China’s disease control authority said on Saturday that contact with frozen food packaging contaminated by living new coronavirus could cause infection.

The conclusion came as the Chinese Center for Disease Control and Prevention (CDC) detected and isolated living coronavirus on the outer packaging of frozen cod during efforts to trace the virus in an outbreak reported last week in the city of Qingdao, the agency said on its website.

The finding, a world first, suggests it is possible for the virus to be conveyed over long distances via frozen goods, it said.

Two dock workers in Qingdao who were initially diagnosed as asymptomatic infections in September brought the virus to a chest hospital during quarantine due to insufficient disinfection and protection, leading to another 12 infections linked to the hospital, authorities said last week.

However, the CDC`s latest statement does not show solid proof that the two workers in Qingdao caught the virus from the packaging directly, rather than contracting the virus from somewhere else and then contaminating the food packaging they handled, said Jin Dong-Yan, a virology professor at the University of Hong Kong.

The CDC said no instance had been found of any consumer contracting the virus by having contact with frozen food and the risk of this happening remained very low.

Nonetheless, it advised that workers who handle, process and sell frozen products should avoid direct skin contact with products that could possibly be polluted.

Staff should not touch their mouth or nose before taking off work garments that could possibly be contaminated without washing their hands and should take tests regularly, the agency said.

Prior to the CDC`s latest findings genetic traces of the virus had been found in some samples taken from frozen food or food packaging, but the amount of virus was low and no living virus was isolated, the agency said.

Only living virus can infect people, while samples containing dead virus could also test positive for virus traces, Jin said.