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.