Researchers using satellite data say the coronavirus outbreak in China may have started much sooner than reported.

A new Harvard Medical School study found that there was up to a 90% increase in hospital automobile traffic in the fall of 2019 compared to the previous year, and that at Wuhan Tongji Medical University, located in the city where the virus was believed to originate, the spike in car traffic was noted as early as mid-September.

Chinese officials did not notify the World Health Organization until December 31 that a new pathogen had been spreading in Wuhan, according to ABC News. Dr. John Brownstein, who led the Harvard study, added that the dramatic increase in hospital traffic also coincided with an increase in internet searches on symptoms that would later be associated with the coronavirus, such as “diarrhea” and “cough.”

“What we’re trying to do is look at the activity, how busy a hospital is,” Brownstein said. “And the way we’re trying to do that is by counting cars that are at the hospital. So, more cars in a hospital, the hospital’s busier, likely because something’s happening in the community, an infection is growing, and people have to see a doctor.”

RS Metrics, a firm that analyzes satellite imagery to detect changes in life and business patterns, used a similar technique employed by the Central Intelligence Agency to figure out what’s happening on the ground.

“At all the larger hospitals in Wuhan, we measured the highest traffic we’ve seen in two years during the September to December time frame,” Tom Diamond, president of RS Metrics told ABC News.

This is not the first time China has been criticized for suppressing information. The Associated Press said that six days after Chinese officials determined they faced an epidemic, there was a mass banquet in the city of Wuhan, the epicenter of the disease, for tens of thousands of people. President Xi issued a warning to the public on the seventh day, Jan. 20, but by that time over 3,000 people had been infected.