Estimating the case detection rate and temporal variation in transmission of COVID-19 in Australia:Technical Report 14th April 2020

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).