Colchester and Tendring are two of the latest areas to join a major coronavirus testing expansion designed to find asymptomatic carriers of the illness.
It is believed that a third of all people who have Covid-19 do not show any symptoms, meaning they could be unwittingly spreading the disease.
As a result, rapid and regular testing for people without symptoms is being made available in the next week, with Essex authorities among the latest to sign up.
Councils will be encouraged to target testing at people who are unable to work from home during the national lockdown.
Health secretary and West Suffolk MP Matt Hancock said: “With roughly a third of people who have coronavirus not showing symptoms, targeted asymptomatic testing and subsequent isolation is highly effective in breaking chains of transmission.
“We are now expanding this offer to every local authority across the country, and asking testing to be targeted on workers who cannot work from home during this national lockdown, while asking employers to work with us to scale up workforce testing.
“Lateral flow tests have already been hugely successful in finding positive cases quickly – and every positive case found is helping to stop the spread - so I encourage employers and workers to take this offer up.
"We must all do all we can to stop the spread of Covid, right now.”
Regular, rapid testing is already available to many critical workers, such as NHS and care home staff.
Secondary schools have set up testing sites and have started to test staff and pupils who remain in school, such as the children of critical workers, or vulnerable children.
Primary schools will start to receive their test kits shortly for the weekly testing of their staff.
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