For as long as the outbreak of the novel coronavirus in China has been raging, public health officials have kept their eyes on one key variable: whether the virus was continuing to spread even far away from the epicenter in Wuhan. Last week, when the World Health Organization decided against declaring the outbreak an international public health emergency, the absence of sustained human-to-human transmission outside of mainland China was a factor. At that point, only Vietnam had a coronavirus patient who hadn’t personally been to Wuhan. It was just one case.
Now there are at least four more. On Tuesday, officials in Japan, Taiwan, and Germany all reported their first cases of domestic human-to-human transmission. Thursday morning, US Centers for Disease Control and Prevention confirmed the first such incident on American soil. In each of the new cases, patients contracted the deadly disease outside China, from someone else who had recently been there. They include patients who got sick not from family members, but from people they came into contact with while working, and at least in one case, people who weren’t showing any symptoms.
So it’s no coincidence that WHO Director-General Tedros Adhanom Ghebreyesus announced he is reconvening the emergency committee in Geneva today for a new vote. At a press conference Wednesday, WHO officials told reporters his decision is based mainly on two things: the increasing number of global cases—from about 800 a week ago to more than 7,800—and the fact that the infection has now spread to people in four countries who have never been to China. “These developments in terms of the evolution of the outbreak are of great concern,” said Mike Ryan, WHO’s director of health emergencies.
“If there is evidence of sustained human-to-human spread in a new country, that really does appear to shift us into a new phase,” says Charles Chiu, an infectious disease doctor and researcher at the University of California San Francisco. We’re not there yet. But we’re close. You can think of it like a brushfire, he says. Right now, China’s on fire. And it’s sending sparks out across the globe. So far, nothing’s been catching. With these new cases, there’s starting to be some smoke. The question now is, will they get fanned into a full-on conflagration?
Not all types of domestic transmission are the same. In the case in Vietnam, a young man spent three days sharing a hotel room with his sick father, according to a case study published Tuesday in The New England Journal of Medicine. In both the US and Taiwan, men were infected by their spouses who had recently returned from work trips to China. These kinds of family clusters are to be expected with a virus that is believed to transmit through respiratory droplets, exposing people who come within six feet of an infectious individual. Public health officials have a comparatively easy time keeping track of families; the same goes for patients who infect healthcare workers. It’s the other cases, like the ones in Germany and Japan, that are more worrying.
On Tuesday, German officials reported that a 33-year-old man was infected by a colleague visiting from China while the two attended a training seminar—the first case of human-to-human transmission in Europe. Three of his coworkers are also showing symptoms and currently under medical observation. The same day, Japan confirmed its first domestic transmission: a bus driver in his 60s who lives in the prefecture adjacent to Kyoto. Within the last month, he had driven tour groups that included visitors from Wuhan.
Both instances present big challenges to public health officials trying to track down and isolate any other people who might have been exposed to the virus. The difference between catching them all and missing a few is the difference between stamping out a smoking spark and blowing it onto dry tinder. Right now, it’s still too early to say which way these will go. But trying to guess will almost certainly be part of the WHO’s latest deliberations.
Much is still unknown about how deadly the new virus really is, and how far and fast it’s capable of spreading. Based on currently available data, WHO officials said it appears to kill only about two percent of its victims—much fewer than SARS. Most infected people experience mild symptoms including fever and cough, with about 20 percent becoming severely ill.
But Chiu says this comes with a tradeoff. Infected people might not go to the doctor, leaving them undetected and invisibly infecting other people. Current estimates indicate that every individual who gets sick can spread the virus to two to three more people. “Being less deadly actually helps the virus to more successfully propagate itself,” he says. That’s why catching cases early is so important.
This week, the United States announced it is expanding the screening of travelers arriving from Wuhan, from five airports to 20 ports of entry, including some land crossings. Speaking at a press briefing Tuesday, CDC director Robert Redfield said that it’s a necessary precaution. “Our goal is to contain this virus and prevent sustained spread of the virus in our country.”
Updated 1:20pm ET: The story was updated to include more recent data on local transmission and global infections.
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