Coronavirus Testing in China Finds More Symptom-Free Cases

Almost four out of five people who were tested positive for coronavirus in China this week showed no signs of Covid-19.

(Bloomberg) -- Two out of three people who tested positive for coronavirus in China this month had no typical signs of Covid-19, highlighting the challenge of identifying infections and stopping its spread.

Of 181 new infections detected, 115 -- or 64% -- didn’t have a fever, cough or other symptoms used to identify probable cases, according to China’s National Health Commission. The testing was conducted in the 48 hours through midnight Thursday. The agency has 1,027 so-called asymptomatic people under medical observation, 221 of whom have traveled from other countries, it said Friday.

With the pandemic-causing virus infecting more than 1 million people across the world, scientists are finding a wider range of manifestations than previously recognized. These include an abrupt loss of smell and taste, to unusual neurological symptoms in a small number of cases, said Mady Hornig, a physician-scientist at Columbia University’s Mailman School of Public Health in New York.

Coronavirus Testing in China Finds More Symptom-Free Cases

“We’re trying to fit all these pieces together to know what is Covid-19?” she said in a phone interview. “When you first have an outbreak or any disease, and if it hasn’t been identified before, you have a process of creating a case definition.”

That process may ultimately lead to identifying additional features of the disease that weren’t initially apparent, said Hornig, who is also an associate professor of epidemiology.

Recognition of a broader spectrum of disease may mean more people may need to be tested to identify cases with atypical symptoms. To prevent further spread, the World Health Organization recommends infected people be isolated and those with whom they have been in contact traced to find other potential cases.

Asymptomatic Cases

Asymptomatic cases are defined as individuals who test positive for the coronavirus without displaying symptoms such as fever, cough and sore throat that’s self-noticeable or discernible clinically, the National Health Commission said on March 31. Some of those cases will develop symptoms over a 14-day incubation period; others will remain symptom-free.

The U.S. Centers for Disease Control and Prevention recently revised its public health recommendations for managing the pandemic, recognizing that even people who appear healthy may spread the disease. Infected people may risk spreading the infection 48 hours before their symptoms appear, the CDC said.

The possibility of so-called presymptomatic transmission of the novel coronavirus, officially known as SARS-CoV-2, poses challenges for disease control, researchers in Singapore said Wednesday. They reported seven clusters of cases in which the disease probably spread that way.

Silent Carriers

Widespread testing in countries including Iceland and South Korea have also identified a high proportion of infections in people without discernible symptoms, stoking concern that the number of silent carriers may be greater than previously thought.

Hubei, the central Chinese province where the pandemic emerged at the end of 2019, reported 51 asymptomatic cases on April 2 -- the majority of the national total for that day.

The data raise questions over whether the outbreak there is truly contained. The official national daily case tally has dwindled to fewer than 100, after spiking to the thousands in mid-February. Following criticism of its data collection, China started publicizing the number of confirmed symptom-less cases this week.

The possibility of symptom-less transmission “increases the challenges of Covid-19 containment measures, which are predicated on early detection and isolation of symptomatic persons,” Vernon J. Lee and colleagues at Singapore’s Ministry of Health wrote in their report.

“The magnitude of this impact is dependent upon the extent and duration of transmissibility while a patient is presymptomatic, which, to date, have not been clearly established,” Lee said.

Virus Flare-Up

There is some complexity around which cases truly have no clinical signs and which ones have very mild symptoms, according to researchers in South Korea, who pointed to the example of the outbreak on the Diamond Princess cruise ship.

About half of the 619 confirmed cases were asymptomatic at the time of diagnosis, some of whom showed “objective clinical abnormalities,” they said.

A study of 24 people in Nanjing, in China’s Jiangsu Province, who tested positive without any usual symptoms cases found five patients developed fever, cough and others symptoms during hospitalization. The research, published in March, found 12, or half of the cases, had signs of Covid-19 based on chest CT scans. Only seven, or 29% of cases had a normal CT image and had no symptoms during hospitalization.

A county in central China was put back under lockdown this week after a flare-up in cases. A woman in Jia county was infected after she visited a doctor who had the coronavirus but showed no signs of being sick.

©2020 Bloomberg L.P.