The coronavirus that the World Health Organization has named COVID-19 has infected 1,716 Chinese health workers and killed six of them, Chinese authorities said Friday.

"The duties of medical workers at the front are indeed extremely heavy; their working and resting circumstances are limited, the psychological pressures are great, and the risk of infection is high,” Chinese Health Commission Vice Minister Zeng Yixin said at a news conference.

Officials reported 5,090 new cases in mainland China, bringing the total to nearly 64,000. The upper respiratory infection has claimed 1,380 lives, making it deadlier than the SARS outbreak of 2003.

So far, 15 U.S. residents have been infected, in most cases while traveling in the area of Wuhan, China, where the virus is believed to have emerged in late December. No cases have been confirmed in Pennsylvania or New Jersey, but more U.S. cases are expected among other travelers who have returned from China and remain under quarantine, the CDC said.

Experts say that for us, the regular seasonal flu — which has killed more than 10,000 Americans so far this season — poses much more of a risk here than the coronavirus. Here’s what you need to know about this new virus.

Who is getting it worldwide?

Laboratory testing has confirmed the virus has sickened at least 64,435 people worldwide, most of them in China. But this week, the Chinese government broadened its definition of how cases are being identified, adding another 14,000 cases to the total despite a lack of lab confirmation.

These additional cases appear to have been identified solely as a result of patient symptoms and exposure, as labs struggle with a backlog in testing samples. Still more patients likely have been infected but not identified, because they suffered milder symptoms and did not seek treatment.

What about in the United States?

While most U.S. residents with the new coronavirus became infected while traveling in China, two people — one in Chicago, one in California — contracted it from family members who had traveled in China. The 15 confirmed cases are in Wisconsin, Arizona, California, Illinois, Massachusetts, and Washington.

So far, health departments in 36 states — including Pennsylvania and New Jersey — have reported hundreds of patients to the U.S. Centers for Disease Control and Prevention as possible cases, including the 15 patients confirmed to have the illness. Most of the rest have tested negative for the virus, though some results are pending.

How are patients with suspected virus identified?

The CDC is asking health departments to use a broad definition when identifying possible cases: anyone with fever or respiratory symptoms such as a cough who also meets one of these two additional criteria: travel to China within the previous 14 days or close contact with a patient with a confirmed disease.

But I heard somebody who had no symptoms gave somebody else coronavirus?

That report out of Germany, published Jan. 30 in the New England Journal of Medicine, has been debunked, health officials say. On further investigation — including talking to the patient, Science magazine reported on Monday — it turned out that a Chinese businesswoman traveling to her company headquarters in Bavaria, actually did have coronavirus, but her symptoms were mild and she was taking medicine to keep her fever down, German health officials confirmed this week.

This doesn’t mean asymptomatic transmission is impossible — people can “shed” certain viruses they are carrying without showing symptoms. But according to the WHO, people who cough or sneeze are more likely to spread the virus.

Can a pregnant woman transmit the virus to her baby?

A report in a state-run Chinese newspaper said an infant was diagnosed 30 hours after birth, raising fears of transmission in the womb. This possibility has not been confirmed, and Chinese media has also reported an anecdotal case of a woman infected with the coronavirus who gave birth to an uninfected baby.

A study published Feb. 12 in the Lancet followed nine pregnant women in Wuhan who had pneumonia caused by coronavirus infections. The study concluded there is currently no evidence that the virus can be passed from mother to child late in pregnancy.

In any case, it is possible for a mother to pass a disease-causing virus to her baby immediately before or after birth. This “perinatal transmission” can occur across the placenta, in the breast milk, or through direct contact during labor and delivery. The Zika and AIDS viruses, among others, have been transmitted this way.

What are physicians supposed to do if they encounter a suspected case of coronavirus?

The Philadelphia Department of Public Health has sent advisories to area physicians on the protocol when caring for such patients. Here’s a summary:

  • Patient is given a surgical mask and moved to a private room, preferably an airborne infection isolation room.
  • Case is reported to facility’s infection specialist and the health department.
  • Testing for 2019-nCoV (the scientific name for this type of coronavirus) is coordinated through state and local health departments with the CDC. When a person is deemed to be a “2019-nCoV Patient Under Investigation,” nasal swabs and other patient samples are sent for testing at the CDC in Atlanta. State labs around the country will soon have the ability to test samples, easing the delay.

Where did coronavirus come from?

The microbe is believed to have originated in a large live-animal market in Wuhan. Genetic sequencing suggests the virus may have jumped from a bat. Evidence suggests the virus originally could be transmitted only from animal to animal, but gained the ability to “jump” from animal to human, and now is being transmitted between people.

How serious is it?

Though more than 1,300 people have died from the infection, in most cases the impact appears to be fairly mild. So far the risk appears to be low in the U.S., where there have been no deaths, the CDC says. If the Lancet’s estimate for the total number of cases is correct, the death rate from the virus is under 1%.

Who is most at risk?

As with most respiratory illnesses, health experts suspect the greatest risk is faced by older people, the very young, and anyone with compromised immune systems. However, there have been fatalities among younger, healthier people, including Li Wenliang, the 34-year-old ophthalmologist, who was reprimanded by Chinese officials after warning about the disease in December.

Evidence suggests that the virus spreads about as easily as other members of the coronavirus family — carried no more than several feet through the air by droplets from coughing or sneezing.

What are the symptoms?

Officials have urged people to consult their physicians if they have been to China — or have been in close contact with someone recently returned from China — and subsequently experience symptoms that can include fever, cough, and difficulty breathing. Evidence suggests that the virus has an incubation period as long as 14 days, meaning the time between exposure and the development of symptoms.

How is it different than the flu?

Those infected with influenza virus commonly experience muscle aches and fatigue. Those infected with the new coronavirus experience mostly respiratory symptoms, similar to pneumonia in more serious cases.

How can I protect myself?

It’s very unlikely that most Americans will encounter the coronavirus. But the CDC recommends these hygiene measures that also will help protect you from other viruses:

  • Wash your hands often with soap and water for at least 20 seconds. Use an alcohol-based hand sanitizer that contains at least 60% alcohol if soap and water are not available.
  • Avoid touching your eyes, nose, and mouth with unwashed hands.
  • Avoid close contact with people who are sick.
  • Stay home when you are sick.
  • Cover your cough or sneeze with a tissue, then throw the tissue in the trash.
  • Clean and disinfect frequently touched objects and surfaces.

If you haven’t yet had a flu shot, go get one. It won’t stop coronavirus, but you’re much more likely to encounter the influenza virus, and the vaccine can prevent or lessen illness.

Should you wear a mask?

Almost certainly not. There have been just two instances in the U.S. in which the virus was transmitted from one person to another, in both cases family members of people who had traveled in China.

And in any event, experts say many masks will not filter out the virus — except for those of high quality, such as a variety called N95. Good face masks can lower the wearer’s risk of exposure to any virus, as well as preventing the wearer from infecting others, so they are recommended in health care settings.

But generally, the CDC and WHO recommend the same protective measures you’d use to keep healthy during any cold and flu season: Wash your hands frequently, cover your sneezes, stay home if you’re sick.

What’s being done to prevent coronavirus from spreading?

Chinese officials imposed travel restrictions and closed the large animal market that is believed to be the source of the microbe. The U.S. is urging people to avoid all non-essential travel to China, and continues to screen passengers from Wuhan for signs of illness at 11 airports including Newark and New York. Schools and universities around the country have imposed travel restrictions for exchange students and study-abroad programs.

What if I have upcoming travel plans to China?

Both the State Department and the CDC have issued advisories, recommending against travel to China. But if you can’t avoid the trip, the CDC advises discussing your travel plans with your healthcare provider — particularly if you’re an older adult or if you have underlying health issues. Avoid contact with sick people and with animals, and wash your hands frequently.

Is it a pandemic?

The WHO defines pandemic as “the worldwide spread of a new disease," while an epidemic is generally defined as a disease whose spread is confined to a particular region or country.

The CDC has said it is treating the new virus as if it were a pandemic, but has stopped short of calling it that. Some Chinese officials have accused the U.S. of overreacting.

Is there a vaccine?

There is no vaccine for the new coronavirus but pharmaceutical companies are working to create one. Inovio Pharmaceuticals Inc. in Plymouth Meeting announced on Jan. 23 that it received a grant of up to $9 million to rapidly develop a vaccine. The company has partnered with Philadelphia’s Wistar Institute. Johnson & Johnson is also working on a vaccine, which the company believes will be ready for human testing in the next eight to 12 months. Gilead Sciences Inc. in California is also developing a treatment drug called remdesivir which is due to start clinical trials and which the Chinese government is attempting to seek a patent on, despite it being developed in the U.S.

Why is it called a coronavirus?

Coronaviruses are a large family of viruses, including those that cause SARS, MERS, and some forms of the common cold. They are so named because the particles have rounded protrusions on their outer edge, resembling the fringe-like corona in a solar eclipse.