Seroprevalence of SARS-CoV-2-specific antibodies in Sydney, Australia following the first epidemic wave in 2020


Heather F Gidding, Dorothy A Machalek, Alexandra J Hendry, Helen E Quinn, Kaitlyn Vette, Frank H Beard, Hannah Shilling, Rena Hirani, Iain B Gosbell, David O Irving, Linda Hueston, Marnie Downes, John B Carlin, Matthew NV O’Sullivan, Dominic E Dwyer, John M Kaldor and Kristine Macartney

Medical Journal of Australia, published online11 November 2020. 

Objectives, Setting, Participants: To estimate SARS-CoV-2-specific antibody seroprevalence among three subpopulations in Sydney (20-39-year-old women undergoing antenatal screening, 20-69-year-old plasmapheresis blood donors, and people of all ages having blood tests at selected diagnostic pathology services—general pathology) following the first epidemic wave of COVID-19 in Australia.

Design: Cross-sectional, involving de-identified residual blood specimens from public and private laboratories and Australian Red Cross Lifeblood collected April to June 2020, sampled by geographic location across 10-year age groups.

Main outcome measure: Proportion of participants in each subpopulation testing positive for anti-SARS-CoV-2-specific IgG antibody after adjustment for test sensitivity and specificity.

Results: Of 5,339 specimens, 38 were positive; there were no apparent patterns by age group, sex, or geographic area. Adjusted seroprevalence estimates were 0.15% (95% credible interval [CI] 0.04-0.41%) for people of all ages having a general pathology blood test, 0.79% (95% CI: 0.04-1.88%) for women aged 20-39 years undergoing antenatal screening and 0.29% (95% CI: 0.04-0.75%) for blood donors aged 20-69 years. When restricted to 20-39 year olds, the age group common to all three collections, estimates were 0.24% (95% CI: 0.04-0.80%) for general pathology, 0.79% (95% CI: 0.04-1.88%) for antenatal screening and 0.69% (95% CI: 0.04-1.59) for blood donors.

Conclusions: Seroprevalence well under 1% in all three subpopulations indicates limited community transmission during the first COVID-19 epidemic wave in Sydney. These findings indicate early and successful control of COVID-19, but also highlight the need to maintain efforts to mitigate further transmission.