Background and Aim
In 2025, the Pacific experienced its worst dengue outbreak in a decade, with nine Pacific island countries and territories declaring dengue outbreaks. By the end of 2025, over 20,700 confirmed cases and 21 dengue-related deaths were reported, with most dengue-related deaths in children under 18 years. The aim of this presentation is to outline the Australian Government's approach to supporting Pacific island countries during the 2025 dengue outbreak and identify key lessons learned.

Methods and Analysis
Following formal requests for assistance, Australia supported Pacific government-led responses to dengue outbreaks in Kiribati, Nauru, Samoa and Tuvalu. This included the deployment of clinicians; technical advice; provision of essential medical, laboratory, and vector control supplies; diagnostic tools; and risk communication and community engagement. The response was monitored through internal and cross-sectoral outbreak coordination meetings and assessed through an After-Action Review.

Outcomes
Australia was able to provide timely and well-targeted assistance to country-led dengue outbreak responses through established regional health coordination mechanisms – the Pacific Joint Incident Management Team (which includes WHO, the Pacific Community, UNICEF, Australia and New Zealand) and long-standing ties with Australian organisations, which enabled effective collaboration. Existing trust among partners facilitated regular communication, information sharing, and efficient joint mobilisation of resources.

Conclusion and Future Actions
This outbreak offered insights into opportunities to maximise efficiency in a context of complex health priorities and shrinking global public health resources. Noting the high likelihood of future multi-country disease outbreaks in the region, lessons learned and opportunities to further strengthen broad non-disease-specific prevention and preparedness measures will be discussed. Access to vector control tools and entomological capacity; strengthening surveillance and reporting pathways; and enhancing Pacific-regional mechanisms to surge clinical workforce emerged as key areas for consideration, with relevance to broader health security beyond arbovirus outbreaks.

Background and Aim
In early 2025, clinicians alerted ACT Health to a small number of symptomatic acute hepatitis C virus (HCV) infections in males detained at the adult prison in the Australian Capital Territory. This investigation aimed to determine whether an outbreak was occurring, to characterise outbreak epidemiology to inform control measures, and to assess the utility of surveillance tools for this setting.
Methods and Analysis
All HCV RNA positive specimens collected between 1 January 2024 and 31 January 2026 from males detained at the prison were reviewed. An outbreak case was defined as a male with a positive HCV RNA result collected during detention between 3 February 2025 and 31 January 2026. Enhanced clinical and risk factor data were obtained from clinicians via an online notification portal. Dates of detention and prior negative results were used to classify cases by likely place of acquisition. Monthly detections, test positivity, genotype distributions, and maximum plausible viraemic periods in detention were calculated.
Outcomes
A total of 51 outbreak cases were identified, a >7 fold increase compared with the preceding year. Test positivity suggested a true increase in viraemia prevalence rather than improved ascertainment. A sharp peak in detections in April 2025 (n=16) did not necessarily reflect time of transmission. Sixty one percent of cases (30/51) likely acquired their infection during their latest detention, and Aboriginal men were disproportionately affected. Sharing of unsterile injecting equipment in detention was commonly reported. Genotype 3a predominated.
Conclusion and Future Actions
The investigation confirmed an HCV outbreak likely driven by sharing of unsterile injecting equipment within the prison. Use of the notification portal and test positivity data were critical for outbreak confirmation. Enhanced risk factor data not captured in routine surveillance supports the ongoing need for stronger harm minimisation interventions in prison.

Background and Aim
In Victoria, 450–500 tuberculosis (TB) cases are notified annually. Identifying transmission is crucial for detecting secondary cases early, to both reduce the risk of morbidity and transmission. Since 2018, whole genome sequencing (WGS) has been performed on all first Mycobacterium tuberculosis (Mtb) isolates in Victoria. WGS is used to identify and monitor Mtb transmission and potential clusters, and is particularly useful when it identifies previously unknown connections between cases, prompting further epidemiological investigation and creating opportunities for targeted prevention. We describe the use of WGS to identify and investigate a large TB cluster in Melbourne.
Methods and Analysis
In 2022, a new TB cluster was identified when two young men were found to have highly related isolates despite neither having reported knowing each other. The cluster has since grown to 20 highly related isolates in 19 individuals. Individuals in this cluster are predominately young males born overseas who live in or frequently visit Melbourne’s south-eastern suburbs. Many share similar characteristics including mental health issues, homelessness and substance use, and report spending time drinking in parks. The cluster has been associated with a high burden of morbidity and mortality.
Outcomes
WGS has enabled the timely identification of transmission within this population and highlighted the ongoing risk of further spread. Insights provided by WGS, together with information gathered during case interviews have been used by TB Program clinical nurse consultants to inform subsequent contact tracing efforts. Multiagency meetings were convened to generate ideas on ways to improve engagement in affected communities.
Conclusion and Further actions
This cluster demonstrates the important role WGS can play in the identification of TB transmission. To maximise the preventive potential of whole genome sequencing, additional resources are needed to ensure that genomic insights are translated into targeted and effective prevention activities.

Background and Aim:
Whole Genome Sequencing (WGS) has the potential to significantly enhance the surveillance and management of infectious diseases, including tuberculosis (TB). However, evidence on the impact of WGS on real-world decision-making and public health outcomes remains limited. This study aimed to evaluate the utility of WGS in the context of a TB outbreak in Victoria, Australia.

Methods and Analysis:
We conducted a mixed methods study to (1) describe a TB outbreak in Victoria using epidemiological and genomic data and (2) understand the perceived benefits and limitations of WGS through qualitative interviews of laboratory and public health staff.

Outcomes:
From 2017 – 2023, 36 people were linked to a large TB outbreak caused by a lineage 4 cluster with 3 sub-clusters. Epidemiological links identified potential exposure at various churches, a medical centre, family contacts, and travel. Interviews with 10 laboratory and public health staff identified 7 themes: 1) added confidence from high-resolution WGS data; 2) identifying transmission when epidemiological information is limited; 3) informing clinical management; 4) guiding contact tracing and screening; 5) community engagement and interventions; 6) evidence for policy and long-term frameworks; and 7) limitations in interpreting WGS results. In general, WGS was considered a useful tool to guide contact tracing, clinical management, and TB program resource allocation. Practical challenges identified included WGS turnaround times, drawing conclusions from clusters with large single nucleotide polymorphism (SNP) differences (<12 SNPs) compared to sub-clusters (<6 SNPs) and identical isolates (0 SNPs), and uncertainties around public health follow-up actions.

Conclusions and Future actions:
Information derived from WGS data can inform public health decision-making on an individual, program, and policy level. However, challenges identified in this study highlights the need for pathways to support decision-making, such as action-focused WGS training, guidelines to standardise cluster definitions and facilitate follow-up investigations, and improved record-keeping.

Background and Aim
In September 2025, an aged care facility notified the Western Public Health Unit (WPHU) of a gastroenteritis outbreak. Subsequent detection of Yersinia sp. in faecal samples from two residents raised concern for a potential common source. Yersinia sp. is typically found in pork products; symptomatic human infection is rare. WPHU, local council Environmental Health Officers, and the Victorian Government Department of Health, commenced a coordinated epidemiological and environmental investigation to identify the source and implement control measures.

Methods and Analysis
Epidemiological analysis examined menus, food suppliers, symptom onset and exposure timelines to identify common exposures. Inspection focused on food handling, environmental hygiene, kitchen workflow, and targeted food and environmental sampling. Sampling prioritised high-risk foods and preparation areas.

Outcomes
We defined cases as experiencing symptoms of gastroenteritis on or after 8 September and a resident or staff at the facility. We detected 25 cases (22 residents and 3 staff). Faecal samples obtained from seven residents returned two detections of Yersinia sp. and two detections of norovirus. Twenty-four (96%) cases were female. Environmental assessment revealed potential for cross contamination between foods during preparation. Yersinia sp. was identified in a commonly prepared salad item, indicating a likely foodborne transmission pathway potentially involving cross contamination from pork products. Control measures included disposal of implicated products, reinforcement of food safety practices and staff retraining.

Conclusion and Future Actions
This mixed Yersinia and norovirus outbreak highlights the importance of integrated public health and environmental health responses to enteric disease threats in aged care settings.
Future priorities include implementing a joint outbreak response with local council, improving rapid sampling and laboratory escalation for uncommon pathogens, and expanding cross agency training and capability building.
Coordinated, risk based approaches can strengthen outbreak detection and response in complex care environments, particularly where vulnerable populations are disproportionately affected.

Background and Aim
Invasive group A streptococcal infection (iGAS) is caused by Streptococcus pyogenes, a gram positive beta-haemolytic bacterium associated with impetigo, scarlet fever and pharyngitis. iGAS may be associated with bacteraemia, toxic shock syndrome, or necrotising fasciitis. Residential Aged Care Home (RACH) residents are at particular risk due to frail skin, co-morbidities, and close contact living which may facilitate transmission. In December 2025, the Gosford Public Health Unit (PHU) responded to a cluster of invasive Group A Streptococcus (iGAS) cases in a Central Coast RACH. We describe lessons and challenges from this experience.
Methods and Analysis
A Public Health investigation was initiated in November 2025 upon notification of two epi-linked iGAS cases in a RACH. Outbreak measures for a possible cluster were initiated, pending confirmation through whole genome sequencing (WGS). Outbreak management advice was provided to the RACH, recommending active surveillance for localised or invasive GAS infections, and enhanced infection prevention and control measures.
Outcomes
A third iGAS case was notified on 22 December 2025 whilst awaiting confirmatory WGS for the first two cases. Enhanced case-finding identified an additional resident with a localised GAS wound infection. All isolates were highly genomically related and belonged to Sequence Type (ST)178, corresponding to the relatively uncommon M-type emm44.0.
The PHU, in collaboration with the RACH, Urgent Care Service, and a local pharmacy, initiated chemoprophylaxis for 44 residents and 66 RACH staff. There were no further cases to date.
Conclusion and Future Actions
This iGAS cluster highlights the vulnerability of aged care environments. Strong partnerships and utilisation of existing services played a key role in efficient outbreak management. We recommend strengthening outbreak control preparedness in RACHs, staff and family education to increase early detection of infection and reviewing the public health rationale for delaying chemoprophylaxis until institutional iGAS clusters are laboratory-confirmed.

Background and aim
Malnutrition is a major public health issue in Timor-Leste. Enteric bacterial infections, particularly Salmonella may contribute to poor nutritional outcomes through diarrheal disease. Data on the prevalence and molecular epidemiology of Salmonella in Timor-Leste remain limited. This study aimed to identify and characterise circulating Salmonella species in children, animals, and environmental sources.
Methods and analysis
80 children with severe acute malnutrition (SAM) from the national hospital and 156 community-matched controls were enrolled in a case control study. Children’s faeces, animal swabs, and environmental samples from participants homes were collected and tested by microbiological culture, MALDI-ToF and multiplex RT-PCR and phenotypic methods for species identification and antimicrobial susceptibility testing (AST).
Outcomes
From 236 samples from children, eleven (5%) were positive for Salmonella including 4 from hospital cases (2%) and 7 from community controls (3%); 2 samples were detected from water and animal swabs. Preliminary analysis identified two isolates as S. Typhi, while the remaining isolates were non-typhoidal Salmonella spp. No resistance was detected among the tested isolates according to the 2025 EUCAST guidelines.
Conclusion and future actions
We are the first to describe the characteristics of Salmonella in Timor-Leste across humans, animals, and the environment. Strengthening diagnostic capacity would enable more precise identification and improved surveillance of circulating Salmonella serovars in the future. Whole genome sequencing of these isolates is planned to explore genetic diversity, antimicrobial resistance determinants, and potential transmission pathways.

Background and Aim
Salmonella is a leading cause of foodborne gastroenteritis, with young children particularly vulnerable to infection and secondary transmission. In May 2025, an outbreak of salmonellosis was identified at an early education facility in north-eastern metropolitan Melbourne. The incident was first detected following reports of diarrhoea in children, with laboratory confirmation of Salmonella Virchow from faecal samples. A Mother’s Day afternoon tea was identified as a potential point source exposure event. The aim of the investigation was to determine the source and extent of the outbreak, implement control measures, and prevent further transmission, while coordinating with local government and the facility.

Methods and Analysis
A comprehensive investigation was conducted, including case finding, symptom and exposure surveys, and a retrospective cohort analysis. Local council environmental health officers performed site assessments and supervised cleaning. A cross-sectional survey was sent out to parents and staff to identify associations between food consumed at the Mother’s Day event and illness. Environmental and food samples were collected and tested for Salmonella species.

Outcomes
Among 120 attendees, 29 cases were identified across 24 households, including 21 children, six parents, and two staff. No single food item was implicated, however consumption of any food at the Mother’s Day event was associated with increased risk. Cross-contamination in the kitchen was considered the likely contributor, with secondary transmission likely to be person-to-person, especially with illness onset up to 13 days after the event for some individuals. All food and environmental samples were negative for Salmonella Virchow.

Conclusion and Future actions
This outbreak highlighted the vulnerability of early childhood settings to foodborne and secondary transmission events, particularly during communal celebrations involving shared food prepared. Strong coordination is required between facilities, local government and LPHUs.

Background and aim
From January to June 2025, WA experienced the largest cryptosporidiosis outbreak on record. In response, the WA Department of Health (DoH) investigated notified cases to identify risks factors for illness and detect possible point source outbreaks. This enabled a targeted public health response through public communications, and follow up of aquatic centres (AC) and childcare centres (CC).
Methods and analysis
Cryptosporidiosis notifications were reported to the DoH by clinicians and laboratories under the Public Health Act, 2016. Cases were sent an SMS survey or interviewed by telephone about travel, visits to AC and CC during their incubation period. Data were analysed descriptively. Cases were diagnosed by Cryptosporidium species PCR, with a subset of case specimens genotyped using the GP60 typing method.
Outcomes
There were 1082 cryptosporidiosis notifications, with 33% of cases <5 years of age and most (86%) cases lived in metropolitan Perth. Surveys were sent to 836 (77%) cases, with 711 (85%) responding. Of the respondents, 7% had travelled interstate or overseas during their incubation period. Of the locally acquired cases, 48% attended an AC, 52% attended a CC, 17% visited both a AC and a CC and 31% reported attending neither an AC or CC. There were 186 cases linked to 14 probable AC outbreaks. There were two probable CC outbreaks. Of the 76 specimens typed, 75 were C. hominis and the most common subtype (n=70) was IeAIIG3T3.
Conclusion
In 2025, WA experienced a large cryptosporidiosis outbreak, with the emergence of a previously rare C. hominis subtype (IeAIIG3T3) in WA. Surveys conducted by SMS were considered an effective means of case follow up. Fourteen AC outbreaks were identified, highlighting the transmission potential at these centres. A high proportion of cases in young children could also contribute to transmission in other settings, especially households.

Background and Aim

On 17 December 2025, Western Public Health Unit was notified of an outbreak of gastroenteritis was among staff following a Christmas luncheon held at a large metropolitan hospital prepared by an onsite registered food premises. WPHU led an investigation to rapidly identify the source, implement control measures and inform future prevention strategies for similar workplace events.

Methods and Analysis

Using a retrospective cohort study, we distributed an online questionnaire to all hospital and catering staff to understand attendance at the hospital, demographics, symptoms, onset times, and various exposures including food and beverage consumption and location. We defined outbreak cases as attending the hospital during the week of the lunch and experiencing gastroenteritis symptoms, and calculated attack rates, risk ratios, and risk differences for key exposures. Local council Environmental Health Officers inspected the food premises to review hygiene and food handling. Environmental and faecal samples were tested to identify the causative organism.

Outcomes

We identified 141 cases (attack rate of 17%). Ninety-one percent of cases consumed the staff lunch on 16 December. Symptom onset ranged from 15–20 December, peaking on 17 December, with a median incubation period of 32 hours. Ward-based lunch delivery was associated with increased risk of illness (RR 2.47; 95% CI 1.72–3.56). Norovirus GII was detected in all five faecal specimens tested. No environmental or food samples returned positive results. Food safety practices were found to be satisfactory.

Conclusion and Future Actions

This large norovirus outbreak affected hospital operations and led to significant staff absence. One or more infectious persons involved in food handling or packing, not necessarily from the cafeteria staff, are likely to have introduced virus. This demonstrates the value of hand hygiene enforcement, minimising food handlers, exclusion of recently unwell staff, and high food safety standards for large staff events.

Background and Aim
Large indoor gatherings with shared facilities have potential for rapid person to person transmission of infectious diseases. Public health measures, such as mandatory planning to mitigate the risk of disease transmission required during the COVID-19 pandemic, have the potential to prevent large outbreaks of infectious diseases. This study describes an unusually large outbreak of norovirus associated with a national event held in the ACT where public health and infection control measures may have reduced the risk of transmission.

Methods and Analysis
We used telephone interview and an online, self-complete questionnaire to collect data on symptoms, exposures and activities among attendees. An unmatched case control study was used to determine associations between exposures and illness.

Outcomes
An estimated 2000 people attended the event, and 315 cases were identified. Findings were consistent with person-to-person spread of norovirus. Several factors that likely contributed to a perfect storm of disease transmission were identified: unwell attendees—including those with symptoms at the event—were not excluded; there was extensive contact with high-touch surfaces that were not cleaned; and contaminated toilet facilities were inadequately cleaned or were overwhelmed by the volume of illness. Measures that mitigate transmission risk associated with these factors were not explicitly considered by event organisers.

Conclusion and future actions
Basic infection control actions such as exclusion of unwell people, and cleaning of surfaces and high-risk spaces could have significantly reduced the potential for transmission in this outbreak. The outbreak serves as a reminder that public health considerations, such as infectious disease risk assessment and mitigation plans should be considered by organisers of large gatherings. Event guidance should consider including recommendations for how to reduce the risk of infectious disease transmission.