Revelations that a nasty strain of the coronavirus found its way out of an Adelaide hotel in a suspected case of surface transmission via a casual employee who then did a shift at a pizza parlour is cause for great concern.

It mirrors the Victorian experience as that state was launched into its deadly and disruptive second wave. There, too, one of the avenues the virus took into the wider community was via people who did casual shifts in the quarantine hotels and then in other workplaces.

South Australia is introducing weekly tests for workers at the quarantine hotels, which while a positive step won't guarantee the virus is kept confined.

Consideration must be given to ensuring those who work as cleaners, security guards and in other roles at quarantine hotels do not work shifts in other workplaces and risk spreading the virus.

By their very nature, places of quarantine are dangerous places. Every step must be taken to ensure workers, their families and the wider community are protected. If this means organising casuals get enough shifts in the quarantine hotels to negate the need to supplement income by working elsewhere, so be it.

Each week thousands of Australians are returning from COVID hot spots in the northern hemisphere so it is to be expected they bring the virus back with them. And if, as suspected, the virus is mutating into more virulent strains, our quarantine system needs to flex to meet that reality.

The concern in South Australia is that the coronavirus strain detected there takes only 24 hours to make a person to whom it is transmitted contagious. That strain was imported by a traveller returned from the UK.

Early on the pandemic, some companies with multiple offices slapped a ban on employees travelling between those workplaces. It was a commonsense measure designed to protect staff and lessen the likelihood of the virus beiong unwittingly spread between communities.

Until there is a vaccine and the population has been vaccinated - itself an enormous undertaking - every measure to prevent the spread needs to be taken. Restricting people to one workplace might be an option.