China’s decision to exclude individuals who carry the new coronavirus but show no symptoms from the country’s public tally of infections has drawn debate over whether this approach obscures the scope of the epidemic, with a document received by Caixin showing a significant proportion of one province’s cases show no symptoms.
Since early February, the National Health Commission (NHC) has concluded that “asymptomatic infected individuals” can infect others and demanded local authorities to report those cases. However, the commission has also decided not to include these people in its statistics for “confirmed cases” or indeed to release data on asymptomatic cases.
On Feb. 25, in Northeast China’s Heilongjiang province there were 104 asymptomatic infected individuals, according to a Feb. 26 Heilongjiang Provincial Center for Disease Control and Prevention document obtained by Caixin. That same day the province said (link in Chinese) it had 480 “confirmed cases,” a tally which did not include the 104 asymptomatic cases.
Known contagion risk
In its Jan. 28 virus prevention and control plan, the NHC demanded the prompt detection and reporting of those with light or no symptoms.
According to a document obtained by Caixin, the Heilongjiang CDC confirmed its first asymptomatic individual on Feb. 1 and asked the NHC for permission to leave the case off its public list of confirmed cases.
In a statement to Caixin, the Heilongjiang CDC said that it was told by the national CDC to “temporarily” include asymptomatic cases in public tallies with confirmed, symptomatic cases.
However, two days after the fourth edition of the NHC’s Covid-19 guidelines released on Feb. 7 said asymptomatic cases should be reported separately and excluded from the confirmed case tally, Heilongjiang removed 13 asymptomatic infected individuals from its tally of “confirmed cases.”
However, multiple studies from both Chinese and overseas researchers have been published, suggesting that individuals infected with Covid-19 can be contagious even if they do not feel ill.
In earlier guidelines, asymptomatic individuals were supposed to be observed and treated at home. But by the fifth edition of the NHC guidlines released Feb. 21, they had to undergo a 14-day quarantine as well as test negative in two separate nucleic acid tests before being released.
Health authorities have also developed criteria to determine whether an asymptomatic individual is the source of infection in any given cluster.
Nevertheless, at a Feb. 14 press conference, NHC deputy director Zeng Yixin said that the country would only publicize “suspected” and “confirmed cases.”
“If you don’t have symptoms, it’s not an illness,” he said. “There’s no need to announce it.”
In one instance where data on asymptomatic infected individuals was revealed, a study published Feb. 12 in the Chinese Journal of Epidemiology suggested that the group accounted for only 1.95% of all lab-confirmed infections. In contrast, this group made up 10.2% of total infections in Japan’s figures as of Wednesday, or 19 of 186 infections, excluding those from the Diamond Princess cruise ship in the port of Yokohama.
Making a case
In an interview with Nature last week, Wu Zunyou, China’s chief epidemiologist, defended the country’s treatment of asymptomatic data.
He told the magazine that a positive nucleic acid test – a genetic sequencing test used to detect the coronavirus – does not necessarily indicate an infection because viral genetic material detected through throat or nasal swabs does not confirm the virus has entered cells and begun to multiply. This notion was also echoed by Chinese representatives at the WHO.
But this view has been challenged by both domestic and overseas experts, who said that a virus must have replicated to reach detectable levels.
“If you aren’t considered sick if you don’t have symptoms, then what are you?” one expert that participated in the NHC’s revisions to its diagnosis and treatment criteria, who requested anonymity, told Caixin. “Is the nucleic acid test a gold standard or not?”
He added that as coronavirus action plans were revised, of whether or not to include asymptomatic individuals in the tally of confirmed cases was discussed, but ultimately rejected by the NHC. “Those that don’t appear sick make the best hosts for viruses,” he said.
According to Michael Mina, assistant professor of epidemiology and immunology at the Harvard School of Public Health, the existence of large quantities of asymptomatic individuals would lower the statistical rates of risk, such as of severe illness or death. Meanwhile, he said that China’s categorizations are understandable if used to allocate health resources, but providing epidemiologists around the world with accurate numbers for mitigation strategies would only require an additional column in data sets.
"Perhaps the most important component at this point is it shows that it may be even more widespread and difficult to contain than we think," Mina said. “I think any withholding of known figures pertaining to infections not only does a disservice to China’s ability to monitor and help control the epidemic but also inhibits global scientists from being able to learn from and disseminate useful information both back to China and to the global community.”
Contact reporter Dave Yin (davidyin@caixin.com) and editor Joshua Dummer (joshuadummer@caixin.com)
