Seroprevalence of SARS-CoV-2-specific antibodies in Sydney after the first epidemic wave of 2020.

OBJECTIVES: To estimate SARS-CoV-2-specific antibody seroprevalence after the first epidemic wave of coronavirus disease 2019 (COVID-19) in Sydney. SETTING, PARTICIPANTS: People of any age who had provided blood for testing at selected diagnostic pathology services (general pathology); pregnant women aged 20-39 years who had received routine antenatal screening; and Australian Red Cross Lifeblood plasmapheresis donors aged 20-69 years. DESIGN: Cross-sectional study; testing of de-identified residual blood specimens collected during 20 April - 2 June 2020. MAIN OUTCOME MEASURE: Estimated proportions of people seropositive for anti-SARS-CoV-2-specific IgG, adjusted for test sensitivity and specificity. RESULTS: Thirty-eight of 5339 specimens were IgG-positive (general pathology, 19 of 3231; antenatal screening, 7 of 560; plasmapheresis donors, 12 of 1548); there were no clear patterns by age group, sex, or location of residence. Adjusted estimated seroprevalence among people who had had general pathology blood tests (all ages) was 0.15% (95% credible interval [CrI], 0.04-0.41%), and 0.29% (95% CrI, 0.04-0.75%) for plasmapheresis donors (20-69 years). Among 20-39-year-old people, the age group common to all three collection groups, adjusted estimated seroprevalence was 0.24% (95% CrI, 0.04-0.80%) for the general pathology group, 0.79% (95% CrI, 0.04-1.88%) for the antenatal screening group, and 0.69% (95% CrI, 0.04-1.59%) for plasmapheresis donors. CONCLUSIONS: Estimated SARS-CoV-2 seroprevalence was below 1%, indicating that community transmission was low during the first COVID-19 epidemic wave in Sydney. These findings suggest that early control of the spread of COVID-19 was successful, but efforts to reduce further transmission remain important.

Establishing thresholds and parameters for pandemic influenza severity assessment, Australia.

OBJECTIVE: To implement the World Health Organization's pandemic influenza severity assessment tool in Australia, using multiple sources of data to establish thresholds and measure influenza severity indicators. METHODS: We used data from four reliable sources: sentinel general practitioner surveillance, hospital surveillance, a public health hotline and an influenza-like illness survey system. We measured three influenza severity indicators (transmissibility, impact and disease seriousness) defined using pandemic influenza severity assessment guidelines. We used the moving epidemic method and a seriousness indicator-specific method to set thresholds for indicator parameters using 2012-2016 data. We then applied the thresholds to data from the 2017 influenza season. FINDINGS: We were able to measure and produce thresholds for each severity indicator. At least one laboratory-confirmed influenza parameter was used to measure each indicator. When thresholds were applied to the 2017 season, there was good agreement across all data sources in measuring activity for each indicator. The season was characterized as having high transmissibility and extraordinary impact. Seriousness was characterized as moderate overall and in all age groups except those aged ≥ 65 years for whom it was high. This matched the description of the season produced by the Australian national influenza surveillance committee, based on expert opinion and historical ranges. CONCLUSION: The pandemic influenza severity assessment and moving epidemic method provide a robust and flexible method to enable an evidence-based assessment of seasonal influenza severity across diverse data sources. This is useful for national assessment and will contribute to global monitoring and response to circulating influenza with pandemic potential.

Australian vaccine preventable disease epidemiological review series: tetanus 2003-2019.

Background We examined trends in tetanus notification, hospitalisation and death data from 2003-2019 to assess the impact of adult tetanus booster recommendations in Australia. Methods Tetanus notifications and deaths from the National Notifiable Diseases Surveillance System; hospitalisations from the Australian Institute of Health and Welfare National Hospital Morbidity Database; and deaths from the Australian Coordinating Registry were analysed by age group, sex, Aboriginal and Torres Strait Islander status and state/territory. Annual rates were calculated using Australian Bureau of Statistics mid-year estimated resident populations from 2003-2019 as denominators. To assess the impact of a recommended booster dose of reduced antigen content diphtheria-tetanus-acellular pertussis (dTpa) vaccine for adults aged ≥ 65 years, notification, hospitalisation and death rates of tetanus per 100,000 population were compared pre (2003-2012) and post (2013-2019) the recommendation's introduction. Results There were 63 notifications of tetanus from 2003-2019 with an average annual incidence rate of 0.02/100,000. Similar to previous studies, the burden of tetanus in the Australian population continues to disproportionately affect the elderly, with those aged ≥ 65 years encompassing 63% (40/63) of notifications and 100% (11/11) of the deaths observed in this timeframe. Following the introduction of a recommendation for those aged ≥ 65 years to receive a dTpa booster, average annual notification and hospitalisation rates in those aged ≥ 65 years were significantly lower (notifications: 0.11/100,000 in 2003-2012 and 0.05/100,000 in 2013-2019, p = 0.01; hospitalisations: 0.24/100,000 in 2003-2012 and 0.10/100,000 in 2013-2019, p = 0.01]). The average annual death rate was similar in the two periods (0.002/100,000), although based on small numbers. Conclusions The findings of this analysis suggest a positive impact from the 2013 recommendation. However, the burden is still disproportionately higher in those aged ≥ 65 years and strategies to improve vaccination coverage in older Australians are recommended.

Serological testing of blood donors to characterise the impact of COVID-19 in Melbourne, Australia, 2020.

Rapidly identifying and isolating people with acute SARS-CoV-2 infection has been a core strategy to contain COVID-19 in Australia, but a proportion of infections go undetected. We estimated SARS-CoV-2 specific antibody prevalence (seroprevalence) among blood donors in metropolitan Melbourne following a COVID-19 outbreak in the city between June and September 2020. The aim was to determine the extent of infection spread and whether seroprevalence varied demographically in proportion to reported cases of infection. The design involved stratified sampling of residual specimens from blood donors (aged 20-69 years) in three postcode groups defined by low (<3 cases/1,000 population), medium (3-7 cases/1,000 population) and high (>7 cases/1,000 population) COVID-19 incidence based on case notification data. All specimens were tested using the Wantai SARS-CoV-2 total antibody assay. Seroprevalence was estimated with adjustment for test sensitivity and specificity for the Melbourne metropolitan blood donor and residential populations, using multilevel regression and poststratification. Overall, 4,799 specimens were collected between 23 November and 17 December 2020. Seroprevalence for blood donors was 0.87% (90% credible interval: 0.25-1.49%). The highest estimates, of 1.13% (0.25-2.15%) and 1.11% (0.28-1.95%), respectively, were observed among donors living in the lowest socioeconomic areas (Quintiles 1 and 2) and lowest at 0.69% (0.14-1.39%) among donors living in the highest socioeconomic areas (Quintile 5). When extrapolated to the Melbourne residential population, overall seroprevalence was 0.90% (0.26-1.51%), with estimates by demography groups similar to those for the blood donors. The results suggest a lack of extensive community transmission and good COVID-19 case ascertainment based on routine testing during Victoria's second epidemic wave. Residual blood donor samples provide a practical epidemiological tool for estimating seroprevalence and information on population patterns of infection, against which the effectiveness of ongoing responses to the pandemic can be assessed.

Seroprevalence of Severe Acute Respiratory Syndrome Coronavirus 2-Specific Antibodies in Australia After the First Epidemic Wave in 2020: A National Survey.

BACKGROUND: As of mid-2021, Australia's only nationwide coronavirus disease 2019 (COVID-19) epidemic occurred in the first 6 months of the pandemic. Subsequently, there has been limited transmission in most states and territories. Understanding community spread during the first wave was hampered by initial limitations on testing and surveillance. To characterize the prevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific antibody seroprevalence generated during this time, we undertook Australia's largest national SARS-CoV-2 serosurvey. METHODS: Between June 19 and August 6, 2020, residual specimens were sampled from people undergoing general pathology testing (all ages), women attending antenatal screening (20-39 years), and blood donors (20-69 years) based on the Australian population's age and geographic distributions. Specimens were tested by Wantai total SARS-CoV-2-antibody assay. Seroprevalence estimates adjusted for test performance were produced. The SARS-CoV-2 antibody-positive specimens were characterized with microneutralization assays. RESULTS: Of 11 317 specimens (5132 general pathology; 2972 antenatal; 3213 blood-donors), 71 were positive for SARS-CoV-2-specific antibodies. Seroprevalence estimates were 0.47% (95% credible interval [CrI], 0.04%-0.89%), 0.25% (CrI, 0.03%-0.54%), and 0.23% (CrI, 0.04%-0.54%), respectively. No seropositive specimens had neutralizing antibodies. CONCLUSIONS: Australia's seroprevalence was extremely low (<0.5%) after the only national COVID-19 wave thus far. These data and the subsequent limited community transmission highlight the population's naivety to SARS-CoV-2 and the urgency of increasing vaccine-derived protection.

Evidence for an increase in the intensity of inter-seasonal influenza, Queensland, Australia, 2009-2019.

BACKGROUND: Inter-seasonal influenza cases have been increasing in Australia. Studies of influenza seasonality typically focus on seasonal transmission in temperate regions, leaving our understanding of inter-seasonal epidemiology limited. We aimed to improve understanding of influenza epidemiology during inter-seasonal periods across climate zones, and explored influenza intensity and strain dominance patterns over time. METHODS: Queensland state-wide laboratory-confirmed influenza notifications and public laboratory influenza test data from 2009-2019 were described by demographics, time period, region and strain type. We compared influenza intensity over time using the WHO Average Curve method to provide thresholds for seasonal and inter-seasonal periods. RESULTS: Among the 243 830 influenza notifications and 490 772 laboratory tests reported in Queensland between 2009 and 2019, 15% of notifications and 40% of tests occurred during inter-seasonal periods, with 6.3% of inter-seasonal tests positive. Inter-seasonal notifications and tests substantially increased over time and increases in weekly proportions positive and intensity classifications suggested gradual increases in virus activity. Tropical inter-seasonal activity was higher with periods of marked increase. Influenza A was dominant, although influenza B represented up to 72% and 42% of notifications during some seasonal and inter-seasonal periods, respectively. CONCLUSIONS: Using notification and testing data, we have demonstrated a gradual increase in inter-seasonal influenza over time. Our findings suggest this increase results from an interplay between testing, activity and intensity, and strain circulation. Seasonal intensity and strain circulation appeared to modify subsequent period intensity. Routine year-round surveillance data would provide a better understanding of influenza epidemiology during this infrequently studied inter-seasonal time period.