Here's what's new in the outbreak linked to an emerging virus in China

More than 4,500 cases of a new viral respiratory illness have been confirmed since an outbreak began last month in the Chinese city of Wuhan. Scientists have identified the illness as a new kind of coronavirus. Coronaviruses are a large family of viruses, some of which cause the common cold. Others have evolved into more severe illnesses, such as SARS and MERS, although so far the new virus does not appear to be as deadly or contagious. Symptoms of the new virus include fever, cough and shortness of breath.

WHAT'S NEW:

- The virus has killed more than 100 people. China has cut off access to Wuhan and 16 other cities in Hubei province to try to prevent people from spreading it, trapping more than 50 million people.

- The United States was among several other nations airlifting citizens out of Wuhan. Hong Kong's leader said it will cut all rail links to mainland China and halve the number of flights.

- U.S. health officials moved to expand their checks of international travelers for signs of the virus, but they stressed the risk to Americans remains very low.

- The virus is posing a threat to the fragile world economy. China, with the world's No. 2 economy, was decelerating even before the virus hit. The virus is drawing comparisons to the SARS outbreak, which battered the economies of China and Hong Kong in 2003. Today, China represents an even bigger piece of the pie: 16% of global output now, compared with 4% in 2003, according to the World Bank. (AP)