Classified Chinese government data suggests that one-third of coronavirus cases in the country were asymptomatic "silent carriers," according to the South China Morning Post, the English-language paper in Hong Kong.

Why it matters: Because of the high number of asymptomatic cases, China and South Korea started testing people who had close contact with a patient — regardless of whether they had flu-like symptoms.

This testing standard may explain how the two Asian countries have slowed the spread of the virus. Hong Kong is testing airport arrivals in the city, even if travelers have no symptoms.

By the numbers: "More than 43,000 people in China had tested positive without immediate symptoms by the end of February and were quarantined," SCMP reports.

The big picture: The number of infections is rapidly rising in most European countries and the United States, where for the most part only those with symptoms are being tested.

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