20 September 2021

This report details the methods used for calculating the estimated weekly incidence of COVID-19-like and influenza-like illness in Aotearoa New Zealand, using data from the FluTracking weekly survey.

FluTracking is a participatory health surveillance system for Australia and New Zealand that uses an online, voluntary survey to detect the potential spread of influenza, and more recently COVID-19. Volunteer participants from the general public receive a weekly email prompting them to fill out a survey which asks whether they have experienced any cold, flu, or COVID-19-like symptoms in the previous week.

FluTracking data is an incredibly useful resource for identifying patterns in symptom onset across the New Zealand population. It allows us to report on how symptom onset differs over time and between seasons, as well as across different regions in Aotearoa. However, there are limitations in this data that can reduce the utility of some results.

This report details a methodology that can be used to mitigate some of the limitations in the FluTracking data, and provides case definitions that can be used to inform responses to outbreaks of infectious disease, such as COVID-19. This report also includes a brief summary of FluTracking estimates for May 2020 to April 2021 as an example of applying this new methodology.