Health officials in the central province of Hubei reported 14,840 new cases of COVID-19 on Thursday, the largest single-day increase recorded so far and an almost tenfold jump from Wednesday.

The sudden surge — which officials and experts largely attribute to a shift in diagnostic criteria rather than a spike in newly symptomatic patients — has shaken hopes that the epidemic might be nearing its peak. It has also underscored how inaccurate testing kits and slow-moving confirmation protocols continue to hamper efforts to understand the true scale and spread of the ongoing novel coronavirus epidemic.

In an announcement early Thursday morning, Hubei’s provincial health commission stated that it would begin adding patients that had been clinically diagnosed — that is, diagnosed by a physician but without having had their illnesses confirmed via a nucleic acid test — to its daily tally of confirmed COVID-19 cases.

The move came eight days after the National Health Commission released guidelines permitting doctors in Hubei, but not elsewhere in China, to make clinical diagnoses of COVID-19 “when radiographic imaging of potential cases reveals features of pneumonia.” The commission’s guidelines also directed Hubei’s health authorities to treat clinically diagnosed cases as confirmed when releasing data to the public. It is unclear why the province waited a week before applying the new standards.

Generally speaking, a positive nucleic acid or genetic sequencing test result is required before health authorities will confirm the existence of a novel coronavirus infection. But the situation in Hubei has been complicated by a chronic shortage of test kits and a high rate of false negatives. Wang Chen, an expert in respiratory diseases at the Chinese Academy of Medical Sciences, told the country’s state broadcaster last week that nucleic acid tests given to those who “definitely” had the disease only came back positive 30% to 50% of the time.

Doctors on the ground have been calling for greater flexibility for weeks. On Feb. 3, the Hubei provincial authorities received a request that physicians be allowed to bypass the lengthy and unreliable nucleic acid testing process and diagnose cases on the basis of lung scans.

Experts, however, caution that diagnoses made on the basis of lung scans may not be reliable outside of the outbreak’s epicenter.

Lu Hongzhou, a virologist at Shanghai’s Huashan Hospital, told Sixth Tone that the relaxed diagnostic guidelines should only be applied in places where there is a high concentration of known infections.

“It’s the flu season, so many people with clinical symptoms similar to COVID-19 may just have the flu,” Lu said. “The likelihood of a patient in Hubei having COVID-19 instead of the flu is greater than in other places.”

Excluding Hubei, China’s health authorities reported 312 new cases of COVID-19 nationwide Thursday, down from 377 the previous day.

The vast majority of clinically diagnosed cases were reported in Hubei’s provincial capital of Wuhan, where the outbreak is believed to have originated last December. The city recorded more than 13,000 new cases Thursday, bringing its confirmed total to over 30,000.

There are signs the city may be hard-pressed to keep up if that number continues to rise. According to calculations from Sixth Tone’s sister publication The Paper, Wuhan has just 37,000 hospital beds. That number includes not only formal medical institutions, but also newly built temporary treatment facilities like Huoshenshan Hospital and makeshift clinics being set up in university dorms and recreational centers across the city.

Editor: Kilian O’Donnell.

(Header image: A medical worker talks to a patient at Jinyintan Hospital in Wuhan, Hubei province, Feb. 13, 2020. Yuan Zheng for Sixth Tone)