Testing the intrinsic mechanisms driving the dynamics of Ross River Virus across Australia.

The mechanisms driving dynamics of many epidemiologically important mosquito-borne pathogens are complex, involving combinations of vector and host factors (e.g., species composition and life-history traits), and factors associated with transmission and reporting. Understanding which intrinsic mechanisms contribute most to observed disease dynamics is important, yet often poorly understood. Ross River virus (RRV) is Australia's most important mosquito-borne disease, with variable transmission dynamics across geographic regions. We used deterministic ordinary differential equation models to test mechanisms driving RRV dynamics across major epidemic centers in Brisbane, Darwin, Mandurah, Mildura, Gippsland, Renmark, Murray Bridge, and Coorong. We considered models with up to two vector species (Aedes vigilax, Culex annulirostris, Aedes camptorhynchus, Culex globocoxitus), two reservoir hosts (macropods, possums), seasonal transmission effects, and transmission parameters. We fit models against long-term RRV surveillance data (1991-2017) and used Akaike Information Criterion to select important mechanisms. The combination of two vector species, two reservoir hosts, and seasonal transmission effects explained RRV dynamics best across sites. Estimated vector-human transmission rate (average ß = 8.04x10-4per vector per day) was similar despite different dynamics. Models estimate 43% underreporting of RRV infections. Findings enhance understanding of RRV transmission mechanisms, provide disease parameter estimates which can be used to guide future research into public health improvements and offer a basis to evaluate mitigation practices.

Hepatitis B clinical care provision in pregnancy: A whole-of-population linkage study in Victoria, Australia.

BACKGROUND AND AIM: Pregnancy is a key setting for engagement in chronic hepatitis B (CHB) care, due to the implications for transmission to the infant and antenatal diagnosis representing an opportunity for ongoing follow-up. This study aimed to identify the coverage and predictors of clinical care for women with CHB during and after pregnancy in a population-level cohort. METHODS: Notified CHB cases in Victoria, Australia, were linked with hospitalizations, medical services, and prescribing data, covering the period 1991-2018. Women with an admission for a live birth were identified and services provided during pregnancy were assessed, including general practitioner (GP) or specialist visits, viral load and serology testing, and antiviral treatment. Viral load and serology testing coverage ware also assessed for the 2-year period following pregnancy. Demographic and clinical predictors of viral load testing during pregnancy were assessed. RESULTS: A total of 11 015 birth events occurred for 6090 women with CHB. During pregnancy most had a GP consultation (91.6%); however, only 39.5% had viral load testing and 41.4% had a gastroenterology or infectious diseases specialist consultation. Viral load testing and serology testing in the 2 years after pregnancy occurred in approximately half (47.9% and 52.2%, respectively) with increases over time. Viral load testing was more likely in those born overseas, those with more than one previous birth, and those living in Melbourne. CONCLUSIONS: Despite improvements over time, key gaps were identified in the provision of CHB clinical care during and after pregnancy, with implications for ongoing transmission and adverse outcomes.

The cascade of care for hepatitis C in Victoria, Australia: a data linkage cohort study.

BACKGROUND: Highly effective hepatitis C therapies are available in Australia. However, people living with hepatitis C face various barriers to accessing care and treatment. AIMS: To identify gaps in the cascade of care for hepatitis C and generate estimates of the number living with untreated infection according to population group, using a representative longitudinal study population. METHODS: We linked hepatitis C notification data from Victoria to national pathology, prescribing and death registry data. We assessed receipt of key clinical services in a large cohort who tested positive for hepatitis C from 1 January 2000 to 31 December 2016, with follow-up to 30 June 2018. We estimated the number still living with hepatitis C, adjusting for spontaneous clearance and mortality. RESULTS: The cohort comprised 45 391 people positive for hepatitis C. Of these, 13 346 (29%) received treatment and an estimated 28% (95% confidence interval (CI): 26-30%) were still living with chronic infection at 30 June 2018, with the remainder still living following spontaneous clearance (30%, 95% CI: 29-32%) or having died (12%, 95% CI: 12-12%). Half (50%) of those still living with hepatitis C were born from 1965 to 1980, and 74% first tested positive before 2011. CONCLUSIONS: Despite an enabling policy environment and subsidised therapy, many people in this cohort were not treated. Increased measures may be needed to engage people in care, including those who acquired hepatitis C more than 10 years ago.

Differential COVID-19 case ascertainment by age and vaccination status in Victoria, Australia: a serosurveillance and record linkage study.

Objectives: To compare serological evidence of prior severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection with linked coronavirus disease 2019 (COVID-19) case notification data in Victoria, Australia, and to determine in vitro SARS-CoV-2 neutralisation activity based on prior infection and vaccination history. Design, setting, participants: Four cross-sectional serological surveys were conducted between 30 June and 31 October 2022 (a period of Omicron BA.4/BA.5 dominance) using 1,974 residual serum samples obtained from the Victorian Infectious Diseases Reference Laboratory. Serological results were linked to COVID-19 case notification and vaccination data. Surrogate virus neutralisation testing was performed to obtain in vitro inhibition estimates by anti-nucleocapsid serostatus and COVID-19 vaccination history. Main outcome measures: Adjusted anti-SARS-CoV-2 spike and nucleocapsid seropositivity by sex, age and region of residence; adjusted proportion of cases notified by anti-nucleocapsid serostatus, age and number of COVID-19 vaccination doses received; adjusted percentage in vitro inhibition against wildtype and Omicron BA.4/BA.5 SARS-CoV-2 variants by anti-nucleocapsid serostatus and COVID-19 vaccination history. Results: The prevalence of anti-SARS-CoV-2 nucleocapsid antibodies was inversely proportional to age. In October 2022, prevalence was 84% (95% confidence interval [95% CI]: 75-93%) among 18-29-year-olds, compared to 39% (95% CI: 27-52%) among ≥ 80-year-olds. In most age groups, approximately 40% of COVID-19 cases appear to have been notified via existing surveillance mechanisms. Case notification was highest among individuals older than 80 years and people who had received COVID-19 vaccine booster doses. In vitro neutralisation of Omicron BA.4/BA.5 sub-variants was highest for individuals with evidence of both prior infection and booster vaccination. Conclusions: Under-notification of SARS-CoV-2 infections in the Victorian population is not uniform across age and vaccination strata. Seroprevalence data that give insights into case notification behaviour provide additional context for the interpretation of existing COVID-19 surveillance information.