ROME — A study by Italy’s National Institute of Health has found that the new coronavirus was in circulation in wastewater in the northern cities of Milan and Turin in December 2019, at least two months before the virus was confirmed to have spread locally in the population.

The study, released Thursday, was based on 40 water samples collected as part of regular checks from sewage treatment plants in northern Italy from October 2019 to February 2020. It showed the virus that causes COVID-19 in Dec. 18 samples from Milan and Turin, while earlier samples were negative.

“This research can contribute to understanding the beginning of the circulation of the virus in Italy,” the institute said in a statement.

The research has so far not linked any confirmed cases to the virus’ earlier presence, but researchers have proposed using the system to monitor the presence of the new coronavirus in water systems in a bid to help identify any possible new outbreaks.

A pilot monitoring system will launch next month in tourist destinations, in preparation for wider monitoring ahead of a possible new spike in contagion next fall, the institute said.