The Chinese health authorities have ruled out severe acute respiratory syndrome (Sars) as the source of the mystery Wuhan virus, as the number of infected people continues to climb.
Some 59 people in the central Chinese city have come down with what the authorities are calling a "pneumonia of unknown cause", according to official figures released on Sunday night. It is higher than the 44 reported last Friday.
The city's health authorities have also ruled out bird flu, influenza, adenovirus and the Middle East respiratory syndrome coronavirus, or Mers-cov, as the cause.
But the Wuhan Municipal Health Commission also said in its update that the number of people in critical condition has dropped to seven from 11 previously, adding that all patients are in quarantine and in a stable condition.
Many of the patients are sellers from a local seafood wholesale market in the city. All of those affected had fallen ill between Dec 12 and 29.
Besides seafood, the market is known to also sell live animals, including birds and snakes, and the organs of rabbits and other wildlife, according to media reports.
Wuhan, the capital of central Hubei province, is a city of more than 11 million people.
The Chinese health authorities are racing to identify the mystery virus and its source.
A total of 163 people who had close contact with those affected have been put under observation, and the Chinese authorities are searching for more who had close contact with those infected.
Number of people, who had close contact with those affected, put under observation.
The World Health Organisation (WHO) said in a statement that based on the preliminary information from the Chinese investigation team, "no evidence of significant human-to-human transmission and no healthcare worker infections have been reported".
However, it added that the fact the cases are linked to a wholesale market could indicate an "exposure link to animals".
"In addition to treating the patients in care and isolating new cases as they may be identified, public health officials remain focused on continued contact tracing, conducting environmental assessments at the seafood market, and investigations to identify the pathogen causing the outbreak," the WHO said in a statement. It added that it is closely monitoring the situation and is in close contact with the Chinese health authorities.
The outbreak has triggered heightened checks on travellers from Wuhan across Asia, including in Hong Kong, Singapore and the Philippines, as cities take precautions against the spread of infection.
In Hong Kong, 17 people have been admitted to hospitals there so far, with eight confirmed not to have the virus.
Meanwhile, a three-year-old girl with a history of travel to Wuhan who was hospitalised in Singapore with pneumonia and suspected to be infected with the mystery virus turned out to have respiratory syncytial virus.
The virus, a common cause of childhood pneumonia, is not linked to the Wuhan pneumonia cases, Singapore's Ministry of Health said on Sunday.
The mystery Wuhan virus has raised the spectre of the deadly, flu-like Sars virus, which originated in China and killed more than 700 people around the world in 2002 and 2003.
Beijing's handling of Sars then was heavily criticised - when it initially sought to cover up the epidemic, a move which experts said led to more deaths.
Netizens initially blamed Sars as the source of the latest out-break - prompting police in Wuhan to arrest eight people for spreading rumours.
Communicable diseases expert Yang Gonghuan said the country's experience with Sars had led many Chinese to think the pneumonia from Wuhan is a repeat of that pandemic from the noughties.
Sars is suspected to have originated in bats and later infected humans, where it evolved the ability to be transmitted between people.
This process of evolution can happen "quite rapidly" in viruses, said Dr Yang.
Media reports on the mainland have been scant, as the authorities try to downplay the outbreak. But questions remain about whether there are unreported cases in other parts of China.
Dr Yang said reporting standards of infectious diseases in China have improved greatly from the Sars period, when the authorities engaged in cover-ups, and reporting methods were backward and primitive.
"While there is a system in place, some areas might not be as proactive in reporting cases, but the country is so big, I fear this might be unavoidable," she said.