FluTracking: Weekly online community-based surveillance of respiratory illness in Australia, 2020–2022 Report

FluTracking, an online participatory respiratory surveillance system, revealed that the coronavirus disease 2019 (COVID-19) pandemic led to historically low levels of fever and cough (FC) in the 2020–2021 influenza seasons in Australia. In 2022, the influenza peak occurred earlier and was shorter compared to pre-pandemic seasons. Based on weekly percentages of participants reporting FC, FluTracking identified four Omicron waves (BA.1, BA.2, BA.4/BA.5 and a mixed Omicron variant wave). These waves, while consistent with laboratory-confirmed COVID-19 trends, showed higher FC incidences in the BA.4/BA.5 and mixed variant waves. During the Omicron waves in 2022, up to 60% of FluTracking participants with FC reported positive SARS-CoV-2 tests, a significant increase from the less than 10% positivity rate for most of 2020–2021. These trends mirrored the timing of rises in National Notifiable Disease Surveillance System (NNDSS) COVID-19 notifications, although peak magnitudes varied between the two systems. Before November 2021, fewer than half (49.9% weekly mean) of participants with FC, and fewer than a third (27.7% weekly mean) with runny nose and sore throat reported being tested for SARS-CoV-2. Following the introduction of rapid antigen tests (RATs) in November 2021 and the spread of the Omicron variant of SARS-CoV-2 in early 2022, testing rates increased for both symptom profiles in 2022. Additionally, the reopening of international borders and the resurgence of influenza led to expanded respiratory panel testing in drive-through clinics, marked by a 36% increase in the mean weekly percentage of participants reporting an influenza polymerase chain reaction (PCR) test. FluTracking's participation grew by 107% in 2020 compared to 2019, then declined by 17.7% in 2021, likely due to participation and pandemic fatigue. However, participation stabilised with a 0.2% increase in 2022 compared to 2021. FluTracking offers valuable insights into respiratory illness trends, changes in testing behaviours, and positivity rates for influenza and SARS-CoV-2.