Experts from the WHO and China conducted an investigation into the coronavirus' origins in Wuhan.
The investigation bolstered findings from studies that suggested the virus was circulating in China and Europe months before officials confirmed the first cases.
One study found that some people in the US had coronavirus antibodies in December 2019.
A growing body of evidence suggests the coronavirus was spreading globally months before the first cases in a Wuhan market captured global attention last December.
The team assessed medical records from more than 230 clinics across Hubei - the province where Wuhan is located - to look for clues. More than 90 patients in the province were hospitalized with pneumonia or coronavirus-like symptoms in October and November 2019, the Wall Street Journal reported Wednesday.
This finding lends credence to other research from China that shows people were getting sick in Wuhan in November and early December. One analysis, based on satellite images of Wuhan hospitals and online searches for COVID-19 symptoms in the area, suggested the virus may have started circulating there as early as late summer.
A study from Milan's National Cancer Institute also found that four of Italy's coronavirus cases dated back to October 2019. Another study suggests the virus reached the US' West Coast in December 2019.
Although pinpointing the exact date of the virus' first jump from animals to people is impossible without more data, these findings suggest the pandemic's December anniversary is arbitrary.
The virus was spreading in Wuhan before the December
Wuhan public-health officials initially told the WHO about a mysterious illness that would later be named the novel coronavirus on December 31, 2019.
But government records show China's first coronavirus case happened on November 17, 2019, according to an investigation by the South China Morning Post.
According to the SCMP, Chinese medical experts pinpointed 60 coronavirus cases from November and December by reanalyzing samples taken from patients seen during that time. That analysis showed that a 55-year-old from Hubei was the first known case of COVID-19 in the world, though the disease hadn't been identified at that time.
Prior to the January WHO investigation, Chinese authorities worked to sample blood from 92 people in Hubei who were hospitalized with coronavirus-like symptoms prior to the start of the pandemic.
They sampled blood from two-thirds of those patients that to check for coronavirus-specific antibodies, which would indicate the patients had previously been infected with the virus. All of the samples tested negative for those antibodies, the Wall Street Journal reported.
The remaining one-third of those 92 patients had either died or refused to participate in antibody testing.
The negative results may not mean those people didn't have COVID-19. Antibody levels do decrease over time, particularly after mild cases. But those patients were also hospitalized, suggesting a more severe illness.
"Antibodies do clear. The levels go down, but less so in cases of severe infection," Marion Koopmans, a virologist on the WHO team, told the Wall Street Journal. "From what we know about serology, out of 92 cases you would at least have some positives."
A study from did find more people were visiting Wuhan hospitals in the latter half of 2019. The study authors used satellite imagery of the city to measure traffic to six city hospitals. They saw an uptick starting in August 2019, which peaked six months later. This timeline coincided with an increase in online search traffic for terms like "diarrhea" and "cough."
The Wuhan market was not the origin of the pandemic
Among the 41 coronavirus cases, Wuhan first reported, many were people who visited or worked at the city's Huanan Seafood Wholesale Market.
The WHO team confirmed the virus didn't make its initial jump from animals to humans at the Huanan market. Evidence suggests the virus was circulating elsewhere in Wuhan before the market outbreak happened, Liang Wannian, a member of China's National Health Commission who assisted with the WHO investigation, said in a press conference Tuesday.
A May investigation also led the Chinese Center for Disease Control and Prevention to rule the market out as the origin place of the outbreak. That's because none of the animals there tested positive for the virus.
Most likely, the market was simply the site of an early superspreader event, with one sick person infecting an atypically large number of others. Superspreader events around the world have created clusters of infections that cropped up almost overnight.
Research suggests the virus was in Italy in the fall of 2019
Italy recorded its first official coronavirus case in Lombardy on February 21, 2020. Yet a recent study found coronavirus antibodies in blood samples collected from 23 Italians in September 2019 and 27 in October 2019.
"Our results indicate that SARS-CoV-2 circulated in Italy earlier than the first official COVID-19 cases were diagnosed in Lombardy, even long before the first official reports from the Chinese authorities, casting new light on the onset and spread of the COVID-19 pandemic," the authors wrote. (SARS-CoV-2 is the clinical name of the virus.)
A study conducted by Rome's Department of Environment and Health supports that conclusion: Researchers found the coronavirus' genetic material in sewage samples from Milan and Turin dating back to December 18, 2019.
Spain and France also found clues that the virus was circulating in 2019
In May, doctors at a Paris hospital discovered that patients they'd treated for pneumonia on December 27, 2019, had been sick with COVID-19. France didn't record its first official case until January 24, however.
In Spain, meanwhile, researchers from the University of Barcelona found evidence of the coronavirus in city sewage samples collected in mid-January 2020, six weeks before the country's first official case.
Surprisingly, a sewage sample collected on March 12, 2019, also tested positive for traces of the coronavirus. But testing wastewater isn't a perfect way to detect outbreaks, as Claire Crossan wrote in The Conversation. So it's possible that the March sample had been contaminated during the study.
By December 2019, the virus had reached the US
Research in the US, too, offers evidence that the virus had gone global before humanity even knew it existed.
The US recorded its first coronavirus case on January 20, 2020. But according to one study, the virus had reached the Pacific Northwest at least a month earlier. Blood samples collected by the American Red Cross in nine states, including California, Oregon, and Washington, showed that some Americans had coronavirus antibodies as early as December 13, 2019.
Antibodies are an imperfect measure of the outbreak since some research suggests our immune systems can create antibodies that recognize the new coronavirus in response to some common colds. Antibody tests can also yield false positives.
Yet in the past, scientists successfully used retrospective antibody studies to trace the origins of SARS and Middle East respiratory syndrome (MERS) - both coronaviruses. Virologists found antibodies specific to SARS in civet cats, and antibodies specific to MERS in camels, which is how they determined those to be each virus' animal progenitor.
Further examination of blood samples taken in 2019 could be the best way to find out when this pandemic really began.
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