According to Reuters, Italian health officials have found traces of the SARS-CoV-2 virus in sewage samples taken in December 2019, which means the virus was being transmitted in Northern Italy even before the first cases were reported in China.

The Italian National Institute of Health looked at 40 sewage samples collected from wastewater treatment plants in northern Italy between October 2019 and February 2020. An analysis released on Thursday said samples taken in Milan and Turin on Dec. 18 showed the presence of the SARS-CoV-2 virus.

“This research may help us understand the beginning of virus circulation in Italy,” said Giuseppina La Rosa, an expert in environmental wastewater at the Italian National Institute of Health who co-led the research.