COVID-19 was transmitted through leaked toilet waste from a sewage pipe in a previous infection cluster in a crowded residential community in Guangzhou, Guangdong province, according to an announcement on Friday.

The leak was discovered through epidemiological research on the epidemic in Guangzhou, officials said at a news conference in the city.

Two members of a family living on the second floor of a building were first confirmed with the infection. They were followed by six infected people in three families in two other adjacent buildings, said Yuan Jun, deputy director of the Guangzhou Center for Disease Control and Prevention.

A dozen samples collected from around the three buildings tested positive for the coronavirus.

Further investigation pointed to a leak in the sewage pipe from the first infected family. Because of the higher position of the building, combined with rain, toilet sewage was flushed around the other two buildings.

Samples from the shoe soles and a bicycle belonging to the four infected families tested positive. The infected people did not change shoes after returning home.

Researchers concluded that the six people in the two other buildings were infected by contact with contaminated space, Yuan said.