NSW Health continually reviews the methods used to monitor respiratory virus activity in New South Wales. This is due to the changes in testing, notification patterns and levels of respiratory infections, including COVID-19, in the community. These changes affect the usefulness of notifications for monitoring activity and community transmission over time. The Public Health, Rapid, Emergency and Syndromic Surveillance (PHREDSS) data, COVID-19 Wastewater Surveillance Program, COVID-19 Whole Genome Sequencing (WGS) data, NSW Sentinel Laboratory Network results and all-cause mortality are currently of most value for monitoring the activity and impact of COVID-19 and other respiratory infections of importance in the community.
Information related to notifications of COVID-19, influenza and respiratory syncytial virus (RSV) are collected in the NSW Notifiable Conditions Information Management System (NCIMS) and stored for analysis in Notifiable Conditions Records for Epidemiology and Surveillance (NCRES). These data assets are managed by Health Protection NSW. Notification data reported in the weekly report are sourced from NCRES. Data is updated as additional information becomes available, therefore data cannot be compared to previous published reports. Notifications are included if they are for a resident of NSW and meet national guidelines for case definitions. Notification rates per 100,000 population by age and Local Health District are calculated using the NSW Department of Planning and Environment population projections.
Significant changes to COVID-19 notification in NSW since 2023:
If a person dies in NSW, their death must be registered under the Births, Deaths and Marriages Registration Act 1995 (Part 7). NSW Health receives a secure feed from the NSW Registry of Births, Deaths and Marriages (BDM) on a daily basis under the Public Health Act 2010 (Part 129A). Deaths reported to a coroner will be registered with the BDM, however cause of death information may be delayed as it is not recorded until there is a coronial determination.
A comprehensive way to estimate the total impact of the COVID-19, and other prolonged and significant health threats, on deaths is to measure changes in the overall number of deaths in a community (regardless of cause), using an indicator called all-cause mortality.
This analysis includes all deaths registered in NSW, including overseas and interstate visitors, sourced from the BDM. We report mortality up to 4 weeks prior to the date of analysis. Not all deaths are registered in this time (in 2023, 95% of deaths were registered within 6 weeks), therefore death rates are corrected to reflect delays in the most recent weeks. A time series of weekly counts of deaths from January 2017 to 2024 year-to-date are presented. The date of death is used to count deaths in a week ending Sunday. Mortality rates are calculated using NSW Department of Planning and Environment population projections. The seasonal baseline is estimated by modelling all-cause mortality rates using seasonally adjusted robust regression. In 2024, deaths from 2017-2023 (excluding 2020 and 2022) are used to fit the model and forecast the seasonal baseline for 2024. The usual variation limits are estimated as 1.96 standard errors above and below the seasonal baseline (95% confidence interval).
This analysis is undertaken as part the surveillance of all-cause mortality in NSW, which informs us about mortality in the presence of ongoing transmission of SARS-CoV-2 and other respiratory virus such as influenza and RSV. This is not the same approach as that used by the Australian Bureau of Statistics or by the Actuaries Institute to examine excess mortality associated with COVID-19 during the pandemic period.
The NSW Wastewater Surveillance Program tests untreated wastewater to detect fragments of the SARS-CoV-2, the virus that causes COVID-19. Gene copy numbers (the number of fragments) are influenced by many factors including virus shedding by people (which varies individually and over the course of the infection), dilution of virus within wastewater (greater dilution during periods of heavy rainfall), the time at which the wastewater sample is collected, and the presence of chemicals and microorganisms in the wastewater that affect how well the testing can detect SARS-CoV-2 virus fragments. Gene concentrations are normalised to 1,000 people per catchment and adjusted for sewer discharge flows. Time-series of these normalised gene concentrations are averaged by week (ending Saturday) then smoothed with exponential moving averages with a backward window length of four weeks. These time series are presented for the three Sydney metropolitan sites (Bondi, Liverpool and Quakers Hill) and a Newcastle site (Hunter - Burwood Beach). Trends in this data should be interpreted over an extended period and fluctuations considered in the context of environmental conditions.
The NSW Public Health Rapid, Emergency, Disease and Syndromic Surveillance (PHREDSS) system provides daily monitoring of most unplanned presentations to NSW public hospital emergency departments (EDs) and all emergency Triple Zero (000) calls to NSW Ambulance. Emergency hospital presentations and ambulance calls are grouped into related acute illness and injury categories. The number of presentations and calls in each category is monitored over time to quickly identify unusual patterns of illness. Unusual patterns could signify an emerging outbreak of disease or issue of public health importance in the population. PHREDSS is also useful for monitoring the impact of seasonal and known disease outbreaks, such as seasonal influenza or gastroenteritis, on the NSW population. The 88 NSW public hospital EDs used in PHREDSS surveillance account for 95% of all ED activity in NSW public hospitals in 2020-2021, including most major metropolitan public hospitals (99%) and rural public hospitals (89%).
PHREDSS ED diagnosis-based surveillance syndromes include clinician applied provisional diagnoses (ICD9, ICD-10AM or SNOMED-CT codes):
The PHREDDS graphs included in the report shoe the number of ED presentations for the specific syndrome and the number of admissions following those presentations.
Whole Genome Sequencing (WGS) is a laboratory procedure that identifies the genetic profile of an organism. WGS can help understand how a virus transmits, responds to vaccination, and the severity of disease it may cause. It can also help to monitor the spread of the virus by identifying specimens that are genomically similar. WGS has been used in NSW since the start of the COVID-19 pandemic to inform epidemiological investigations, and to monitor for and analyse the behaviour of new SARS-CoV-2 variants circulating in the community. WGS is conducted at three NSW reference laboratories and may not reflect the distribution of genome sequences in all cases across NSW. NSW continues to monitor results from cases who are admitted to ICU to track any changes associated with disease severity.
FluTracking is an online health surveillance system that collects data from community volunteers and is used to detect epidemics of influenza across Australia and New Zealand. Participants complete an online survey each week to provide community level influenza-like illness surveillance, consistent surveillance of influenza activity across all jurisdictions over time, and year to year comparisons of the timing, attack rates and seriousness of influenza in the community. Participants are given the option of not continuing to report over the summer season. More information about FluTracking and ways to be involved are available via the FluTracking website.
The NSW Sentinel Laboratory Network comprises 12 laboratories (public and private) throughout NSW who provide additional data on positive and negative test results for common respiratory viruses. These viruses include COVID-19 (4 laboratories only), influenza, RSV, parainfluenza, adenovirus, rhinovirus, human metapneumovirus and enterovirus. This data enables the determination of test positivity, that is, among the people who have been tested, how many test positive. A high positivity suggests high transmission in the community. The number of laboratories that report varies from week to week; and updated data may not be published if the number of reports is insufficient for meaningful interpretation.
