The research was led by Dr John Brownstein, a Harvard Medical School professor, and included researchers from Boston University and Boston Children's Hospital.
It looked at satellite imagery of Wuhan from 2019 and compared it to shots taken in 2018. The technique is similar to that used by the Central Intelligence Agency.
Researchers obtained close to 350 images captured by private satellites. Around a third were usable because they had no smog, tall buildings or clouds in the way.
They counted the number of cars parked at Wuhan hospitals at points in the northern autumn of 2019 and compared them with images in 2018.
Zhongnan Hospital of Wuhan University had 506 cars parked one day in October 2018 but 640 cars parked one day in October 2019.
At Wuhan Tongji Medical University the number almost doubled, from 112 cars one day in October 2018 to 214 cars one day in September 2019.
Similar was seen at Wuhan Tianyou Hospital. One day in October 2018 there were 171 cars parked at the hospital. Around a year later the number of cars was 285.
In an attempt to find another data source the team also looked at searches on Baidu, a Chinese search engine, from the Wuhan region.
They found last year searches for "cough" and also "diarrhea" - a symptom believed to be more common with Covid-19 than the flu - spiked in that period.
Researchers accept the evidence is circumstantial, but believe it adds weight to suggestions an outbreak happened in Wuhan earlier than thought.
"Something was happening in October," Brownstein told ABC News. "Clearly, there was some level of social disruption taking place well before what was previously identified as the start of the novel coronavirus pandemic."
Brownstein argued that the number of cars parked at a hospital was an indication of how busy the hospital was at that point in time. Therefore a car park considerably busier than the year before suggests illness in the area could be spiking.
The study has been submitted for the journal Nature Digital Medicine and is under peer review. One academic warned ABC News about over-interpreting the results. It is possible there are other reasons for the more full car parks.
The South China Morning Post, based in Hong Kong, has reported that the first Covid-19 case in China could be traced back to Nov 17 2019, citing Chinese data.
Should the outbreak have emerged in October, or even earlier, it would raise fresh questions about why the Chinese Government did not alert the world sooner.
US President Donald Trump has been fiercely critical of the Chinese Government over its handling of Covid-19, including claiming it has not been transparent about how the virus emerged.
China's Government has vehemently defended its coronavirus response in a lengthy report, saying that through "painstaking efforts and tremendous sacrifice" it triumphed in a "test of fire".
