September 27, 2020

COVID 2019 asymptomatic infections across the Worldcan it be a Time Bomb for Future Pandemic Recurrence? A Systematic Review of surveillance strategies


Background: COVID 2019 Infection can be considered a disease typically following the Iceberg Phenomenon, where actual large no

of submerged cases are inside and can become a threat to human beings as immunity development to SARS –CoV-2 cannot be forever. Studies across the world have suggested that out of many important research questions- the problem of asymptomatic and presymptomatic virus shedding is one of the grayest areas in the management of the COVID 20019 pandemic across the world.
Objective: Unrecognized threat of Incubatory carriers, as well as asymptomatic cases becoming a re-infection pool to the Global Community, can be very dangerous for the whole world. So a strategy for further Management of asymptomatic and presymptomatic CORONA +ve cases needs urgent appraisal if we have to prevent future recurrence of COVID 2019 Pandemic. That why systematic research is crucial in this regard, as attempted by authors in this article.
Material & methods: As per PRISMA(2009) guidelines protocol, a search of various kinds of studies in any form; using five key search words: ‘Asymptomatic’,
“Presymptomatic” “COVID 2019 Infection Surveillance, Pandemic, Recurrence ” was done in all health-related websites of Google, PubMed, EMBASE, MEDLINE, Global Health, Biomed-Central, Web of Science, Cochrane Library, world library – World-Cat, from 1 January 2020 to 25th April 2020 for systematic-review, followed by MetaAnalysis.
Results: Out of a wide variety of 31 studies available in literature related to this topic,20 were found to be eligible for issues synthesis, from which 2 crucial themes of Surveillance of Symptomatic and Asymptomatic & Presymptomatics emerged. Symptomatic surveillance was good in the form of Isolation and Quarantine across the World; but the real problem was of Asymptomatic post-discharge surveillance, which was only in the nascent stage in many countries across the world including developing countries such as India.

Conclusion: Lack of asymptomatic post-discharge surveillance may cause real havoc in the future, if no strategy is chalked out by governments across the World, leading to possible recurrence of the COVID 2019 Pandemic. However, the authors suggest more future research studies before we can say it very definitively that it will certainly happen.

Symptomatic transmission refers to transmission from a person while they are experiencing symptoms. Preliminary data suggests that people may be more contagious around the time of symptom onset as compared to later on in the disease. In a small number of case reports and studies, the pre-symptomatic transmission has been documented through contact tracing efforts and enhanced investigation of clusters of confirmed cases. 12-17 This is supported by data suggesting that some people can test positive for COVID-19 from 1-3 days before they develop symptoms.6,16 Thus, it is possible that people infected with COVID-19 could transmit the virus before significant symptoms develop. It is important to recognize that presymptomatic transmission still requires the virus to be spread
via infectious droplets or through touching contaminated surfaces. There are few reports of laboratory-confirmed cases who are truly asymptomatic, and to date, there has been no documented asymptomatic transmission. This does not exclude the possibility that it may occur. Asymptomatic cases have been reported as part of contact tracing efforts in some countries. COVID-19 infection so can range from asymptomatic and mild illness to severe illness. Most of the patients have an uncomplicated illness, mild to moderate pneumonia. China CDC has published data on COVID-19 which showed 80.9% cases were mild [21]. New evidence has emerged from China indicating that the large majority of coronavirus infections do not result in symptoms [22]. In summary, there are variations
across individuals in the clinical manifestations of COVID19 and we should pay attention to how to prevent people from being infected by asymptomatic patients and patients who were in their incubation period. A large number of patients infected with the virus who show few or no symptoms—estimated to be as high as 80% — complicates fighting the disease, forcing health care workers worldwide to shift their focus from containing the disease to mitigation [23].

There is clear evidence of asymptomatic infection with COVID-19. Estimates of the proportion of laboratory-confirmed cases who are asymptomatic may vary by age group, study the setting, and study methodology ranging from 1.2% (China), 6.4% (Italy), 12.9% (pediatric cases in China), 13.0% (longterm care facility in Washington State), and 17.9% (modeled estimate based on data from the Diamond Princess cruise ship). The extent to which screening is undertaken in group exposures and for contacts of cases, as well the duration of follow-up to ensure asymptomatic individuals do not subsequently develop symptoms will also influence the proportion of cases who are asymptomatic. There is some limited evidence of transmission from people who are asymptomatic and never develop symptoms, and more evidence of transmission from people who are in their incubation period (i.e. people who transmit infection while asymptomatic, but prior to their development of symptoms) [24]. Globally, too, there is enough evidence that suggests that people who never develop symptoms can transmit the virus. Studies from around the world published in the past weeks reveal the spread by “invisible sources” as a fresh challenge in the fight against Covid-19. This makes it much harder to trace and isolate everyone with the disease before they start transmitting it to others. Public health experts say these invisible sources of contagion must be fact [2]. Persons with co-morbidities should be shielded from close contact with mobile members of the family,” he said. Earlier the WHO had said that pre-symptomatic or asymptomatic transmission of the new coronavirus was “relatively rare”. However, new studies from Japan, Italy, South Korea, and Washington state — have suggested that silent spreaders can be just as dangerous to a community.[z2]Although for most people COVID-19 causes only mild illness, it can make some people very ill. More rarely, the disease can be fatal. Older
people and those with preexisting medical conditions (such as high blood pressure, heart problems, or diabetes) appear to be more vulnerable. Public health efforts are targeted at both interrupting further transmission and monitoring the spread of COVID-19. As reports of asymptomatic cases increase, the need for reliable serology testing is becoming more urgent. There are a number of groups working on this and developments are being monitored [25]. Researchers also suspect that there is an undetected pool of people who have mild or no symptoms. That is because an increasing number of infected people have not traveled to epidemic hotspots, or come into contact with people with confirmed cases of COVID-19.


This is different from unreported cases, those that are missed because authorities are not carrying out enough tests or people in the early stages of the virus who are not yet showing symptoms. A new study suggests there were 37,400 people with the virus in Wuhan who authorities did not know about, and who had mild or no symptoms but could still be contagious [5] In Iceland, which says it has tested a higher proportion of inhabitants than any other country,
about half those who tested positive for COVID-19 have no symptoms. Separately, the South China Morning Post reports that the number of “silent carriers” – people who are infected by the new coronavirus but show delayed or no symptoms –could be as high as one-third of those who test positive [5]. Now researchers are trying to determine whether people infected with COVID-19 but that show no symptoms can infect others. Preliminary findings seem to suggest they can. A study of Yuanyuan Xing et al. [26] from China reveals that after fulfilling the Chinese current criteria for discharge, it took few days for the immune system to completely eliminate the residual viruses in the body. During this period, the virus may rebound and test positive, but the patients were asymptomatic and
chest CT showed no deterioration. If the patients’ immunity decreases, there is a risk of a relapse. The new revelation of asymptomatic or mildly symptomatic infection in developing countries such as India has also generated Urgent concerns with the ICMR body. While ICMR officials do not recommend mass testing in India, given the size and scale of the country, experts familiar with the development said the door-to-door surveillance model is being examined.“It’s not easy to test everyone. But the model of door-to-door surveillance used for polio can be replicated here. The fact that India continues to be polio-free indicates the robustness of the in case of Covid-19, the possibility of monitoring people aged 50 years and more are being considered. “The silent spreaders are unknowingly infecting others. There is a need to strictly monitor the 50 plus population, which has the majority of positive cases,” added this person. Any such
exercise will take a long time and be expensive. Door-to-door surveillance will prove to be “costly and unachievable” in a country like India. According to WHO(2020) report that Countries that routinely conduct primary care or hospital-based sentinel surveillance for ILI, ARI, SARI, or pneumonia should continue to collect the respiratory specimens using existing case definitions through sentinel or syndromic networks. Laboratories should continue testing routine sentinel site samples, as well as non-sentinel samples for influenza, with the addition of testing for COVID-19. Until we know more about the temporal patterns of transmission, all countries are encouraged to conduct year-round surveillance for COVID-19. It is recommended to use the WHO’s case definition for ILI and SARI for COVID-19 surveillance.

It is probable that some COVID-19 infections may be missed due to the requirement of fever as a criterion. This is
acceptable since we are monitoring for general trends and not estimating the burden of illness, and it is likely that fever will
enrich the viral yield. The following strategies can be utilized strengthened for asymptomatic surveillance GISRS surveillance: Influenza and COVID-19 are both respiratory viruses with similar clinical presentations GISRS is a well-established network of more than 150 national public health laboratories in 125 countries which is monitoring the epidemiology and virologic evolution of influenza disease
and viruses. Till 25 March 2020, approximately 85% of more than 220 national public health laboratories currently testing
for COVID-19 globally are laboratories closely associated with GISRS. Utilizing the GISRS system can be an efficient and cost-effective approach to enhancing COVID-19 surveillance.
a) Developed countries( e.g. US)
a) Outpatient Influenza-Like Illness Network (ILINet) and
National Syndromic Surveillance Program (NSSP)
b)National Polio Surveillance Programmes
b) Developing Countries ( e.g. India) a) NPSP based surveillance system
b) AADHAR BASED IDSP Surveillance
c) Door to Door Surveillance by Primary Health care Workers
d) Sentinel Surveillance at CHC/Block level


National surveillance systems should initially aim at rapidly detecting cases and assessing community transmission. As the epidemic progresses, surveillance should monitor the intensity, geographical spread, and the impact of the epidemic on the population and healthcare systems and assess the effectiveness of measures in place. In circumstances with capacity shortages and strict implementation of social distancing measures, surveillance should focus on severe acute respiratory infections, sentinel surveillance in outpatient clinics, or collection of data through telephone helplines. A strategic approach based on an early and rigorous application of these measures will help reduce the burden and pressure on the healthcare system, and in particular on hospitals, and will allow more time for the testing of therapeutics and vaccine development [27]. According to WHO( 2020) Report [x]- the ultimate objectives
of any global surveillance should be to 1. Monitor trends in COVID-19 disease at national and global levels. 2. Rapidly detect new cases in countries where the virus is not circulating, and monitor cases in countries where the virus has started to circulate. 3. Provide epidemiological information to conduct risk assessments at the national, regional, and global levels. 4. Provide epidemiological information to guide preparedness and response measures. Such surveillance strategies need replication with regard to asymptomatics also if we have to prevent future recurrence of COVID 2019 Global Pandemic. In China, it is now followed that the Designated hospitals
should make plans for patients’ return visits and re-testing for the next two to four weeks following their discharge, The sputum samples are more reliable and should be the first choice for re-testing. A high-powered committee headed by Chinese Premier Li Keqiang which was leading the efforts to contain the virus since January has also called for intensified detection and prompt response to asymptomatic cases meaning people infected with coronavirus but showed no symptoms. Screening of asymptomatic infections should be stepped up, targeting close contacts of confirmed patients, people involved in cluster outbreaks, those exposed to Covid-19, and travelers from areas with high risks of infections, it said. The regulation required nationwide hospitals and disease control departments to take prompt actions once asymptomatic carriers are detected. Once verified, asymptomatic carriers will be put under
concentrated medical observation for 14 days and can only. India’s Discharge Policy of nCoV Cases also needs reconsideration. If the laboratory results for nCOV are negative, the discharge of such patients will be governed by his provisional/confirmed diagnosis and it is up to the treating physician to make a decision. The case shall still be monitored for 14 days after their last contact with a confirmed 2019-nCoV case. The case shall be discharged only after evidence of chest radiographic clearance and viral clearance in respiratory
samples after two specimens test negative for nCOV within a period of 24 hours. India’s top medical research body is grappling with the
problem posed by “silent spreaders” and examining the feasibility of starting ‘door-to-door’ surveillance to monitor and test older people at high risk who don’t have symptoms [22]. While ICMR officials do not recommend mass testing in India, given the size and scale of the country, experts familiar with the development said the door-to-door surveillance model is being examined.
Salivary Surveillance can also be a new Option Because saliva can be provided by patients without any invasive procedures,
the use of saliva specimens will reduce the risk of nosocomial transmission of 2019-n CoV and is ideal for situations in which
nasopharyngeal specimen collection may be contraindicated. As per a study in literature, Saliva can be a promising noninvasive
specimen for diagnosis, monitoring, and infection control in patients with 2019-nCoV infection [28]. Our systematic review reveals that as per recommendations from many studies-Asymptomatic carriers during the incubation period can be a potential infection source of
COVID-19. As Person-to-person transmission has been documented; asymptomatic carriers should be a focus for disease prevention So it gets almost clear from studies in literature- COVID-19 can be transmitted by asymptomatic carriers during the incubation period [29-35]. Our systematic review therefore finally reveals that both developed & developing countries such as India lacks a Proper Post Discharge Surveillance system of Asymptomatic Corona + ve cases, which can be detrimental in the form of future recurrence of Epidemic in countries like India where the Population density is high and virus explosive Hot spot areas such as Dharavi Slum of Mumbai & Slums of Delhi can be a dangerous recurrent area in future [35-44].

Conclusion: Lack of asymptomatic post-discharge surveillance can be devastating for the future, if no Proper-surveillance strategy
is chalked out by governments across the World, leading to possible recurrence of the COVID 2019 Pandemic. However, the authors
suggest more research studies in the future on an urgent basis, before we can say it very definitively.

1. No symptoms in 80% of COVID cases raise concerns. Link:

2. Chan JFW, Yuan S, Kok KH, To KKW, Chu H, et al. (2020) A familial cluster of pneumonia associated with the 2019 novel coronavirus indicating person-toperson transmission: a study of a family cluster. Lancet 395: 514-523. Link:

3. Yuen KS, Ye ZW, Fung SY, Chan CP, Jin DY (2020) SARS-CoV-2 and COVID-19: The most important research questions. Cell Biosci 10: 40. Link:

4. Lauer SA, Grantz KH, Bi Q, Jones FK, Jones FK, Zheng Q, et al. (2020) The Incubation Period of Coronavirus Disease 2019 (COVID-19) From Publicly Reported Confirmed Cases: Estimation and Application. Ann Intern Med. Link:

5. Bai Y, Yao L, Wei T, Tian F, Jin DY, et al. (2020) Presumed asymptomatic carrier transmission of COVID-19. JAMA 323: 1406-1407. Link

6. Zhou P, Yang XL, Wang XG, Hu B, Zhang L, et al. (2020) A pneumonia outbreak associated with a new coronavirus of probable bat origin. Nature 579: 270-273. Link:

7. Lam TTY, Shum MHH, Zhu HC, Tong YG, Ni XB, et al. (2020) Identification of 2019-nCoV related coronaviruses in Malayan pangolins in southern China. BioRxiv. Link:

8. Lu R, Zhao X, Li J, Niu P, Yang B, et al. (2020) Genomic characterization and epidemiology of 2019 novel coronavirus: implications for virus origins and receptor binding. Lancet. Link:

9. The Novel Coronavirus Pneumonia Emergency Response Epidemiology TeamVital surveillances (2020) The epidemiological characteristics of an outbreak of 2019 novel coronavirus diseases (COVID-19)—China. China CDC Weekly. 2: 113-122.

10. Wang D, Hu B, Hu C, Zhu F, Liu X, et al. (2020) Clinical characteristics of 138 hospitalized patients with 2019, novel coronavirus–infected pneumonia in Wuhan China. JAMA 323: 1061-1069. Link:

11. Novel coronavirus disease 2019 (COVID-19) pandemic: increased transmission in the EU/EEA and the UK – sixth update. Link:

12. CDC COVID Data Tracker. CDC. Link:

13. Heimdal I, Moe N, Krokstad S, Christensen A, Skanke LH, et al. (2019) Human coronavirus in hospitalized children with respiratory tract infections: a 9-year population-based study from Norway. J Infect Dis 219: 1198–1206. Link:

14. Chan JFW, Yuan S, Kok KH, To KKW, Chu H, et al. (2020) A familial cluster of
pneumonia associated with the 2019 novel coronavirus indicating person-toperson transmission: a study of a family cluster. Lancet 395: 514-523. Link:

15. WHO (2020) Global surveillance for COVID-19 caused by human infection with COVID-19 virus. Link:

16. Heneghan C, Brassey J, Jefferson T (2020) COVID-19: What proportion are asymptomatic?. Link:

17. Heneghan C, Brassey J, Jefferson T (2020) COVID-19: What proportion are asymptomatic?. Link:

18. Hu Z, Song C, Xu C, Jin G, Chen Y, et al. (2020) Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing, China. Sci China Life Sci 63: 706-711. Link:

19. Day M (2020)Covid-19: four-fifths of cases are asymptomatic, China figures indicate. BMJ 369: m1375. Link:

20. Coronavirus disease 2019 (COVID-19) Situation Report – 73. Link:

21. Wu Z, McGoogan JM (2020) Characteristics of and Important Lessons From the Coronavirus Disease 2019 (COVID-19) Outbreak in China: Summary of a Report of 72 314 Cases From the Chinese Center for Disease Control and Prevention. JAMA 323: 1239–1242. Link:

22. Nishiura H, Kobayashi T, Suzuki A, Jung SM, Hayashi K, et al. (2020) Estimation of the asymptomatic ratio of novel coronavirus infections (COVID-19). International Journal of Infectious Diseases 94: 154-155. Link:

23. Lai CC, Liu HY, Wang CY, Hsueh SC, Yen MY, et al. (2020) Asymptomatic carrier state, acute respiratory disease, and pneumonia due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2): Facts and myths. Journal of Microbiology, Immunology, and Infection 53: 404-412. Link:


More Information:












Leave a Reply

Your email address will not be published. Required fields are marked *