After a day in which infection numbers spiked because of a new method of tabulating cases, doctors say the change in approach will allow China to manage the coronavirus outbreak better.
Infection numbers reported on Thursday showed a jump of nearly 16,000 cases across China. There were 14,840 in the epicentre of Hubei province, with more than 13,000 counted using the new guidelines.
Scientists feared this could represent the tip of an iceberg, with the true scale of the spread vastly under-reported, but health officials said the startling increase was due to retroactively tabulated cases.
"Crucially, we understand that most of these cases relate to a period going back over days and weeks and are retrospectively reported as cases, sometimes back to the beginning of the outbreak itself," said head of the World Health Organisation's (WHO) health emergencies programme Mike Ryan.
"We have seen this spike in the number of cases reported in China, but this does not represent a significant change in the trajectory of the outbreak," he told a news conference at the WHO headquarters in Geneva.
China's National Health Commission yesterday reported an increase of 5,093 infections on Thursday - 3,095 in Hubei were diagnosed through the "clinical methods" of the new guidelines.
Beginning on Wednesday, Hubei province said that a "clinical confirmation" would suffice, meaning that a patient with symptoms who either had a history of contact with confirmed cases or a positive computed tomography scan showing signs of pneumonia could now be considered a confirmed case without a lab test. Known as "probable cases" in epidemic terminology, they are used by scientists to track the scale of an outbreak.
Under the previous methodology, cases could be confirmed only through a positive laboratory test, in line with WHO guidelines.
But healthcare workers have complained of a lack of test kits in Hubei, where samples can sometimes take up to two days to be confirmed, and where there was a shortage of medical staff. Infectious disease specialists have also said this means the number of confirmed cases in a day were limited by a laboratory's capabilities.
"Experienced doctors all know that loopholes exist in nucleic acid testing," a radiologist at one of Wuhan's top hospitals, who asked not to be identified, told Caixin magazine. Such "false negatives" can be caused by tests that may not be sensitive, issues with handling samples and even the quality of them.
It is also unclear why Hubei province took a week before it implemented the new criteria, though doctors have said the new counting method allows for China to better manage the disease's spread.
Overcrowded hospitals previously meant that patients who were not seriously ill or confirmed cases were sent home to await their results, potentially spreading the virus within their communities.
Professor Benjamin Cowling, an epidemiologist at Hong Kong University's School of Public Health, said this method of diagnosis "makes a lot more sense".
"We have always known that there are more coronavirus infections than indicated by the number of confirmed cases, partly because not everyone who has got pneumonia has been tested, and partly because many people with the coronavirus infection don't have pneumonia and are not eligible to be tested, and are not even eligible to be considered for testing in general," he said.