BEIJING (NYTIMES, REUTERS) - Chinese scientists refused to share raw data that might bring the world closer to understanding the origins of the coronavirus pandemic, independent investigators for the World Health Organisation (WHO) said Friday (Feb 12).

The team had requested raw patient data on the 174 cases of Covid-19 that China had identified from the early phase of the outbreak in December 2019 in the Chinese city of Wuhan, as well as other cases, but were only provided with a summary, said Dominic Dwyer, an Australian infectious diseases expert who is a member of the team.

Such raw data is known as "line listings", he said, and would typically be anonymised but contain details such as what questions were asked of individual patients, their responses and how their responses were analysed.

"That's standard practice for an outbreak investigation," he told Reuters on Saturday via video call from Sydney, where he is currently undergoing quarantine.

He said that gaining access to the raw data was especially important since only half of the 174 cases had exposure to the Huanan market, the now-shuttered wholesale seafood centre in Wuhan where the virus was initially detected.

"That's why we've persisted to ask for that," he said. "Why that doesn't happen, I couldn't comment. Whether it's political or time or it's difficult ... But whether there are any other reasons why the data isn't available, I don't know. One would only speculate."

The investigators, who recently returned from a fact-finding trip to Wuhan, also said disagreements over patient records and other issues were so tense that they sometimes erupted into shouts among the typically mild-mannered scientists on both sides.

China's continued resistance to revealing information about the early days of the coronavirus outbreak, the scientists say, makes it difficult for them to uncover important clues that could help stop future outbreaks of such dangerous diseases.

"If you are data focused, and if you are a professional," said Dr Thea Kolsen Fischer, a Danish epidemiologist on the team, then obtaining data is "like for a clinical doctor looking at the patient and seeing them by your own eyes."

For 27 days in January and February, the team of 14 experts for the WHO led the mission to trace the origins of the pandemic. Several say their Chinese counterparts were frustrated by the team's persistent questioning and demands for data.

Chinese officials urged the WHO team to embrace the government's narrative about the source of the virus, including the unproven notion that it might have spread to China from abroad, according to several members of the team. The WHO scientists responded that they would refrain from making judgments without data.

"It was my take on the entire mission that it was highly geopolitical," Dr Fischer said. "Everybody knows how much pressure there is on China to be open to an investigation and also how much blame there might be associated with this."

In the end, the WHO experts sought compromise, praising the Chinese government's transparency, but pushing for more research about the early days of the outbreak in Wuhan in late 2019.

It remains unclear if the compromise will work. The WHO scientists said they were continuing to press their counterparts in China for the raw data and other information.

The team members considered the trip, which ended this week, as a win mostly because they feel there is enough goodwill that talks and studies will continue. But they acknowledged there is too little information so far to answer critical questions.

And they were criticised already for handing the Chinese side a public relations victory at a closing news conference by endorsing the contentious idea that the virus might have spread by frozen food products.

On the crucial question of when the outbreak started, the team said it had not turned up evidence yet that it was earlier than China has reported. But the team was stymied at times by the lack of detailed patient records both from early confirmed cases, and possible ones before that.

"We asked for that on a number of occasions and they gave us some of that, but not necessarily enough to do the sorts of analyses you would do," said Dr Dominic Dwyer, an Australian microbiologist on the WHO team, referring to the confirmed cases.

The Chinese scientists also acknowledged they had discovered that 92 people were hospitalized in Wuhan as early as October 2019 with symptoms such as fever and coughing. The Chinese experts said they had found no trace of Covid-19 in those people, but the tests were incomplete. The WHO team members said more research was needed.

Any indication that the outbreak started earlier than December 2019 would leave China open to more criticism; Chinese officials have been widely criticised for initially trying to cover up the outbreak, and acting too late to stop it from spilling over into the rest of the world.

The WHO team, which is expected to release a full report about its findings in coming weeks, is still pressing Chinese officials to conduct exhaustive checks of blood samples for signs that the virus might have been circulating earlier. The experts are also asking China to more deeply investigate the wildlife trade in Wuhan and the surrounding area for clues about how the virus might have jumped from animals to humans.

It is unclear how fully the Chinese government - which remains in firm control of research into the origins of the virus - will cooperate.

When the experts arrived in Wuhan last month, they set out to find the earliest known cases of Covid-19, asking Chinese officials to examine records for patients who had been hospitalised with symptoms such as fever and cough as early as October 2019.

Chinese scientists, after a review of 76,000 records at 233 medical institutions in Wuhan, told the WHO team that they had found 92 individuals who fit that description. The government performed antibody tests on two-thirds of those people and reported that they were not positive for Covid-19. (The other third either died or declined to be tested, the Chinese scientists said.)

The WHO scientists were frustrated by the Chinese government's reluctance to explain how they had gathered the data, according to interviews with team members.

Dr Fischer said she would have expected to find many more cases of individuals who were hospitalised with such symptoms in a city the size of Wuhan.

In heated discussions, Dr Fischer recounted, the WHO experts urged the Chinese scientists to conduct a more thorough search. The team also expressed concerns about the reliability of antibody tests administered so long after the infections. Testing any original nose or throat swabs would be useful, but Dr Dwyer said there were none.

Chinese officials agreed to look more broadly at samples in Wuhan blood banks in 2019, though they said that they had not yet obtained permission to do so.

The WHO experts ultimately concluded that there was no evidence yet that the virus was transmitting on a wide scale in China before December 2019, but that more research definitely was needed.

Chinese commentators have seized on that finding to build on the government's mantra that it was possible that China was not the source of the outbreak, and to urge the WHO to look elsewhere.

The WHO team said it would look, but that they were skeptical.

"I think it started in China," Dr Dwyer said after the trip. "There is some evidence of circulation outside China, but it's actually pretty light."

During the visit, Chinese scientists also urged the WHO team to consider the frozen food theory that has gained traction in the country.

The WHO team ultimately agreed to explore in more detail how the virus might spread through frozen food. But in interviews, team members said the focus for now would be on frozen wildlife products sold in China - not imported food.