China on Tuesday rejected a Harvard Medical School study that the coronavirus may have been spreading in the country as early as August – months earlier than the authorities in Beijing admitted to the outbreak, Reuters reported. The virus, which is said to have originated in a wildlife market in the Chinese city of Wuhan, was first reported to the World Health Organization in late December.

The Harvard researchers came to the conclusion after analysing satellite images of hospital parking lots in Wuhan and search engine data about potential disease symptoms such as cough and diarrhoea. “Increased hospital traffic and symptom search data in Wuhan preceded the documented start of the SARS-CoV-2 pandemic in December 2019,” the authors said in a paper released online. “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The study, which has not yet been peer-reviewed, saw a steep increase in hospital car park occupancy in August 2019 and culminated with a peak in December 2019. “Individual hospitals have days of high relative volume in both fall and winter 2019,” the authors said. “However, between September and October 2019, five of the six hospitals show their highest relative daily volume of the analyzed series, coinciding with elevated levels of Baidu search queries for the terms ‘diarrhea’ and ‘cough’.”

Hua Chunying, a Chinese foreign ministry spokesperson, dismissed the findings when she was asked about them at a daily press briefing on Tuesday. “I think it is ridiculous, incredibly ridiculous, to come up with this conclusion based on superficial observations such as traffic volume,” she said.

Paul Digard, professor of virology at the University of Edinburgh, said that using search engine data and satellite imagery of hospital traffic to detect disease outbreaks “is an interesting idea with some validity”. However, he added that the data is only correlative and cannot identify the cause of the uptick.

Digard cautioned that the study forces correlation by focusing only on hospitals in Wuhan. “It would have been interesting – and possibly much more convincing – to have seen control analyses of other Chinese cities outside of the Hubei region,” he told Reuters.

The study gained attention at a time when United States President Donald Trump has consistently pointed to Chinese culpability in failing to contain the outbreak in its early stages. The pandemic has increased tensions between Washington and Beijing in the last few months.

More than 71.56 lakh people have been infected with the coronavirus worldwide since December, according to Johns Hopkins University, with more than 4.07 lakh global deaths.