China’s capital found a Covid-19 cluster among cold chain workers on Wednesday, the latest sign the country is seeing more infections resulting from a controversial claim of transmission through contaminated goods.

Five people who worked at a cold chain storage facility in the Fangshan district of Beijing tested positive for Covid, with genetic sequencing showing three of them were infected by the delta variant, Beijing officials said at a briefing on Wednesday. The refrigeration facility also deals with imports, and the workers who tested positive hadn’t left the city in the past two weeks, they added.