Coronavirus: Numbers dip sharply as China now excludes positive cases with no symptoms from confirmed tally
China is seeing a sharp decline in the number of confirmed coronavirus disease or COVID-19 cases since Wednesday. While the Chinese government has been calling this a success, other scientists have expressed doubts.
The drop can be attributed to a change in how the country is now confirming an infected person, say experts. This changed definition excludes those who show no symptoms -- even after testing positive for the disease.
Scientists are unhappy with this because it could mask the scale of the outbreak. “I’m very suspicious about anything they’re saying,” coronavirus expert Ralph Baric, from the University of North Carolina, told STAT, pointing to the low numbers China is reporting from other provinces in the country.
In China's defense, health authorities believe this measure could help them take care of sick patients who are spreading the disease. “The downward trend will not be reversed,” insisted Ding Xiangyang, deputy chief secretary of the State Council and a member of the central government’s supervision group.
This changed criteria -- introduced on Wednesday -- meant that the very confirmed cases have been surfacing in the country. From Tuesday's report of 1,749 new cases, the number of confirmed cases had dramatically dropped to 394 the next day. Since then, the numbers have remained below 1,000. According to the latest numbers released by China's National Health Commission on Friday, there were 889 new cases of confirmed COVID-19 and 118 deaths in China.
China's changing criteria
This is not the first time China has changed how it reports confirmed cases. Just last week, China began counting people who showed positive lung scans or CT scans, leading to a surge in the number of cases. The country diagnosed over 14,840 new infections -- all in a single day.
While the CT does not detect the virus, the nucleic acid test is more definitive. The nucleic acid test, which was used earlier, detects the virus in the throat or nose swabs collected from patients. But only using CT scans meant that doctors were also including suspected patients in the confirmed list.
The change confused even then. "It [the CT scan] is a non-specific method and is aimed at diagnosing people who have pneumonia," Dr. William Schaffner, Professor at the Vanderbilt University School of Medicine, Nashville, Tennessee, told MEA WorldWide (MEAWW).
Now, with the new guidelines, people who test positive but show no symptoms are called ‘positive cases’ rather than ‘confirmed cases’. If people in the positive category show signs of the disease, they will be moved to the confirmed category. For now, only confirmed cases are posted on China's National Health Commission’s official website.
Doubts and concerns
According to Wu Zunyou, the chief epidemiologist at the Chinese Center for Disease Control and Prevention in Beijing, some people harboring the virus in their throat and nose may not have the virus entering and infecting other parts of the body -- which may explain why these people show no symptoms.
But it is not clear whether such ‘carriers’ -- who test positive for the virus but are not infected -- exist. “That is one of the big scientific questions,” he told Nature.
Others see this scenario as unlikely. A virus usually has to infect and replicate inside a host to reach detectable levels, Angela Rasmussen, a virologist at Columbia University in New York, told Nature. If the virus is in a person’s nose but has not infected any cells, then “I’m skeptical that virus in a nasal swab from this type of exposure would be detectable,” she added.
Besides, this change in disease definition should have increased the number of suspected cases -- but it did not, according to Caitlin Rivers, an assistant professor of epidemiology at the Johns Hopkins Center for Health Security, who called the situation confusing.
This also makes it hard for scientists who try to make sense of how the virus spreads. For this, they might only need information on people who are infected but have no symptoms.
“I think between the inability to determine the actual number of people infected and how cases are now being called a case means at best you can get trend data, possibly, but not more than that, Michael Osterholm, director of the University of Minnesota’s Center for Infectious Diseases Research and Policy, told STAT.
However, some experts believe that China is probably also prioritizing care for the sick, and maintaining quarantines, rather than measuring the epidemic’s dynamics. “If I put on my medical hat for a moment, I can understand the decision not to count these individuals,” Michael Mina, an infectious-disease immunologist, and epidemiologist at the Harvard T. H. Chan School of Public Health in Boston, Massachusetts, said.