Covid-19 may have been spreading through China as long ago as August 2019, a new study from Harvard Medical School reported.
Using satellite images of hospital travel patterns and search engine data from Wuhan where the virus was first detected, the paper suggests that people may have been suffering from the condition long before it was officially declared in December 2019.
"Increased hospital traffic and symptom search data in Wuhan preceded the documented start of the SARS-CoV-2 pandemic in December 2019," the research said, using the official medical name for the novel coronavirus.
"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, led by Elaine Okanyene Nsoesie of the Department of Global Health at Boston University School of Public Health and Benjamin Rader of the Computational Epidemiology Lab at Boston Children’s Hospital, said.
While the Huanan Seafood Market in Wuhan has been linked to many of the first patients suffering from the coronavirus in December 2019, the paper points to other studies that found at least 14 early cases had no tie to the location, including the first known case. This, it suggested, “leaves open the possibility of alternative points of origin and infection”.
“This hypothesis is supported by emerging epidemiologic and phylogenetic evidence indicating that the virus emerged in southern China and may have already spread internationally, and adapted for efficient human transmission, by the time it was detected in late December,” the paper said.
The study said that imaging showed busier than usual hospitals in the area and increase in searches for symptoms now associated with Covid-19.
“We observe an upward trend in hospital traffic and search volume beginning in late summer and early fall 2019,” the researchers said. “While queries of the respiratory symptom ‘cough’ show seasonal fluctuations coinciding with yearly influenza seasons, ‘diarrhoea’ is a more Covid-19 specific symptom and only shows an association with the current epidemic. The increase of both signals precedes the documented start of the Covid-19 pandemic in December, highlighting the value of novel digital sources for surveillance of emerging pathogens.”
The satellite images showed that while there has been a general increase in traffic at hospitals in the city over the past few years, there was a steep increase from August 2019.
This then tallied with a surge in local online searches for symptoms including “diarrhoea” and “cough” – both associated with Covid-19. While it highlights that the search term “cough” has seasonal peaks associated with other flues and influenzas, “both search query terms show a large increase approximately 3 weeks preceding the large spike of confirmed Covid-19 cases”.
“While we cannot confirm if the increased volume [of searches and trips to hospitals] was directly related to the new virus, our evidence supports other recent work showing that emergence happened before identification at the Huanan Seafood market," it said. "These findings also corroborate the hypothesis that the virus emerged naturally in southern China and was potentially already circulating at the time of the Wuhan cluster."