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COVID-19 patients may be contagious with coronavirus two to three days before their symptoms show, according to a research study in China.
The research was published Wednesday in the journal Nature Medicine. “Patients with the respiratory disease COVID-19 may begin to shed, or excrete, infectious SARS-CoV-2 coronavirus 2–3 days before the first symptoms appear,” the researchers explain, in a statement emailed to Fox News.
Researchers warn that the results could have major implications on measures taken to control the spread of coronavirus.
“Several factors can affect the efficacy of control measures designed to prevent the spread of SARS-CoV-2,” they said, in the statement. “These include the time between successive cases in a chain of transmission (serial interval) and the period between exposure to an infection and the appearance of symptoms (incubation period). If the serial interval is shorter than the incubation period, this would indicate that transmission may have happened before overt symptoms develop.”
The research, which was led by Eric Lau of the University of Hong Kong, involved 94 patients with COVID-19 admitted to Guangzhou Eighth People’s Hospital in China.
“Throat swabs were collected from these patients from when symptoms first appeared until 32 days later,” they explained, in the statement. “In total, 414 swabs were analyzed, and the authors found that the patients had the highest viral load at the onset of symptoms.”
Researchers also modeled COVID-19 infectiousness profiles from a different sample of 77 "transmission pairs" from publicly available data. In the transmission pairs, one patient was highly likely to have infected the other.
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“From here, the authors inferred that infectiousness started 2.3 days before symptoms appeared and peaked at 0.7 days before their appearance,” they said. “They estimated that 44% of secondary cases were infected during the pre-symptomatic stage, with infectiousness predicted to decrease quickly within 7 days.”
The study’s authors note, however, that the research depended on patient recall of the onset of symptoms. This, they caution, may have influenced the results, as there may be a delay in the recognition of the first symptoms.
Separately, a report from the Centers for Disease Control and Prevention recently warned that presymptomatic coronavirus patients can spread illness for one to three days before showing signs.
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The coronavirus first emerged in December in the Chinese city of Wuhan. As of Wednesday morning, 2 million coronavirus cases have been diagnosed worldwide, at least 83,355 of which are in China. The disease has accounted for at least 128,071 deaths around the world, including more than 3,000 in China.
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As of Wednesday morning, at least 609,696 coronavirus cases have been diagnosed in the U.S., where it has accounted for at least 26,059 deaths.
Fox News’ Jonathan Serrie and Madeline Farber contributed to this article.
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