Flutracking: Weekly online community-based surveillance of influenza-like illness in Australia, 2017 Annual Report

Flutracking participation continued to grow, with a total of 33,947 participants in 2017 (a 9.5% increase from 2016). The majority of participants completed their survey within 24 hours of the email being sent (average 72.5% responses received in 24 hours). Overall, the rate of influenza-like illness (ILI) in 2017 was higher and remained elevated for a longer period compared to previous years except for the 2009 pandemic. Flutracking placed the severity and magnitude of the influenza season into historical context. Following the highest number of laboratory-notified influenza cases on record (2.8-fold increase from 2016), Flutracking data demonstrated a large increase in the percent of participants with fever and cough that were tested for influenza (2.9% to 5.0% for 2016 and 2017 respectively) and thus determined it was increased laboratory testing that contributed to the substantial increase in influenza notifications. Flutracking participants with fever and cough that were tested for influenza have increased each year from 2013 to 2017 at the national level, with a large increase from 2016 (2.9%) to 2017 (5.0%). The peak weekly fever and cough attack rate occurred in mid-August, with 4.1% ILI in the unvaccinated, compared to 3.1% in vaccinated Flutrackers. In the peak four weeks of ILI, 12.3% of participants experienced an episode of fever and cough. Divergence between the vaccinated and unvaccinated participants' ILI percentages was highest during the week ending 6 August 2017 (4.1% in the unvaccinated group and 2.7% in the vaccinated group). The timing of the ILI peak amongst Flutracking participants was consistent with peak notifications of laboratory-confirmed influenza.