COVID-19: could CT provide the best population level biomarker? Incidental COVID-19 in major trauma patients suggests higher than predicted rates of infection in London

•It is not known how many people have had Covid-19 since many will be asymptomatic.•Major trauma patients are an unselected group of the general population.•Unsuspected cases emerged in early February, and decreased 2 weeks post lockdown.•By the end of April we estimate 45.4% of the London population had been infected.•This technique can track the pandemic and provide early warning of surges. AIMTo evaluate incidental findings in major trauma...