ARI SHAPIRO, HOST:
Today health officials announced the first U.S. patient with a new virus, a type of coronavirus. It can cause severe respiratory problems, including pneumonia. This patient lives in Washington state. He tested positive for coronavirus after visiting the city of Wuhan, China. Nearly 300 people there have already gotten sick. NPR's Nurith Aizenman has more on the disease and how it's spreading.
NURITH AIZENMAN, BYLINE: This outbreak in China has been going on for at least a month and a half, but experts still have some basic questions.
MATTHEW FRIEMAN: First question is - we don't know where the virus is coming from.
AIZENMAN: Matthew Frieman is a virologist with the University of Maryland School of Medicine. He notes that many people initially infected in this outbreak had visited a live animal market in Wuhan. That suggests they caught the virus through contact with animals there, which is the typical path for new strains of this type of pathogen, part of a family called coronaviruses.
FRIEMAN: The coronavirus family has been found in bats.
AIZENMAN: Which can then spread it to other species that people tend to have more contact with. That's what sparked a massive coronavirus outbreak in Asia back in 2002 that was called severe acute respiratory syndrome, or SARS.
FRIEMAN: For SARS, it was these palm civet cats that were being sold in animal markets in China. And once that was identified, then the Chinese government banned the sale of civet cats.
AIZENMAN: Eventually, SARS was stamped out. But in this case, it's proving difficult to figure out what the animal reservoir is. Linfa Wang is a virologist at Duke National University of Singapore. He's just returned from a visit to Wuhan, where he says Chinese health officials may have inadvertently erased crucial evidence in their zeal to clean up that market.
LINFA WANG: They're just so nervous about their market, and they just send, you know, disinfection people and totally, you know, fumigate it - you know, gas it.
AIZENMAN: Now Chinese scientists are playing catch-up, sampling animals in other markets to see if they have the virus. Here's virologist Frieman again.
FRIEMAN: So until we know what the animal is, there potentially could still be animals being sold in markets all across China that is spilling virus over into people.
AIZENMAN: Even if officials can stop that spread, they'll still need to tackle another challenge. The virus now also appears to be spreading not just from animals to humans, but from one human to another, which raises the next big question. How? David Heymann is an epidemiologist at the London School of Hygiene and Tropical Medicine. He says one clue is that there seem to be many clusters of infected people who belong to the same family. They've had intense contact with an infected person.
DAVID HEYMANN: Touching patients and then contaminating yourself by not having washed hands - it doesn't seem that the current virus spreads very easily face-to-face, like with a cough or a sneeze.
AIZENMAN: But Heymann adds we also don't know what share of infections happened through these family clusters. Take the new case in Washington state. That patient says he didn't visit any markets, and he doesn't recall coming into contact with anyone who was ill. Another recent troubling development - at least 15 health workers in Wuhan have been infected with a new coronavirus.
HEYMANN: And that's always an evil omen.
AIZENMAN: Hospital workers have contact with so many sick people, Heymann says. When they get sick, they can really amplify an infection.
Nurith Aizenman, NPR News. Transcript provided by NPR, Copyright NPR.