June 9 (UPI) -- The COVID-19 outbreak may have started in Wuhan, China, in August 2019 -- at least three months earlier than previously thought -- according to an analysis by researchers at Harvard University.
The findings, based on satellite images of city streets and search engine use among local residents, show a marked increase in traffic outside five hospitals in Wuhan from late August to December.
This coincides with a spike in online searches for symptoms like "cough" and "diarrhea," the researchers said.
Chinese officials have refuted the findings, calling them "ridiculous."
"I think it is ridiculous, incredibly ridiculous, to come up with this conclusion based on superficial observations such as traffic volume," Chinese Foreign Ministry spokeswoman Hua Chunying said during a press briefing Tuesday, the BBC reported.
The analysis has been posted online and has not yet been peer-reviewed, meaning it hasn't been evaluated by independent experts for accuracy.
Until now, Chinese officials and the World Health Organization have maintained that the new coronavirus, SARS-CoV-2, first appeared in Wuhan in November. Health officials in Wuhan reported an unusual cluster of pneumonia cases to the WHO on Dec. 31.
Since then, nearly 7.2 million people have been infected globally, including almost 2 million in the United States, according to Johns Hopkins University.
To reach their conclusion, the Harvard researchers examined commercial satellite data from outside five hospitals in Wuhan, comparing images from late summer and fall 2018 to the same period in 2019.
Increases in traffic and parked cars were found at all five hospitals, including one that showed a 67 percent increase from year to year, researchers said.
At the same time, online searches for words associated with the symptoms of COVID-19 on the Chinese search engine Baidu began to increase in late summer -- before rising dramatically in late November.
Genetic analyses of coronavirus strains circulating globally also have indicated that the virus first emerged late last year, said Dr. Yonatan Grad, an assistant professor of immunology and infectious diseases at Harvard T.H. Chan School of Public Health, who was not part of the traffic and search engine analysis.
"So these findings run counter to the genetic data," Grad said during a call with reporters Tuesday.
However, he said, "having an understanding of the timing in relation to the cases, and the mitigation efforts will help us understand the impact of those mitigation efforts, and which mitigation efforts had impact on the spread of the virus and which did not."