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Symptoms of infection include a high fever, difficulty breathing and lung lesions. Milder cases may resemble the flu or a bad cold, making detection very difficult. The incubation period — the time from exposure to the onset of symptoms — is believed to be about two weeks. Little is known about who is most at risk. Some of the nine patients who have died also suffered other illnesses. (Zraick, 1/21)

Health officials around the world are keeping a close watch on an outbreak of a new virus in China. In response, governments are stepping up surveillance of airline passengers arriving from the affected area to try to prevent the virus from spreading. Here's what you should know about the illnesses. (1/21)

The World Health Organization on Tuesday raised the possibility that the new virus spreading in parts of China may be transmitting in an ongoing, sustained manner between people — which, if confirmed, would make it significantly more difficult to stop. The agency’s Western Pacific Regional office, which covers China and neighboring countries, said on Twitter that new information “suggests there may now be sustained human-to-human transmission.” (Branswell, 1/21)

Coronaviruses are a group of viruses that can cause a range of symptoms including a runny nose, cough, sore throat and fever. Some are mild, such as the common cold, while others are more likely to lead to pneumonia. They're usually spread through direct contact with an infected person. The coronavirus gets its name from the crown-like spikes on its surface, according to the CDC. (Corona is Latin for crown.) Including the newly identified form of the virus, there are a total of seven coronaviruses that can infect humans, the CDC says. Other well-known coronaviruses include SARS and MERS. (Edwards, 1/21)

Public health officials around the world are on alert because the new infection is caused by a coronavirus, from the same family that caused outbreaks of SARS and MERS, killing hundreds of people in dozens of countries. The W.H.O. has already advised governments to be prepared for the disease, to be vigilant and ready to test anyone with symptoms like cough and fever who has traveled to affected regions. Air travel is expected to surge as the Lunar New Year approaches this weekend. (Grady, 1/22)

U.S. officials are weighing the benefits and risks of proposed experiments that might make a dangerous pathogen even worse — but the details of that review, and the exact nature of the experiments, aren't being released to the public. Later this week, officials are to hold a meeting in Bethesda, Md., to debate how much information to openly share about this kind of controversial work and how much to reveal about the reasoning behind decisions to pursue or forgo it. (Greenfieldboyce, 1/21)