Estimating the case detection rate and temporal variation in transmission of COVID-19 in Australia

May 14, 2020


Modelling released by the Australian Government estimating the case detection rate and variation in transmission of COVID-19 in Australia is based on work outlined in this technical report.

This work represents an important shift in the modelling from scenarios to inform preparedness based on international data, to analyses of the Australian epidemic. It informs understanding of how effective the recent actions taken to slow the spread of COVID-19 have been. It also helps to anticipate likely case numbers and further prepare the health system.

Citation: David J Price, Freya M Shearer, Michael Meehan, Emma McBryde, Nick Golding, Jodie McVernon, James M. McCaw. Estimating the case detection rate and temporal variation in transmission of COVID-19 in Australia. Technical report, posted online 14 April 2020. Access here.

Key messages

  • We adapted and applied the method developed by colleagues at the London School of Hygiene and Tropical Medicine that uses the Case Fatality Rate in a region (adjusted for cases with known outcomes) to provide estimates of the symptomatic case detection rate in Australia. We note that LSHTM added Australia to their analysis on 1 April. The present authors have since updated the analysis, including the ability to estimate a time-dependent detection rate, at national level and for each state/territory.
  • As of 9th April 2020, our estimate of the symptomatic case detection rate for Australia is 93% (95% CI 77–100%). The corresponding estimates for each state/territory are all greater than 80% (Figures 1 and 2).
  • Analyses were performed to identify temporal changes in the effective reproduction number (Reff) during the early course of the COVID-19 pandemic in each Australian state/territory.
  • These analyses produced broadly consistent results showing that the effective reproduction number is likely less than 1 in NSW, VIC, QLD, SA, and WA as of 5 April 2020 (Figures 3–5). It should be noted that these estimates are averaged across the whole of each jurisdiction, and may reflect Reff >> 1 in a number of localised settings and Reff << 1 elsewhere.
  • Reff is estimated to be above 1 in TAS, which should be interpreted with caution given the small cumulative number of cases and the large relative increase in cases recently reported (32 cases reported between 10 and 12 April).

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