Has Australia really had 60,000 undiagnosed COVID-19 cases?

A preliminary study, posted online this week by researchers at the Australian National University and elsewhere, estimates 71,000 Australians had COVID-19 by mid-July — 60,000 more than the official number of cases diagnosed by that stage.

The study involved testing 2991 elective surgery patients in 10 hospitals across four states to see whether they had antibodies against SARS-CoV-2, the virus that causes COVID-19.