Explanation: China’s symptom-free coronavirus carriers raise fears of a new wave of infections

SHANGHAI (Reuters) – The existence of a significant but unknown number of asymptomatic carriers of the coronavirus in China has raised public concerns that people could still spread COVID-19 without knowing that they were sick.

As the virus continues to wreak havoc worldwide, China is on the verge of victory and is already loosening travel restrictions. The border of Hubei Province, the epicenter of the virus, was opened on Wednesday after a two-month shutdown.

However, there are concerns that the end of the ban will put thousands of infectious people back on the market.

Asymptomatic cases pose a major challenge in controlling infectious diseases and make it difficult to recognize and stop the transmission.

In China, the number of known asymptomatic cases is classified and not included in the official data, although the South China Morning Post recently, citing unpublished official documents, said it was more than 40,000.

China had reported 81,218 coronavirus cases and 3,281 deaths by the end of Tuesday.

Asymptomatic cases are currently found through “contact tracking”. China identifies people who are exposed to a person with a confirmed diagnosis. If tested positive, they will be quarantined regardless of whether they show symptoms or not.

“Asymptomatic patients were all discovered during our contact tracking,” said Wu Zunyou of the Chinese Center for Disease Control and Prevention at a briefing on Tuesday. “So will they be able to do a broadcast? You will not do it. ”

However, the failure to include it in the official data has raised concerns about Beijing’s commitment to transparency, and some experts say that this could also create a misleading picture of how the epidemic is spreading and whether it is under control or not.

Although there were no new infections from March 18-22, the COVID-19 hotspot city of Wuhan announced on March 20 that a newly diagnosed case was not included in the official data since the patient, a 62-year-old Man with the last name Zhang, shown this had no symptoms.

Citing hospital sources, news magazine Caixin also reported that a new case in Wuhan on Tuesday was a doctor infected with an asymptomatic patient.

According to China, asymptomatic patients are included in the list of confirmed patients if they later show symptoms. However, it remains unclear how many asymptomatic cases are not diagnosed and therefore are not quarantined.

Some experts warn that undetected, asymptomatic patients could create new transmission routes as soon as the blockage is relaxed.

“It is particularly worrying that sufficient community testing is not yet required in many countries,” said Adam Kamradt-Scott, a public health specialist at the University of Sydney.

It is also unclear how much they could infect others.

“We know this is possible, but we don’t think it is a key driver of transmission,” said Maria Van Kerkhove of the World Health Organization at a briefing in early March.

New studies show that asymptomatic carriers can pose risks. An analysis of the Diamond Princess cruise ship outbreak found that 33 of the 104 infected passengers remained asymptomatic even after an average of 10 days of observation at the Central Self-Defense Force hospital in Japan.

While many looked healthy throughout, some other passengers who were initially asymptomatic quickly became seriously ill.

Passengers wearing face masks to prevent the spread of coronavirus disease (COVID-19) are seen on a Shanghai Airlines plane at Shanghai Hongqiao International Airport in Shanghai, China, on March 25, 2020. REUTERS / Aly Song

Another study published on March 23 that examined cases in the southwestern city of Chongqing found that 18% of the patients were asymptomatic. Another even found that people are more likely to transmit the disease when the symptoms are mild.

The Yale School of Public Health said that the presence of presymptomatic (asymptomatic) patients meant that screening procedures at airports and other entry points were not sufficient to prevent the coronavirus from spreading from China to other countries.

“The real picture only becomes apparent when we have a serological test to find out who got the infection,” said Ian Henderson, director of the Institute of Molecular Biosciences at Queensland University.

Additional reporting by the Shanghai Newsroom and Sophie Yu in Beijing; Edited by Michael Perry

Our standards:The Thomson Reuters Trust Principles.

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