The novel coronavirus might have hit the Chinese city of Wuhan as early as August 2019, months before it was first reported, according to a new study in the United States.
The report published by the Harvard Medical School analysed satellite images of hospital traffic in Wuhan, where the disease is said to have originated in December last year - and search engine trends related to the virus.More: Exclusive: Videos show huge medical equipment backlog in China Coronavirus origin: Few leads, many theories in hunt for source Timeline: How the new coronavirus spread
"Increased hospital traffic and symptom search data in Wuhan preceded the documented start of the SARS-CoV-2 pandemic in December 2019," the report said.
"While we cannot confirm if the increased volume was directly related to the new virus, our evidence supports other recent work showing that emergence happened before identification at the Huanan Seafood Market."
The US-based researchers looked at satellite imagery of parking lots of six hospitals in Wuhan, five of which showed their highest relative daily volume between September and October 2019.
These findings also coincided with an uptick in queries on the Chinese search engine, Baidu, for coronavirus-related symptoms like "diarrhoea" and "cough".
On December 31 last year, China alerted the World Health Organization (WHO) to several cases of unusual pneumonia in Wuhan, a city of 11 million people.
Since then, the virus has spread to 188 countries, infecting more than seven million people and killing at least 406,000 people worldwide.
But questions still remain about the origins of the coronavirus, which researchers suspect came from the Huanan Seafood Wholesale market in Wuhan where wild animals were being sold illegally.
The study by Harvard said it found "no direct connection to the market for 14 individuals, including the first known case of COVID-19, leaving open the possibility of alternate points of origin and infection".
"Although further research is needed to validate the emergence of SARS-CoV-2, this study adds to a growing body of work on the value of digital sources as an early indicator of a disease outbreak in the context of limited integrated electronic surveillance data," the report said.
Last week, an investigation by The Associated Press news agency said China withheld vital information about the outbreak and waited more than a week before publishing the genome of the coronavirus in January.
According to the WHO, the most common symptoms of COVID-19 are fever, fatigue and a dry cough. Some patients may experience aches and pains, nasal congestion, a runny nose, sore throat or diarrhoea.