The most likely date of origin, the researchers said, is Nov. 17, 2019, earlier than the first officially identified case more than a month later.
This earlier date of origin likely also impacts when the virus began to spread globally, with the first case in the United States actually occurring as early as mid-January of 2020, they said.
"Our findings provide further support for an autumn emergence of the virus [and], by mid-January, it had spread within Southeast Asia and jumped to Europe and North America," study co-author David L. Roberts told UPI in an email.
"It's a bit like a crime -- when you know when it happened, then you can start comparing it against alibis," said Roberts, head of the conservation biology department at the University of Kent in England.
Many questions remain about the origins of the coronavirus.
Although Chinese officials have said the first cases were identified among shoppers and sellers at a market in Wuhan in December 2019, reports suggest that the staff at a research lab nearby may have been infected, perhaps weeks earlier.
To help clarify the timing of the onset of the pandemic, Roberts and his colleagues repurposed a mathematical model originally developed by conservationists to identify the date of extinction of a species, based on recorded sightings.
For this analysis, the researchers reversed the method to determine the date when COVID-19 most likely originated, based on when some of the earliest known cases were reported in 203 countries.
Based on their model, the first case occurred in China between early October and mid-November of 2019, before it began spreading globally the following January, the researchers said.
In addition, the findings add to growing evidence that the pandemic arose sooner and grew more rapidly than officially -- and initially -- accepted, they said.
The first case outside of China occurred in Japan on Jan. 3, 2020, while the first case in Europe occurred in Spain nine days later, the data showed.
Meanwhile, the first case in North America occurred in the United States on Jan. 16 last year, about five days before the first official infection was reported, the researchers said.
Knowing precisely when the virus first emerged in humans "allows us to understand how long it may have been circulating undetected and therefore question our abilities to detect such outbreaks," Roberts said.
"It also allows us to critically evaluate hypotheses regarding [the] virus's origin," he said.