On Friday 26 July 2024, Western Public Health Unit (WPHU) received six legionellosis notifications – more than our monthly average – in one afternoon. The team allocated notifications for immediate interview and regrouped an hour later with preliminary interview outcomes. By 6pm we had confirmation of four Legionella pneumophila serogroup 1 (LP1) cases in adult males living in Melbourne’s Western suburbs all admitted to hospital with respiratory illnesses with onset within days of one another and no clear overlap of exposures.

WPHU informed the Department of Health and Local Public Health Unit (LPHU) Network and asked that LPHUs be on high alert for LP1 notifications over the weekend, consider immediate interview of cases, and contact WPHU to compare exposure sites.

More notifications arrived from 6am Saturday. By early afternoon 13 LP1 notifications had been received across four LPHUs with no common exposure, and an urgent assessment meeting was convened with the Department of Health and other affected LPHUs. Cases had symptom onset from mid-July and had dispersed exposures to the southeast of an industrial area in Melbourne’s northwest. Outlying cases with residence and most exposures outside of the general dispersion pattern were used to identify a potential signal in the industrial area.

By Monday morning 17 cases had been reported. An environmental event leading to widespread dispersal of Legionella from the industrial area was considered amongst other hypotheses. Victoria’s cooling tower registration system allowed towers with overlapping close case exposures including within this industrial complex to be rapidly identified and earmarked for testing and treatment whilst the outbreak investigation continued.

The cooling tower responsible for the outbreak was subsequently found to be one of those tested and treated at the beginning of the response.

Background: Seasonal influenza vaccine (SIV) is the most effective tool to prevent influenza infection and associated hospitalisations and deaths. Despite this, coverage remains sub-optimal, especially in school-aged children. We investigate SIV uptake among school-aged Australian children in 2023, compare the uptake between public and private school students, and assess the role of socio-economic inequality in influencing SIV uptake inequity.

Method: We analysed the whole-of-population Person-Level Integrated Data Asset (PLIDA). Vaccination records were extracted from the Australian Immunisation Register, and school type was identified from linked Census 2021. The Oaxaca-Blinder decomposition was used to identify factors driving inequity in SIV uptake between public and private school students.

Results: In 2023, Australia’s population was 27.4 million. Of 9.5 million SIV doses administered, only 0.7 million (7%) went to school-aged children (5-<18 years), despite them comprising 16% of the population. SIV coverage among school-aged children was low (<15% for secondary, and <18% for primary), well below overall population coverage (33%).
Private school students have notably higher SIV uptake than public school peers, with a wider gap at higher education level (coverage is 19.6% in private secondary schools vs. 14.2% in public schools). Private school students, on average, demonstrate greater socio-economic advantage. Differences in observed child, parental, family, and residential-area characteristics explain >60% of total SIV uptake gap among children in the two school types. Of note, parental education, parental income, and socio-economic characteristics of residential area play the most important role.

Implications: SIV uptake among school-aged Australian children is low and unevenly distributed. Addressing socio-economic inequality could reduce vaccination inequity. Further research into the impact of state/national funded SIV policies and alternative methods of SIV delivery for school-aged children, such as live attenuated SIV in a nasal spray and a school-based SIV program, on improving uptake and reducing this inequity could be explored.

The NSW Public Health Rapid, Emergency, Disease and Syndromic Surveillance (PHREDSS) system uses emergency department (ED) data to detect unusual patterns of activity and severity of presentations in near real-time. Presentations are grouped into ‘surveillance syndromes’ by clinician-assigned diagnoses and compared statistically with historical trends. In late 2023, 'pneumonia' presentations rose, exceeding previous peaks throughout 2024. We aimed to characterise this surge, identify surveillance gaps and inform public health strategies.

We analysed PHREDSS data for 'pneumonia' ED presentations from 2015-2024, by demographic and acuity measures (ambulance arrival, triage category and admission). Presentation rates and age-group proportions in 2024 were compared with pre-pandemic averages (2015-2019). Public notification and laboratory data were reviewed for trends in causative organisms. Additional investigations of linked admitted patient diagnoses were conducted.

Compared to the 2015-2019 average (n=26,921), pneumonia presentations were over 1.5 times higher in 2024 (n=49,273). Presentation rates per 100,000 population increased most in children aged 5-16 years (RR 4.46, 95% CI 4.33-4.60) and younger adults aged 17-34 years (RR 2.61, 95% CI 2.53-2.70). Children aged 5-16 years represented 16.3% of pneumonia presentations in 2024 compared to 6.3% in 2015-2019. Although admissions rose, apparent acuity dropped, with a lower proportion of presentations admitted to hospital in 2024. Public laboratory data showed increases in various pathogens, including respiratory viruses and Mycoplasma pneumoniae, however these did not directly reflect pneumonia diagnoses so cannot confirm underlying causes. Linked data results will be presented at the conference.

Despite inherent challenges in pneumonia surveillance, the PHREDSS system rapidly detects changing demographic and severity trends facilitating timely health service planning. Precipitating factors remain undefined, limiting the specificity of public health intelligence. Linked admitted patient data characterises causative organisms but is delayed. Complementing rapid syndromic surveillance with admitted patient and pathology data could promote more tailored public health action.

Background: Egg-adaptive mutations occurring during egg-based influenza vaccine manufacturing can alter the antigenicity of the vaccine virus and reduce recipients’ immune response to circulating viruses, contributing to reduced vaccine effectiveness. We previously demonstrated improved effectiveness of cell-based (QIVc) versus egg-based (QIVe) quadrivalent influenza vaccines against test-confirmed influenza in populations aged 4 to 64 years during the 2017-18 to 2019-20 influenza seasons and aged 6 months to 64 years during the 2022-23 season in the United States. With increasing uptake of QIVc in the paediatric population, the 2023-24 season offered the opportunity to estimate the relative vaccine effectiveness (rVE) of QIVc versus QIVe for preventing test-confirmed influenza specifically in paediatric and adult subpopulations.
Methods: We used linked data from multiple sources, combining electronic health records, medical and pharmacy claims, and laboratory tests in the United States. A retrospective test-negative design was applied among individuals aged 6 months to 64 years vaccinated with either QIVc or QIVe in 2023-24, who had an influenza test obtained within 7 days of an acute respiratory or febrile illness. rVE was estimated using a doubly robust analysis with inverse probability of treatment weighting and multivariable logistic regression. Analyses were performed in the full population and stratified by age: 6 months to 17 years (paediatric) and 18 to 64 years (adult).
Results: The final dataset included 106,779 vaccinated and influenza-tested patients, of whom 57% were classified as paediatric and 43% as adult. QIVc was significantly more effective than QIVe in preventing test-confirmed influenza with estimated rVEs of 19.0% (95% CI: 14.9 – 23.0%) in the full population, 14.7% (8.7 – 20.3%) in paediatric and 18.1% (11.7 – 24.0%) in adult subpopulations.
Conclusions: This study demonstrates improved effectiveness of QIVc compared to QIVe in preventing test-confirmed influenza in both paediatric and adult populations during the 2023-24 season.

Background
Indigenous status data in hepatitis C (HCV) and other communicable diseases notifications can guide strategies to address health inequalities, inform self-determined models of care in HCV and address the disproportionate disease burden including HCV among Indigenous people. HCV notifications are primarily provided to health departments by pathology providers, with Indigenous status collection determined by legislative requirements. This data improves the understanding of HCV trends and burden across priority populations and developing targeted initiatives and policies. We conducted reviews to assess Australian notifications systems capacity to provide surveillance data to track progress to HCV elimination among Indigenous Australians.

Methods
Between 1 April and 30 August 2024, we reviewed public health legislation across Australian jurisdictions to assess the requirements for including Indigenous status in HCV notifications submitted by pathology providers. Additionally, an audit of pathology request forms from NATA-accredited pathology providers was conducted to determine the presence of Indigenous status fields.

Results
Five of eight jurisdictions (NT, SA, TAS, VIC, WA) mandate the collection and inclusion of Indigenous status for communicable disease notifications. Of the five jurisdictions, only two had public laboratories with Indigenous status fields on their request form, while no private laboratories did. Only six of forty-two pathology provider request forms reviewed included an Indigenous status field, with just one being a private laboratory.

Conclusion
Despite mandates in multiple jurisdictions, most private laboratories (which notify majority of HCV cases) failed to include Indigenous status fields, resulting in substantial data reporting gaps. This underreporting hinders our ability to track and respond to the HCV epidemic amongst Aboriginal and Torres Strait Islander people. In addition to ensuring clinicians record Indigenous status in patient management systems, Australian health authorities must ensure compliance with legislative requirements for including Indigenous status in disease notifications and ensure Indigenous status fields are on all pathology forms.

Background
Tuberculosis is a global public health concern. Genomic analysis of Mycobacterium tuberculosis (Mtb) has been at a jurisdictional level, and cross-jurisdictional epidemiology of Mtb in Australia remains poorly understood. We present the first national assessment of Mtb drug resistance and genomic clusters using a decade of genomic data from Australian jurisdictions, as a part of the Australian Pathogen Genomics program.

Methods
Our national dataset of Mtb sequences included retrospective (2015-2022) and 2023 snapshot data, aiming to represent Mtb notifications of culture-confirmed disease. Mtb genomic surveillance was established on AusTrakka, allowing Public Health Laboratories to securely contribute Mtb genomes and metadata. Hierarchical (0, 5 and 12 SNPs) single linkage clustering from pairwise SNP distances were used to identify genomic clusters, and the tbtAMR tool was used for drug resistance prediction. Metadata was combined with genomic analysis to identify Mtb clusters of national public health significance.

Results
6,670 Mtb sequences (retrospective=5,915; snapshot=692) representing cases across all states and territories were examined and comprised 55.49% of all notified cases in Australia from 2015-2023. Mtb lineages 1-4 were detected, with Lineage 2 being the most prevalent and drug resistant. At the 5-SNP threshold, 373 genomic clusters were identified, with the number of genomic clusters increasing to 422 when a relaxed threshold of 12 was applied. Of the 373 genomic clusters, 48 were identified as having public health significance. 31 Mtb genomic clusters spanned multiple jurisdictions with many persisting for >5 years and those with >15 sequences all multijurisdictional. Genotypically inferred drug susceptibility revealed low rates of multidrug resistance in Australian Mtb.

Conclusions
This first-of-a-kind study on Australian Mtb highlights the benefits of undertaking coordinated national sequencing in Australia. Real-time cluster and AMR identification can enhance Mtb control and surveillance in Australia and are essential to minimise Mtb transmission events in a low-incidence country.

Introduction
Australia is a low tuberculosis (TB) incidence country, with a World Health Organization (WHO) incidence estimate of 5.6 cases per 100,000 population in 2022. For more than 30 years, Australia, has maintained TB incidence rates of <10/100,000 population, but progress toward TB elimination and ‘zero local TB transmission’ remains challenging. The WHO ‘Towards tuberculosis elimination: an action framework in low-incidence countries’ provides eight priority actions for TB elimination.

Methods
We critically evaluated different elements of the WHO elimination framework in the context of New South Wales (NSW), Australia. We analysed population and migration, notifiable conditions, and programmatic TB data for NSW and critically reflected on challenges and opportunities for TB elimination.

Results
There were 523 TB cases in NSW in 2024 corresponding to a notification rate of 6.3 per 100,000 population. Ninety-one percent of cases were born overseas, with notification rates tied closely to changes in migration patterns from high TB incidence countries. Pre-elimination rates of TB in the Australian-born non-Indigenous population have been maintained, but the rate of TB in Aboriginal and Torres Strait Islander people in NSW has increased. Approximately 5% of cases per year are likely locally acquired. NSW has made progress against the WHO framework actions including contact investigation, TB treatment in migrants, optimising care for drug-resistant TB, and improved surveillance and programme monitoring.

Conclusion
Most WHO key priorities and actions are embedded in NSW Health policy, but TB elimination remains out of reach in NSW mainly due to migration from high-TB incidence settings. Important opportunities include minimising TB disease risk through increased TB preventive treatment (TPT), early detection of TB disease to minimise local transmission, and understanding how best to improve community engagement.