FAQs on asymptomatic infections of COVID-19

Starting April 1, the information of the asymptomatic infected persons will be included in the daily COVID-19 updates. How to define asymptomatic infected persons of COVID-19? Can asymptomatic infected persons spread the disease? What measures will be taken to strengthen the prevention and control of asymptomatic infections? The answers can be found in FAQs on the Prevention and Control of the Spread of COVID-19 Caused by Asymptomatic Infected Persons released by the National Health Commission.

1. How to define asymptomatic infected persons of COVID-19?

Asymptomatic infected persons of COVID-19 (hereinafter referred to as asymptomatic infected persons) refer to those who do not show any relevant clinical symptoms, such as fever, cough, sore throat and other self-perceived or clinically recognizable symptoms, but whose respiratory tract specimens test positive for COVID-19. Asymptomatic infected persons can be divided into two categories: 

One is that infected persons who test positive in the nucleic acid test do not show any self-perceived or clinically recognizable symptoms after the 14-day observation of the incubation period and the infection has been asymptomatic. 

The other is that infected persons who test positive in the nucleic acid test do not show any self-perceived or clinically recognizable symptoms when sampling, but later develop some clinical symptoms. That is "asymptomatic infection" during the incubation period.

2. Can asymptomatic infected persons spread the disease?

According to the monitoring data released by the State and some provinces, some asymptomatic infected persons have caused second-generation transmission among their close contacts, and they have set off a small number of clusters of infections according to epidemiological investigations. 

Studies with small sample sizes have shown that the viral loads in the respiratory samples of asymptomatic cases do not demonstrate distinct difference from those of confirmed cases. According to the current monitoring data and research, asymptomatic infected persons are contagious, but the length of the contagion period, the strength and pathway of transmission need to be further studied. 

Some experts believe that the risk of spreading the virus caused by asymptomatic infected persons is relatively lower than that by confirmed patients because asymptomatic infected persons show no clinical symptoms such as cough and sneezing though the pathogenic nucleic acid can be found in their respiratory tract specimens. 

3. What are the requirements for the prevention and control of asymptomatic COVID-19 infections in China? 

Protocol for Prevention and Control of COVID-19 (Edition 3) released by the National Health Commission on January 28 included asymptomatic infected persons into the prevention and control management scope. In the subsequent revision process, the report and management requirements of asymptomatic infected persons have been clearly specified by the National Health Commission. 

Medical and health institutions at all levels and of all kinds shall report asymptomatic infected persons they have identified directly through online platforms within two hours. Upon receiving the report of asymptomatic infected persons, CDCs at the county (district) level shall complete the case investigation within 24 hours and have the people in close contact with asymptomatic infected persons registered in time. 

The case investigation form or investigation report shall be timely reported through the report and management information system for infectious diseases. Asymptomatic infected persons shall be collectively quarantined for 14 days. In principle, the quarantine can be lifted for those who have been quarantined for 14 days and tested negative for nucleic acid tests in two consecutive samples (the minimum interval of sampling time shall be at least 24 hours). If the result of the nucleic acid test is still positive, the quarantine shall be continued. Asymptomatic infected persons shall be defined as confirmed COVID-19 cases in time for standard treatment if they show clinical symptoms during the quarantine. People in close contact with asymptomatic infected persons shall also be collectively quarantined for medical observation for 14 days.

4. How to identify asymptomatic infected persons? 

Asymptomatic infected persons are mainly identified proactively through the following ways:

(1) Proactive nucleic acid tests for people under medical observation who were traced to have had close contact with confirmed COVID-19 patients;

(2) Proactive nucleic acid tests for people who were traced to be related to COVID-19 case clusters according to relevant investigations;

(3) Proactive nucleic acid tests for people who were traced to have been exposed to sources of COVID-19 infection;

(4) Proactive nucleic acid tests for people who had a history of travel or residence in the COVID-19 outbreak areas home or abroad.

5. How to evaluate the risks posed by asymptomatic infected persons, and how to prevent and control the spread of COVID-19 caused by these persons?

Asymptomatic infected persons pose risks of the spread of COVID-19.

(1) The spread is latent. As asymptomatic infected persons do not exhibit any obvious symptoms of COVID-19, it is hard to identify them among crowds, and correspondingly, it is hard to prevent the spread of COVID-19 caused by them.

(2) The symptoms are subjective. Some asymptomatic infected persons only exhibit mild symptoms of COVID-19 or even exhibit non-typical symptoms. They may consider themselves not being infected with COVID-19, and will not seek medical treatment proactively, and therefore will be hard to be detected in the daily diagnosis.

(3) The identification has limitations. Nucleic acid tests and serology tests are not able to identify all asymptomatic infected persons because there exists a window period from getting infected with COVID-19 to generating detectable antibodies. Those having been identified so far were mainly detected when they underwent tests because they were traced to have had close contact with confirmed patients, be related to case clusters, be exposed to sources of infection, or had a history of travel or residence in high-risk regions. Some asymptomatic infected persons remain hard to identify.

It is therefore important to step up efforts to identify asymptomatic infected persons. Existing screening processes shall be intensified, and the scale of screening shall be expanded to include persons in close contact with confirmed cases and asymptomatic cases, key regions and key groups. Those being identified as asymptomatic infected persons shall be quarantined and undergo medical observation in strict accordance with the “early detection, early reporting, early isolation, and early treatment” principles. Those who have had close contact with asymptomatic infected persons shall also be quarantined for medical observation.

As some asymptomatic infected persons will never exhibit symptoms of COVID-19, it is impractical to make the identification and quarantine of asymptomatic infected persons the main measure. Our emphasis will continue to be laid on the identification and quarantine of confirmed patients while enhancing management on those who have had close contact with the confirmed patients.

China’s experience has manifested that, if patients are being identified and quarantined in time, and measures such as reducing contact with people are implemented, the spread of COVID-19 can basically be curbed.

6. What measures will be taken to strengthen the prevention and control of asymptomatic COVID-19 infections?

First, improve the prevention and treatment plans. A certain proportion of samples will be taken from areas severely affected by COVID-19 to investigate asymptomatic infected persons and conduct epidemiological analysis and research so as to improve prevention and control measures and enhance the prevention, control and treatment plans. Scientific measures will be taken to cope with risks of contagion caused by asymptomatic infected persons and contain further possible spread of the virus.

Second, intensify screening and detection. The screening will be stepped up in a targeted manner and the detection range will be expanded to people in close contact with confirmed patients and asymptomatic infected persons, key areas and key groups. The monitoring of key cities, key groups and key venues should be intensified while taking into consideration the resumption of work, production and schools, to identify hidden risks as much as possible. Efforts should be made to prevent cross-border transmission, and all travelers entering the country should take nucleic acid tests. Once an asymptomatic infected person is identified, an epidemiological investigation should be carried out to trace the source and related information should be released in an open and transparent way.

Third, strengthen management and treatment. Once an asymptomatic infected person is identified, the patient should be put under collective quarantine and medical management, as required by the principles of “early detection, early reporting, early isolation, and early treatment”. People who have had close contact with the infected person should be put under quarantine for medical observation as well. If any of them shows symptoms of COVID-19, he/she should be transferred to a designated hospital for treatment.

Fourth, intensify mass prevention and control. The public and the government should work together. More efforts should be made to promote knowledge on epidemic prevention among the public and guide the public in scientific prevention and protection. Training should be held extensively to improve the epidemic prevention and control capability of CDC personnel, medical staff and community staff at the grass-roots level. From April 1, information on asymptomatic infections including the report of new cases, their development into symptomatic cases, and the management of the cases will be released in the COVID-19 updates in response to public concerns.

7. What personal protective measures should be taken?

The public should strengthen the self-protection and health awareness, and improve environmental sanitation as well as personal hygiene habits, adopting a healthy lifestyle including washing hands regularly, wearing face masks, sanitizing hands, keeping at least one meter away from others, keep windows open for ventilation, regular disinfection, packing food in separate servings, avoiding crowded places while sick, and wearing face masks properly.

The public should engage in the patriotic health campaign. For protecting the health of ourselves and others, health knowledge shall be disseminated to every family and individual. The public shall develop good hygiene habits, adopt a civilized, healthy and green lifestyle, and improve mental as well as physical health.

Don’t panic if you test positive in nucleic acid tests and cooperate with medical institutions in health monitoring, quarantine and medical observation. If you show any symptoms like fever or cough, please make timely reports and accept standard treatment in a medical institution.

Foreign Affairs Office of Shenzhen Municipal People’s Government

Shenzhen Municipal Health Commission

April 2, 2020