A twelfth coronavirus case was reported in the US this week, as the death toll from the outbreak climbed to 491 in China and more than 24,500 diagnoses were made globally, according to public health officials.
It took the new coronavirus 48 days to infect the first 1,000 people. And Wuhan had another 132 quarantine sites with more than 12,500 beds, according to the official Xinhua News Agency.
The large number of cases in China - 24,405 cases there and 479 deaths in Hubei province until Wednesday morning - suggests that the answer will be yes, but a study in The New England Journal of Medicine describing the only confirmed asymptomatic transmission turns out to have been incorrect.
Hong Kong, which has 21 confirmed cases and one fatality, suffered 300 deaths in the Sars outbreak in 2002 to 2003.
Thousands of hospital workers in Hong Kong are striking to demand the border with mainland China be closed completely.
"People living in the USA should still not be anxious", Brown said.
So far, 22 nations have officially reported trade or travel-related measures linked to the coronavirus, which Tedros said should be "short in duration, proportionate" and reviewed regularly. Details weren't given, but milder cases have been seen in younger, healthier people.
"We don't know the source of the outbreak, we don't know what its natural reservoir is, and we don't properly understand its transmissibility or severity", Tedros said.
Zeng said the possibility "needs further study".
"But 4,000 cases or almost, 3,700 coronavirus cases confirmed in a single day, is nothing to celebrate and is certainly still a great worry", he said.
The Chinese government has virtually locked down the central province of Hubei, home to 60 million people and its capital city of Wuhan at the centre of the outbreak.
Hong Kong authorities say more than 5,000 people may have been exposed to a virus during previous voyages on a cruise ship now in quarantine. The biggest worry is the virus being imported or spread in countries with ill-prepared health systems.
The objectives of the Strategic Preparedness and Response Plan (SPRP) are to limit human-to-human transmission of the virus, especially in countries most vulnerable if they were to face an outbreak. "If there is a way that they can leave them for workout periods, for example, this would be extremely helpful in helping people manage stress levels".
More than 3,600 passengers and crew on the Hong Kong ship, the World Dream, were being screened after eight passengers from a voyage that began January 19 were diagnosed with the virus. Quarantines, the kind that public health officials advocate, are much more targeted.
The baby born Sunday in Wuhan is China's youngest case of the illness. Word of the trials had boosted the stock price of the drug's maker, American biotechnology company Gilead Sciences Inc.