A controversial study from Harvard Medical School, Boston University of Public Health, and Boston Children’s Hospital has claimed that Covid-19 may have been in Wuhan, China as early as August 2019, months before the first cluster of cases were reported to the World Health Organization in late December.
The virus was first linked to the Wuhan seafood market before later studies found evidence that the virus may have emerged at least a few weeks earlier than the initial timeline suggested. The new study has looked at satellite images and Internet search histories to investigate whether it might have been even earlier than that.
The researchers looked at satellite imagery of hospital parking lots and search queries relating to now known symptoms of Covid-19 on the Chinese search engine Baidu from last year. The research, which has not yet been peer-reviewed, showed an increase in searches relating to symptoms such as "cough" and “diarrhea,” neither of which were seen "in previous flu seasons or mirrored in the cough search data".
The team used the search term "diarrhea" rather than just cough to attempt to eliminate people with other illnesses, such as influenza. "Gastrointestinal symptoms are a unique feature of Covid-19 disease and may be the chief complaint of a significant proportion of presenting patients," the researchers write in the paper.
Analysis of satellite images of hospital car parks showed an increase in traffic in October and November.
"While we cannot conclude the reason for this increase, we hypothesize that broad community transmission may have led to more acute cases requiring medical attention, resulting in higher viral loads and worse symptoms," the authors write.
However, the study has been rejected by Chinese officials. “To derive these conclusions from phenomena such as road vehicle traffic [...] is extremely preposterous,” Chinese foreign ministry spokesperson Hua Chunying said Tuesday.
It's been met with some criticism from the scientific community too.
"Using search engine data and satellite imagery of hospital traffic to detect disease outbreaks is an interesting idea with some validity," Professor Paul Digard, Chair of Virology at the University of Edinburgh said. "However, it’s important to remember that the data are only correlative and (as the authors admit) cannot identify the cause of the uptick."
"By focussing on hospitals in Wuhan, the acknowledged epicentre of the outbreak, the study forces the correlation," Prof Digard added. "It would have been interesting (and possibly much more convincing) to have seen control analyses of other Chinese cities outside of the Hubei region.”