BEIJING, Jan. 30 (Xinhua) -- Better test capability and expanded test coverage are important reasons for the surge in the number of confirmed cases of novel coronavirus infections in China, experts have said.

Chinese health authorities announced Thursday that 7,711 confirmed cases of pneumonia caused by the coronavirus had been reported in 31 provincial-level regions and the Xinjiang Production and Construction Corps by the end of Wednesday. Wednesday saw 1,737 new confirmed cases and 4,148 new suspected cases.

In Wuhan of Hubei Province, the epicenter of the outbreak, over 12,000 new test kits have been issued to test institutions and designated hospitals, which has enabled the city to test nearly 2,000 suspected case samples in a single day, compared with only 200 samples at the early stage of the epidemic, said the municipal health commission Tuesday.

Tests can now be conducted in Hubei without having to send the samples to Beijing, according to Ma Guoqiang, Party secretary of Wuhan.

Li Xingwang, an infectious disease expert with Beijing Ditan Hospital and a member of China's national expert team against the coronavirus, said expanded test coverage has identified some infected cases without any symptoms.

The strong human-to-human transmissibility of the virus is also one of the reasons for the surge in confirmed cases.

Researchers have found that it only takes the novel coronavirus six to seven days to double the number of confirmed cases, compared with about nine days for the SARS virus, according to Feng Zijian, deputy director of the Chinese Center for Disease Control and Prevention.

The low number of discharged patients is due to the fact that patients must strictly meet the discharge standards set by the state before being released.

It generally takes about one week for patients with mild symptoms to recover, and two weeks or more for those with severe symptoms, Li said.

"With clinical symptoms basically relieved and their body temperatures returning to normal, cured patients need to go through two virus detections before being discharged to ensure no infectivity," he added.

Judging from the cases admitted so far, most patients have a favorable prognosis and children's symptoms are relatively mild.

There has been a recent increase in the number of mild cases, with some patients showing no symptoms of pneumonia, only mild fever or occasional dry cough, according to Li.

Infected people can spread the virus even if they show no symptoms or only have mild symptoms including mild fever, occasional dry cough or fatigue, Li said, adding that they may not be as contagious due to less coughing.