China changed the way it accounts for coronavirus cases. The complete image is far from being finished.

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Patients describe what it is to get coronavirus 3:01

(CNN) - When China reported a drop in the number of new cases of the deadly coronavirus earlier this week, hopes were raised that the outbreak could be declining.

But on Thursday, health authorities in Hubei, the province at the center of the epidemic, announced that there were almost 15,000 new cases during the night, almost 10 times the number of cases announced the day before.

The government hastened to point out that the outbreak did not suddenly get worse; the authorities simply changed the way they reported the cases to allow more people to access the treatment faster.

“Our forecast was 1,500 new cases, and I opened my computer and there are 15,000 new cases. I think my hair got on end, ”said David Fisman, a professor of epidemiology at the University of Toronto, who has spent a lot of time modeling the current outbreak of coronavirus.

The change in how new cases are diagnosed has raised questions about whether the world can rely on the numbers that leave China, amid criticism about the government's handling of the outbreak.

How has China changed its method?

The total number of cases reported by China now includes "clinically diagnosed cases." These are patients who show all the symptoms of Covid-19 but have not been able to get tested or are believed to have false negative results.

Fisman said this was a positive move by the Chinese health authorities. "They should be applauded for that because they are expanding the network to try to do a better job to control the spread of people who do not yet have a firm diagnosis," he said.

If the sudden increase in numbers is disconcerting to some, it does not really mean an increase in the number of people who have fallen ill. In fact, Fisman said it would be "phenomenally irresponsible" to say that the epidemic worsened. "Case definitions change, that's a good public health practice, they don't want to miss cases," he said.

Delays in testing are not limited to China. In the United States, the Centers for Disease Control (CDC) currently requires that all potential samples be sent to their central laboratories for complete testing.

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Speaking at a hearing in the United States Senate on Wednesday, before China's announcement, Scott Gottlieb, former commissioner of the US Food and Drug Administration, urged a similar change in the procedure in the country to curb any potential outbreak He said the tests were not conducted aggressively enough and should be expanded to cover more symptoms.

“I think we should lean very aggressively to expand diagnostic screening at this time, particularly in communities where there is a lot of immigration, where these outbreaks could arise, to identify them in a timely manner so that they are small enough so that we can intervene to prevent further spread of the disease in this country, ”he said.

Should we be more skeptical about what China says?

The World Health Organization has supported China and the way it now reports the numbers. But many have expressed alarm at taking the figures to the letter, given the government's history of suppressing information about this and previous crises.

Since the beginning of the outbreak at the end of last year, Chinese authorities have tried to control the flow of information around the coronavirus. Li Wenliang, a doctor at the epicenter of the Wuhan outbreak, tried to raise the alarm about the virus from the beginning, but the police quickly rebuked him. Li himself died from the virus last week and his death has led to a level of public protest rarely seen in China.

Gottlieb, the former FDA commissioner, was one of those who publicly questioned the quality of data leaving China.

"I don't trust the reports in China, and I also believe that China's numbers reflect the most severe cases, so we are getting a biased view of the lethality rate and how serious it is," he said Wednesday.

Fisman said that while real numbers are likely to be somewhat higher than official numbers, most of the discrepancy probably involves minor cases.

"What I can say as someone who models infectious diseases, is that the numbers of virologically confirmed cases make sense to me," he said.

• MORE: The ABC of the coronavirus: what it is, how it is spread, who it affects and how it is prevented

However, some questions remain.

"In China, the party line is 'this started in December,'" Fisman said. “Those of us who are lucky enough to not have to repeat an official truth are able to say no, no, the phylogenetic data of the virus says that in early November, and epidemic models based on counts of exported cases, in which we trust, they show that it was from the beginning until the middle of November ”.

China's leaders have promised absolute transparency about the virus, and WHO has praised them for sharing information. Beijing has also promised severe punishment for any official who is hiding or minimizing the figures related to the outbreak.

Will we ever know the real number?

It can take years to get a real picture of an epidemic. Establishing the true scope of the SARS outbreak in 2002 and 2003 was a long-term process, partly because China suppressed its notification in the first months.

But even if the authorities do everything possible to reveal precise numbers, the entire image will not be finalized until much later.

Testing could also be a problem. Asha George, executive director of the Bipartisan Biodefense Commission, said at the same US Senate hearing on Wednesday that China may have limitations in its evidence and reporting resources, rather than simply "a lack of desire on the part of the Chinese government to report".

"We really won't know what the true lethality of this is until probably in a few months or years, when people do ... blood tests and find out how many silent infections there were in the population," Fisman revealed.

He added that, for the moment, health experts do not have a clear idea of ​​how many of the cases reported from China are occurring in health care centers and hospitals, where the mortality rate could be higher, because people who are in a Hospital for this or another reason are more vulnerable.

What does it mean for the world if we don't know the true number?

Of course, having accurate information is key to fighting an epidemic, because it helps epidemiologists predict the spread of the disease, which in turn allows public health officials to implement the necessary measures.

But although the number of reported cases plays a role, it is not the only way, and in some cases it is not even the most important when measuring an outbreak.

"We always measure large epidemics indirectly, usually using some different data sources, knowing that they will all be wrong in different places, but that the combined image is often very, very useful in terms of finding out what should be happening," Fisman said. .

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Most epidemiologists know what the obstacles are and can work with that, he said.

George told lawmakers that students in public health schools are often taught to "multiply by 7 or 8 times what they have said" to account for cases they cannot see.

"For every case you see, there are seven or eight out there that you don't see," he said.

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