An unpublished study by Spanish virologists suggests the novel coronavirus has been around much longer than we thought.

According to Reuters, researchers at the University of Barcelona announced Friday they had detected COVID-19 in sewage samples collected in March 2019—about nine months before the disease was first reported in Wuhan, China. The team of researchers said they began testing frozen wastewater samples taken between January 2018 and December 2019. All samples reportedly tested negative for coronavirus traces, except for the March 12, 2019 sample. However, research leader Albert Bosch emphasized that the levels of SARS-CoV-2 were low.

"Barcelona receives many visitors for both touristic and professional reasons," Bosch said. "It is possible for a similar situation to have taken place in other parts of the world, and since most of the COVID-19 cases show a similar symptomatology to the flu, those cases could have been disguised as the flu."

The study has since been submitted for peer review, but independent experts say more tests and data are needed before the findings can be confirmed. Some have also pointed to the possibility of a false positive.

"When it’s just one result, you always want more data, more studies, more samples to confirm it and rule out a laboratory error or a methodological problem," said Dr. Joan Ramon Villalbi, a board member of the Spanish Society for Public Health and Sanitary Administration. "It’s definitely interesting, it’s suggestive."