Satellite images of Wuhan hospitals' parking lots and search engine queries from the Chinese city suggest the COVID-19 outbreak started much earlier than previously thought, according to research from Harvard Medical School, a report from Euronews said.

Researchers used more than 110 satellite images of six hospitals located in Wuhan from between January 2018 to April 2020 as well as daily data for symptom-related searches such as "cough" and "diarrhea" on Chinese search engine Baidu from Wuhan from April 2017 to May 2020.

They found that "increased hospital traffic and symptom search data in Wuhan preceded the documented start of the SARS-CoV-2 pandemic in December 2019."

They noted for instance that a "steep increase" in hospital occupancy as measured by the parking lot volume proxy was first observed in August 2019, culminating with a peak in December 2019.

August also saw "a unique increase in searches for diarrhea which was neither seen in previous flu seasons or mirrored in the cough search data".

Queries of the respiratory symptom "cough" show seasonal fluctuations coinciding with yearly influenza seasons, but "diarrhea" is a more COVID-19 specific symptom and only shows an association with the current epidemic, researchers stressed