Defining the peak: Point prevalence of SARS-CoV-2 using randomised sampling

Abstract

Since Queensland eased border restrictions to the rest of Australia on 13 December 2021, notified cases of Coronavirus disease 2019 (COVID-19) dramatically increased, with the SARS-CoV-2 Omicron variant now the most widespread variant of concern: 145,881 cases and 13 deaths were recorded in Queensland in the month following the opening of the border. For an effective public health response to a highly transmissible disease, it is important to know the prevalence in the community, but the exponential increase in cases meant that many with symptoms had difficulty getting tested. We implemented a surveillance program on the Gold Coast that used a modified randomised household cluster survey method to estimate the point prevalence of individuals with SARS-CoV-2 detected by polymerase chain reaction (PCR). The estimated point prevalence of SARS-CoV-2 detected by PCR on self-collected swabs was 17.2% on the first visit to households (22 January 2022). This subsequently decreased to 5.2% (5 February 2022) and finally to 1.1% (19 February 2022). Out of 1,379 specimens tested over five weeks, 63 had detected SARS-CoV-2 and 35 (55.6%) were sequenced. All were SARS-CoV-2 variant: B.1.1.529 (i.e. Omicron). This surveillance program could be scaled up or reproduced in other jurisdictions to estimate the prevalence of COVID-19 in the community.