Around the world, if someone tests positive for COVID-19, it is a confirmed case. But that is not always how it works in China.
Official documents show that China does not count asymptomatic carriers of the virus in its tally of confirmed cases. That practice is not consistent with the World Health Organization's guidance, and it skews the Chinese data that epidemiologists have relied on to model how the virus spreads.
Changing definitions for who is infected
China publicly changed the criteria for tracking infections a few times early on in the outbreak.
In January, when the infections started surging exponentially, China's Health Commission decided that people without symptoms should not be included in the confirmed case count.
In the "Pneumonia Case Surveillance Program for New Coronavirus (Third Edition)" released by the commission on January 28, health officials outlined three categories of coronavirus cases: suspected cases, confirmed cases and positive diagnosis. Those classified with a positive diagnosis are not included in the country’s tally of infected people.
A copy of the guidelines that VOA found on the commission’s website states, "Among those diagnosed as 'mild cases' and 'Asymptomatic infection,' uniformly select the 'Positive Diagnosis' category.”
The day after the third edition was published, the National Health Commission subtracted more than 100 cases from the national count.
The criteria for positive patients have been updated several times since then, but the classification of confirmed cases has been kept basically the same.
The sixth edition of the guidelines, released March 7, reads (emphasis added), "Asymptomatic patients with clinical manifestations will be promptly amended as confirmed cases."
This approach puts China at odds with the WHO’s guidance. The Chinese version of the WHO's guidelines reads: "The confirmed cases are those diagnosed with COVID-19 virus in the laboratory with or without clinical signs and symptoms."
Dr. Huang Yanzhong, a senior fellow for global health at the Council on Foreign Relations, told VOA that he has not heard of any other governments that use the same criteria for confirmed cases as China. "In other countries, asymptomatic carriers are indeed counted into confirmed cases as long as they test positive," Huang said.
The Wuhan case
March 19 was supposed to mark a milestone for China in its fight against the virus. On that day, no new locally transmitted cases were reported across the country for the first time since the pandemic began. But a public notice posted by local authorities outside a Wuhan community said there was a new confirmed case inside the residential compound.
A photo of the notice went viral on social media. People asked why this case was not being recognized in Beijing’s official count. For critics who have long questioned Beijing's figures, the reported Wuhan infection was further evidence that national authorities are minimizing the scope of the outbreak.
Tao Zhengtai, a local party secretary, later confirmed that the announcement was indeed posted by the community authority. But he told the official Xinhua news agency last Sunday that it was a mistake. He said a 63-year old man surnamed Zhang in Wuhan's Qiaokou district tested positive but had shown no symptoms. "Mr. Zhang is asymptomatic, not a confirmed case," Tao said.
The Qiaokou District Disease Control Command that posted the announcement also issued a statement saying that according to the sixth edition of the guidelines issued by the National Health Commission, even if Zhang's nucleic acid test result was positive, “his case should not be classified a confirmed case.”
“Until March 19, we didn't know that asymptomatic patients were not counted as confirmed cases,” the CFR’s Dr. Huang said in a telephone interview with VOA on Thursday. "We didn't realize that there was such a discrepancy in China's tally."
Beijing downplays transmission risk
The number of known asymptomatic cases is classified information in China. Citing unpublished official documents, a recent report by South China Morning Post said that asymptomatic patients, or “silent carriers,” could constitute as much as one-third of those who test positive.
What also remains unclear is how many asymptomatic cases remain undiagnosed. A paper by researchers at the Huazhong University of Science and Technology, published March 20 on the website of i, a top scientific journal, estimated that asymptomatic cases could represent 30 percent to 60 percent of all infections.
While admitting that asymptomatic infections are a potential cause for concern and for transmission, China maintains those cases are not a problem. It emphasized that silent carriers are held in centralized quarantine for 14 days and observed to see if they become symptomatic.
Liu Jiafa, the party chief of Hubei Provincial Center for Disease Control and Prevention, assured the public Friday that it would not release asymptomatic carriers who are quarantined unless two consecutive samples of negative nucleic acid tests are negative.
"The public need not worry too much," Liu said.
Besides assurances, China has not offered an explanation as to why it keeps the count of asymptomatic carriers, but the numbers are not included in the official public data.
"It is odd that they are not counted in the officially reported confirmed cases in China," the CFR’s Huang, who also directs the Global Health Governance roundtable series, said. "If the result of nucleic acid test is positive, that is a confirmed case. Period."