China Focus: Four things you should know about silent coronavirus carriers

Here are four important things you need to know about asymptomatic coronavirus carriers.

WUHAN, April 13 (Xinhua) — Though China has seen its domestically transmitted cases of novel coronavirus (COVID-19) maintain low levels thanks to stringent epidemic prevention and control measures, imported cases and asymptomatic carriers have become the major concern among the public who fear a possible second wave of infection.

The latest figures from the National Health Commission on Sunday showed 61 new asymptomatic cases, including 12 from abroad, were reported on the mainland. A total of 28 asymptomatic cases, all imported, were re-categorized as confirmed cases, and 1,064 asymptomatic cases were still under medical observation by Sunday.

Here are four important things that can give you a better understanding of asymptomatic coronavirus carriers.

1. HOW CONTAGIOUS IS IT?

“The infectivity of asymptomatic carriers depends on different situations. If such cases are found after a long period of isolation in Wuhan, the infectivity is very low. If an asymptomatic coronavirus carrier is found among returnees from places where the epidemic is still serious, the infectivity would be quite high,” said Wei Sheng, a professor at the School of Public Health of Tongji Medical College of Huazhong University of Science and Technology.

According to Tong Zhaohui, vice president of the Beijing Chao-Yang Hospital, there are two types of asymptomatic infections. “One is pre-symptomatic — referring to patients that have not yet developed any symptoms but are actually in incubation period. These people need to be screened out and managed as confirmed cases. The other are people who show neither any symptom nor pathological changes in CT scan imaging. They are the real asymptomatic carriers. They are not patients but just test positive for nucleic acid,” said Tong.

An analysis, conducted by the National Health Commission, of silent coronavirus carriers reported between Jan. 29 and April 8 on the Chinese mainland showed that the proportion of silent carriers developing into confirmed cases was declining. The ratio remained below 11.2 percent after March 10, and in some places it was even lower than 6 percent.

“Asymptomatic carriers do have certain infectivity but it’s generally weak, and much lower than that of symptomatic infected persons,” said Tong. “Droplets containing the virus cannot shed without sneezing, coughing or other symptoms, so silent carriers are less likely to infect others.”

“Most Wuhan residents have been quarantined for more than 70 days. The likelihood of infection is minimal from Wuhan people with green health codes — which indicate that they’re healthy,” said Wei.

2. WILL ASYMPTOMATIC INFECTIONS CAUSE A REBOUND IN EPIDEMIC?

Bans on outbound traffic were officially lifted after 76 days in Wuhan, the former epicenter of COVID-19 in China, on April 8, and attention has hence been focused on the risk of cross infection at workplaces.

“Asymptomatic infection is not a special product of COVID-19. All infectious diseases such as measle, influenza and SARS have a certain proportion of asymptomatic infections, and silent carriers in none of the cases had caused a large-scale outbreak in society,” said Tong.

Tong noted that preliminary epidemiological investigation into SARS and COVID-19 both proved that asymptomatic carriers have very limited infectivity and will not cause large-scale transmission. He added that the risks can be well controlled as long as the epidemic prevention and control measures are fully implemented.

Li Qun, director of the Health Emergency Center of the Chinese Center for Disease Control and Prevention, said that preparations have been made to resume work and production in order to cope with the possible transmission risks brought about by the increase of personnel mobility.

“Once an asymptomatic carrier is found, isolated observation and detailed epidemiological investigation shall be carried out in a timely manner, and control and monitoring shall be strengthened in key areas and among close contacts. We hope these measures can help trace more asymptomatic carriers and reduce the chance of transmission,” said Li.

“Currently all sides have attached great importance to the prevention and control of asymptomatic carriers. So people do not need to worry too much,” Li added.

3. HOW TO SCREEN AND MANAGE ASYMPTOMATIC CARRIERS?

There are mainly four sources of asymptomatic carriers found in Wuhan — close contacts of confirmed patients, ordinary outpatients, employees screened before resuming work, as well as those screened before leaving Wuhan.

A new asymptomatic case will be reported within two hours to local centers for disease control and prevention and a case investigation should be completed within 24 hours, according to Li.

“Asymptomatic carriers are applied with the same quarantine and medical observation measures as confirmed cases,” said Li, who added that asymptomatic carriers should be put under centralized medical observation for 14 days, and will be immediately transfered to designated hospitals for treatment if they develop any symptom and be counted as confirmed cases.

“They must test negative for nucleic acid twice after the medical observation and be given a two-week follow-up visit. Their close contacts should also be put under a fortnight centralized medical observation,” said Li.

4. WHAT CAN WE DO WHEN THERE ARE SYMPTOMATIC CARRIERS?

Most asymptomatic carriers were found from close contacts of confirmed patients. “So people who have not been exposed to COVID-19 patients are not likely to be infected and there is no need to panic,” said Tong.

“The most important thing is to take proper protective measures,” said Li.

There is no need for those who have neither suspected symptoms nor close contacts with confirmed COVID-19 patients to take nucleic acid tests, according to experts, who added that good hygiene habits should be kept even after the epidemic.

“We should stay alert and avoid some subconscious behaviors like rubbing eyes after touching the mask,” said Li.