attack rates (AR), and predictors of cholera to inform interventions aligned with Ethiopia’s Cholera Elimination Plan (2022–2028). A retrospective analysis was conducted on 802 suspected and confirmed cholera cases reported from 25 July to 4 October 2024 across 25 districts in Central and Northwestern Tigray. Data from the Tigray Health Research Institute line list were analysed using descriptive statistics, Chi-square tests, and Generalized Estimating Equation (GEE) models. Attack rates were highest in Asgede (357.25/100000) and Endabaguna (88.12/100000). Significant associations were observed with age, sex, occupation, water source, travel history, vaccination, latrine access, and contact history. GEE analysis showed strong intra-cluster correlation (α = 0.949). Higher odds of cholera were associated with males, adults aged 16–45 years, and use of unsafe water sources, while vaccination and latrine availability reduced risk. Strengthening WaSH services, vaccination coverage, surveillance, and targeted risk communication is essential to reduce cholera transmission in Tigray.

In September 2020, an unexpected increase in Salmonella Muenchen patient isolates and notifications was observed. We investigated the outbreak to identify the vehicle of infection. RKI defined cases as patients with laboratory-confirmed S. Muenchen infections reported between September 2020 and July 2021. Genomes of clinical, food, and animal S. Muenchen isolates were analysed using cgMLST. We conducted interviews and performed a frequency-matched case–control study. We calculated frequencies and adjusted odds ratios (aOR) using logistic regression. We identified 301 cases in eight federal states in Germany. Hypothesis-generating interviews did not provide a conclusive hint of a possible vehicle. S. Muenchen strains were detected in dried coconut pieces, milk powder used for chocolate production, and a wild swan, all with a cgMLST profile indistinguishable from the prominent node comprising 116 patient isolates. Cases included in the case–control study more often consumed dried coconut pieces (22/30) than controls (2/116) (aOR: 176 (95% confidence interval: 32–954)). In this investigation, cgMLST analysis presented identical strains in three different isolate sources. The case–control study supported dried coconut pieces as vehicle of infection demonstrating the importance of interdisciplinary investigations and underscoring the potential impact of unusual vehicles.

We describe a prolonged outbreak of Salmonella enterica serotype Poona (S. Poona) sequence type (ST) 308, which comprised 13 cases occurring intermittently in North West England between 2016 and 2021. Whole genome sequencing (WGS) results indicated potential exposure to a single source but a lack of good quality data from routine surveillance questionnaires initially made it challenging to identify the cause. Continuing identification of cases in young children in a small geographical area prompted further public health actions, including trawling interviews which identified that ten cases attended the same nursery. As part of enhanced case finding in this nursery, childcare staff were asked to submit faecal samples. One asymptomatic staff member was positive for S. Poona and had worked at another nursery, attended at the time by the first S. Poona child case in this outbreak. Further investigations revealed that the case had previously undergone a cholecystectomy. We report an outbreak caused by persistent carriage and shedding of S. Poona in an asymptomatic individual working with vulnerable groups, which necessitated introduction of risk management measures similar to that for Typhoidal Salmonella. We also demonstrate the utility of combining epidemiological and WGS data in the public health response to Salmonella outbreaks.

In low-prevalence settings, the epidemiological yield of screening strategies for controlling vancomycin-resistant enterococci (VRE) outbreaks has not been fully established. We retrospectively analysed a prolonged VRE outbreak at a 536-bed tertiary-care hospital in Japan from 2010 to 2021 to evaluate sequential screening strategies across epidemic phases and to identify risk factors for VRE acquisition. Hospital-wide, admission-based, antimicrobial exposure-based, passive, and haemodialysis-targeted screening strategies were implemented over time. Screening yields were compared longitudinally, and a retrospective case–control study was performed using data from the initial hospital-wide screening phase. Molecular epidemiology was assessed by pulsed-field gel electrophoresis (PFGE). In total, 169 VRE-positive patients were identified, including seven infections and 162 asymptomatic carriers. Hospital-wide screening in the early epidemic phase showed the highest positivity rate (0.91%), whereas targeted strategies consistently yielded lower rates (0.09–0.34%). Haemodialysis, specific oral care practices, and prior exposure to carbapenems, glycopeptides, and piperacillin/tazobactam were independently associated with VRE acquisition. PFGE revealed substantial genetic diversity, suggesting sustained nosocomial transmission with repeated introductions. Early broad-based screening may be epidemiologically efficient in the initial phase of VRE outbreaks in low-prevalence settings, followed by adaptive refinement for long-term control.

Cryptosporidium parvum is a well-established cause of gastrointestinal illness in both humans and animals and often causes outbreaks at animal contact events, despite the availability of a code of practice that provides guidance on the safe management of these events. We describe a large C. parvum outbreak following a lamb-feeding event at a commercial farm in Wales in 2024, alongside findings from a cohort study to identify high-risk exposures. Sixty-seven cases were identified, 57 were laboratory-confirmed C. parvum, with similar genotypes. Environmental investigations found a lack of adherence to established guidance. The cohort study identified 168 individuals with cryptosporidiosis-like illness from 540 exposure questionnaires (distributed via email to 790 lead bookers). Cases were more likely to have had closer contact with lambs (odds ratio (OR) kissed lambs = 2.4, 95% confidence interval (95% CI): 1.2–4.8). A multivariable analysis found cases were more likely to be under 10 years (adjusted OR (aOR) = 4.5, 95% CI: 2.0–10.0) and have had visible faeces on their person (aOR = 3.6, 95% CI: 2.1–6.2). We provide evidence that close contact at lamb-feeding events presents an increased likelihood of illness, suggesting that farms should limit animal contact at these events and that revisions to established codes of practice may be necessary. Enhancing risk awareness among farmers and visitors is needed, particularly regarding children.

Measles (rubeola) caused by measles virus is highly contagious and can be transmitted via respiratory droplets or can spread via sneezing or coughing of an infected person. In January 2025, two cases of measles associated with international travel seen in unvaccinated individuals of Harris County were reported by the Houston Health Department. This disease which was once declared eradicated from United States (US) in the year 2000, unfortunately has affected a total of 607 cases since January 2025, across the US, with highest number of cases recorded in Texas. Majority of the cases are witnessed in the paediatric population, especially the ones who are unvaccinated or have an uncertain vaccination history. Unfortunately, vaccine hesitancy is an important barrier in achieving measles eradication, and it is more imperative than ever to address this issue in a timely manner. There is an urgent need of virus containment measures to be taken by public health authorities to curb its spread, specifically by reinforcing the importance and safety of vaccinations, debunking myths and educating parents that the recommended two doses of vaccination not only serve as a safety net for their child but also for the community as a whole.

In March 2024, the East Midlands Health Protection Team was notified of a case of invasive Group A Streptococcus (iGAS) infection in an elderly care home resident. Twenty-two days later, another case in a resident from the same floor of the care home was notified. In accordance with national guidelines, an outbreak was declared, and a multidisciplinary outbreak control team (OCT) was urgently convened. Screening for GAS throat carriage was undertaken for staff and residents, excluding those receiving end-of-life care. All isolates were strain typed and characterised. Infection prevention and control (IPC) visits were undertaken to provide ongoing support. Screening identified five residents and five staff members positive for GAS. Antibiotic prophylaxis was provided to all staff throughout the setting (n = 74) and all residents on the affected floor (n = 35). Three individuals were positive on repeat screening. All staff and residents screened negative after 4 months and the two clinical cases recovered. Eleven of the 12 GAS isolates were identified as emm 3.93. This outbreak highlighted the importance of rapid screening, possible only through the deployment of a dedicated team, and rescreening post-decolonising treatment, as a means to contain such outbreaks.

Invasive group A Streptococcal (iGAS) outbreaks have been linked to Community Healthcare Services Delivered at Home (CHSDH). There is, however, very limited evidence describing the epidemiology and mortality of iGAS cases associated with CHSDH. We used routine data to describe iGAS cases in adults who had received CHSDH prior to onset and compare characteristics between CHSDH-outbreak and non-outbreak CHSDH cases, in South East England between December 2021 and December 2023. There were 80/898 (8.9%) iGAS case episodes with CHSDH prior to onset; cases were in elderly people (50% aged 85 and over), and had primarily received wound or ulcer care (93.8%), with almost all care delivered by community nurses (98.8%). The 30-day all-cause case fatality was 26.3%. Emm 1.0 was the most common type (17.5%). In this period, 5/11 iGAS outbreaks (45.4%) were CHSDH-associated, and 25 cases with receipt of CHSDH prior to onset (31.3%, Confidence Interval [CI] 21.3–42.6%) were linked to these outbreaks. On univariate analysis, CHSDH-outbreak case episodes were more likely to be associated with emm pattern genotype E (OR 6.1 95% CI 1.8–20.9), and skin or soft tissue infection clinical presentation (OR 3.6, 95% CI 1.1–12.0) than non-outbreak CHSDH cases. There may be an increased risk of propagation of iGAS outbreaks in patients receiving CHSDH, emphasizing the need for rigorous early infection prevention and control, and outbreak surveillance.

In May 2017, whole-genome sequencing (WGS) became the primary subtyping method for Salmonella in Canada. As a result of the increased discriminatory power provided by WGS, 16 multi-jurisdictional outbreaks of Salmonella associated with frozen raw breaded chicken products were identified between 2017 and 2019. The majority (15/16) were associated with S. enteritidis, while the remaining outbreak was associated with S. Heidelberg. The 16 outbreaks included a total of 487 cases with ages ranging from 0 to 98 years (median: 24 years); 79 hospitalizations and two deaths were reported. Over the course of the outbreak investigations, 14 frozen raw breaded chicken products were recalled, and one was voluntarily withdrawn from the market. After previous changes to labelling and the issuance of public communication for these products proved ineffective at reducing illnesses, new industry requirements were issued in 2019, which required the implementation of measures at the manufacturing/processing level to reduce Salmonella to below detectable amounts in frozen raw breaded chicken products. Since implementation, no further outbreaks of Salmonella associated with frozen breaded chicken have been identified in Canada, a testament to the effectiveness of these risk mitigation measures.

Between February and April 2018, Salmonella typhimurium within a unique 5-single nucleotide polymorphism (SNP) address was isolated from 28 cases with links to a small rural area of Northeast England, with five cases prospectively identified by whole genome sequencing (WGS). Infections had a severe clinical picture with ten cases hospitalized (36%), two cases with invasive disease, and two deaths reported. Interviews determined that 24 cases (86%) had been exposed to a local independent butcher’s shop (Butcher A).

A case-control study using controls recruited by systematic digit dialling established that cases were 68 times more likely to have consumed cooked meat from Butcher A (Adjusted OR 68.1; 95% CI: 1.9–2387.6; P = 0.02). Salmonella typhimurium genetically highly related to 28 of the outbreak cases was also isolated from a sample of cooked meat on sale in the premises.

Epidemiological and microbiological investigations suggest this outbreak was likely associated with the consumption of ready-to-eat foods supplied by the implicated butcher. A relatively large number of cases were involved despite the rurality of the food business, with cases resident across the Northeast and Yorkshire identified using WGS, demonstrating the benefit of timely sequencing information to community outbreak investigations.

We aimed to estimate the secondary attack rate of mpox among UK household contacts and determine factors associated with transmission to inform public health management of contacts, during the global outbreak in 2022. Information was collected via NHS and public health services and included age, gender, place of residence, setting, and type of contact. Aggregate information was summarized for the UK. Record level data was combined for England, Wales and Northern Ireland, and multivariable logistic regression was used to determine factors associated with transmission. The secondary attack rate among UK household mpox contacts was 4% (60/1 526). Sexual contact with the index case was associated with a 11-fold increase in adjusted odds of becoming a case in England, Wales, and Northern Ireland (95% CI 5.5–22, p < 0.001). Household contacts outside of London had increased odds compared to London residents (adjusted OR 2.9, 95%CI 1.6–5.4, p < 0.001), while female contacts had reduced odds of becoming a case (aOR: 0.41, 95% CI: 0.15–0.95). We found a low overall secondary attack rate among household mpox contacts with strong evidence of increased transmission risk associated with sexual contact. This evidence will inform the risk assessment of contacts and support prioritization of those with close intimate contact for follow up.

In September 2023, the UK Health Security Agency identified cases of Salmonella Saintpaul distributed across England, Scotland, and Wales, all with very low genetic diversity. Additional cases were identified in Portugal following an alert raised by the United Kingdom. Ninety-eight cases with a similar genetic sequence were identified, 93 in the United Kingdom and 5 in Portugal, of which 46% were aged under 10 years. Cases formed a phylogenetic cluster with a maximum distance of six single nucleotide polymorphisms (SNPs) and average of less than one SNP between isolates. An outbreak investigation was undertaken, including a case–control study. Among the 25 UK cases included in this study, 13 reported blood in stool and 5 were hospitalized. One hundred controls were recruited via a market research panel using frequency matching for age. Multivariable logistic regression analysis of food exposures in cases and controls identified a strong association with cantaloupe consumption (adjusted odds ratio: 14.22; 95% confidence interval: 2.83–71.43; p-value: 0.001). This outbreak, together with other recent national and international incidents, points to an increase in identifications of large outbreaks of Salmonella linked to melon consumption. We recommend detailed questioning and triangulation of information sources to delineate consumption of specific fruit varieties during Salmonella outbreaks.

In the third week of September 2022, an outbreak of measles was reported from a slum in Eastern Mumbai, India. We sought to investigate whether failure to vaccinate or vaccine failure was the cause. We constructed an epidemic curve, drew a spot map, and calculated the attack rate and case-fatality ratio. We calculated vaccine effectiveness (VE) for one and two doses of measles vaccine in an unmatched case–control study and did stratified analysis by sex, availability of vaccination card, and migrant status. We identified 358 cases and four deaths with a 11.3% attack rate and 1.1% case fatality, both being highest among 0–24-month-old boys. The epidemic curve suggested a propagated mode of spread. The VE for two doses was 64% (95% confidence interval (CI): 23–73%) among under-5-year-old children and 70% (95% CI: 28–88%) among 5–15-year-old children. Failure to vaccinate, consequent to the COVID-19 pandemic, and vaccine hesitancy might have led to the accumulation of susceptible children in the community. Additionally, the occurrence of case-patients among vaccinated suggests reduced VE, which needs further investigation into humoral and cell-mediated immunity as well as contributory factors including nutritional status. Outbreak response immunization to complete immunization of missed and dropout children was carried out to control the outbreak.

Enteric bacterial infections are common among people who travel internationally. During 2017–2020, the Centers for Disease Control and Prevention investigated 41 multistate outbreaks of nontyphoidal Salmonella and Shiga toxin-producing Escherichia coli linked to international travel. Resistance to one or more antimicrobial agents was detected in at least 10% of isolates in 16 of 30 (53%) nontyphoidal Salmonella outbreaks and 8 of 11 (73%) Shiga toxin-producing E. coli outbreaks evaluated by the National Antimicrobial Resistance Monitoring System. At least 10% of the isolates in 14 nontyphoidal Salmonella outbreaks conferred resistance to one or more of the clinically significant antimicrobials used in human medicine. This report describes the epidemiology and antimicrobial resistance patterns of these travel-associated multistate outbreaks. Investigating illnesses among returned travellers and collaboration with international partners could result in the implementation of public health interventions to improve hygiene practices and food safety standards and to prevent illness and spread of multidrug-resistant organisms domestically and internationally.

In 2009, a large outbreak of leishmaniasis, associated with environmental changes, was declared near Madrid (Spain), in which Phlebotomus perniciosus was the vector, whereas the main reservoirs were hares and rabbits. Analysis of isolates from humans, vectors and leporids from the focus identified the Leishmania infantum ITS-Lombardi genotype. However, multilocus enzyme electrophoresis (MLEE), the reference technique for Leishmania typing, and sequencing of the hsp70 gene, a commonly used marker, were not performed. In the present study, 19 isolates from P. perniciosus (n = 11), hares (n = 5) and rabbits (n = 3) from the outbreak area, all characterized as ITS-Lombardi in previous studies, were analysed by MLEE and hsp70 sequencing. The hsp70 results confirmed that all the analysed strains are L. infantum. However, by MLEE, 4 different zymodemes of L. infantum were identified based on variable mobilities of the NP1 enzyme: MON-34 (NP1100, n = 11), MON-80 (NP1130, n = 6), MON-24 (NP1140, n = 1) and MON-331 (NP1150, n = 1). The relative frequency of these zymodemes does not correspond to their usual occurrence in Spain. Moreover, MON-34 and MON-80 were found in P. perniciosus, hares and rabbits for the first time. These findings continue to provide insights into the outbreak and call for further studies with a higher number of strains.