Wuhan is the capital of Hubei and is the seventh-largest city in China, with a population of more than 11 million people. It has been a major transport hub of the country for centuries and known as "Nine Provinces' Thoroughfare" (九省通衢) since at least the 17th century, and the Wuhan Railway Hub is one of the four most important railway hubs in China. It is approximately 1,050 km (650 mi) south of Beijing, 700 km (430 mi) west of Shanghai, and 900 km (560 mi) north of Hong Kong. Direct international flights from Wuhan connect it to major cities in Europe and North America.
In Wuhan, during December 2019, a cluster of cases displaying the symptoms of a "pneumonia of unknown cause" was linked to Huanan Seafood Wholesale Market, which had a thousand stalls selling fish, chickens, pheasants, bats, marmots, venomous snakes, spotted deer, and other wild animals (ye wei, bushmeat). In January 2020, the hypothesis was that this was a novel coronavirus from an animal source (a zoonosis). In February 2020, the Chinese authorities have confirmed a highly pathogenic strain of the H5N1 bird flu in chickens in the Hunan province.
Coronaviruses mainly circulate among other animals but have been known to evolve and cause coronavirus outbreaks in humans as in the cases of severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) together with four further coronaviruses that cause mild respiratory symptoms similar to the common cold. SARS-CoV-2's nucleic acid sequence is 75- to 80-percent identical to severe acute respiratory syndrome coronavirus (SARS-CoV), and more than 85-percent similar to several bat coronaviruses. All coronaviruses known to infect humans have been shown to spread between people. Transmission of coronaviruses is primarily thought to occur among close contacts via respiratory droplets generated by sneezing and coughing.