Home Print this page Email this page
Users Online: 21509
Home About us Editorial board Search Ahead of print Current issue Archives Submit article Instructions Subscribe Contacts Login 


 
 Table of Contents  
REVIEW ARTICLE
Year : 2021  |  Volume : 10  |  Issue : 1  |  Page : 11-16

COVID-19: The enigma of asymptomatic carriers and silent transmission


Department of Public Health and Community Medicine, Faculty of Medicine, Mansoura University, Mansoura, Egypt

Date of Submission11-Jul-2020
Date of Decision07-Aug-2020
Date of Acceptance10-Sep-2020
Date of Web Publication2-Feb-2021

Correspondence Address:
Abdel-Hady El-Gilany
Faculty of Medicine, Mansoura University, Mansoura 35516
Egypt
Login to access the Email id

Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijhas.IJHAS_135_20

Rights and Permissions
  Abstract 


The presence of asymptomatic carriers is well known in the COVID-19. These carriers play a significant role in the disease transmission. Little is known about its magnitude, types, detection, and management. This narrative review highlights all these aspects of asymptomatic COVID-19 carriers. Much is still unknown about asymptomatic carriers in COVID-19 and its contribution in the silent spread of infection. A literature of three electronic databases with prespecified search terms was done to include the status quo data on asymptomatic carriers in COVID-19 infection. This narrative review will be useful for epidemiologists, clinicians, policymakers as well as the public in general.

Keywords: Asymptomatic carrier, COVID-19, presymptomatic carrier-silent spread


How to cite this article:
El-Gilany AH. COVID-19: The enigma of asymptomatic carriers and silent transmission. Int J Health Allied Sci 2021;10:11-6

How to cite this URL:
El-Gilany AH. COVID-19: The enigma of asymptomatic carriers and silent transmission. Int J Health Allied Sci [serial online] 2021 [cited 2024 Mar 29];10:11-6. Available from: https://www.ijhas.in/text.asp?2021/10/1/11/308581




  Introduction Top


COVID-19 is a novel human coronavirus identified in China in December 2019. Much is unknown about its basic epidemiology, including the asymptomatic carriers, which is important for prevention and control activities. The key to prevent silent spread of the virus is to understand the symptomless carriers. Many scholars believe that a large number of asymptomatic carriers are responsible for rapid spread of COVID-19.[1],[2],[3],[4] Asymptomatic carriers or silent spreaders refer to people who tested positive for the coronavirus but develop no symptoms. They are infectious and pose a risk of spreading infection to others. The prevalence of asymptomatic carriers is a challenge aspect of the coronavirus pandemic. Many studies reported asymptomatic people seems to have the same viral load as cases with symptoms. Ultimately, testing blood for antibodies in community surveys is the only way to really find out the prevalence of asymptomatic COVID-19 carriers. These tests are not available nowadays and being developed in several countries.[3],[5],[6],[7] The lack of a reliable diagnostic test for the timely detection of asymptomatic carriers is a major limitation to control the spread of the disease.


  Search Strategy Top


This is a status quo review that included the current research related to COVID-19 carriers. A literature search was conducted with the following three electronic databases: PubMed, Scopus, and Google Scholar. Search terms included “COVID-19,” “Types of carriers,” “prevalence of asymptomatic carriers” “sites of viral carriage,” “Asymptomatic carrier,” “detection of carriers,” “importance of carriers,” and “control of asymptomatic carriers,” and these terms were used in different combinations. All articles and books published in English were read and assessed for inclusion.


  Study Rationale Top


Despite of their epidemiological significance, the effects of carriers on the transmission dynamics of COVID-19 received inadequate attention in the mathematical research modeling. Comprehension of the natural history of carriers and their contribution to spread of infection is a prerequisite for formulating effective measures for prevention and control. The ratio of in-apparent to apparent infection in COVID-19 is definitely unknown. There is no public data about the number of asymptomatic carriers in most of the countries. Understanding the natural history of asymptomatic or presymptomatic infection will help in personalized risk stratification and reveal the protective immunity, whether artificial or natural.


  Classification and Types of Carriers Top


For some infectious diseases, there are subjects who can transmit the infection but do not show any symptoms and they are called carriers or asymptomatic carriers and the term “symptomatic infection” concerns those with observable clinical manifestation.[8] Infectious disease carriers should be differentiated from a related term; genetic carriers who carry the disease on their recessive genes and only pass it to their children and are not contagious.[9]

Epidemiologically, a carrier is an animal or person that harbors and spreads an infectious agent without apparent clinical manifestations. This carrier may by immune person with an infection that is in-apparent throughout its course (also known as passive carrier, healthy carrier, or subclinical case), or during the incubation or convalescence period of an individual with a clinically recognizable disease (called incubatory or convalescent carrier; respectively). In both circumstances the carriage state may last for short or long duration (transient/temporary or chronic carrier; respectively) or intermittent carrier who discharges organism at intermittent intervals.[10]

Epidemiologists have described three types of silent spreaders of COVID-19, i.e., asymptomatic, presymptomatic, and convalescent carriers:[2],[3],[11],[12],[13],[14],[15],[16],[17],[18],[19]

Asymptomatic carriers

Asymptomatic carriers are people without any symptom at all while incubating the virus in their bodies. They have no symptoms or clinical signs throughout the 14-day quarantine. They transmit the virus to a lot of people and fuel the pandemic. They may become immune despite they never have any symptoms during their infections. However, currently, it is difficult to identify truly asymptomatic carriers and their immune status.

Presymptomatic carriers (incubatory carriers)

These people do not develop any symptoms for almost a week after contracting the novel coronavirus. They later display symptoms such as coughing, fever, and exhaustion. The levels of the virus are high in respiratory discharges and spread infection during the presymptomatic period that can last from days to weeks prior to the characteristic symptoms of COVID-19.

Postsymptomatic (convalescent/postconvalescence) carriers

Individuals with a clinically recognizable disease who spread infection for different periods after disappearance of symptoms. The agent is not completely eliminated due to inadequate treatment or deficient immune response resulting in the carrier state.

A related term is the paradoxical carrier is a person who acquires the organism from another carrier. Asymptomatic and presymptomatic carriers should be differentiated from unreported and missed cases due to inadequate case finding.


  Sites of Carriage and Exit Top


This differs from a causative agent to another. The COVID-19 virus was detected in all parts of the respiratory tract and find exit with respiratory discharges. Furthermore, the virus was detected in intestine and some patients develop gastrointestinal symptoms. The initial investigations detected the virus in stool of some cases; though this is not a main route of spread during the outbreak. There is a low risk of catching COVID-19 from the feces of an infected person.[11],[12] Hands and surfaces can be contaminated with the virus and constitute a potential route of oral transmission.[20]


  Magnitude of Asymptomatic Carriers Top


Recent epidemiologic models found that asymptomatic or mild cases that pass undetected and not documented ranged from 5% to 85% of total infections in different studies. This variation is related to age group, study methods, study setting, extent of screening in the exposed and contacts, as well as duration of follow-up.[5],[13],[17],[21],[22],[23],[24],[25],[26],[27],[28],[29],[30],[31],[32],[33],[34],[35],[36],[37],[38]

However, most of these studies typically estimated the prevalence of asymptomatic carriers only at single points in time; other follow-up studies have shown that a large proportion of asymptomatic people with initially positive test develop symptoms later on.[39]

It was estimated that up to 86% of all infections were not documented and their transmission rate per person was 55% the transmission rate of documented infections. The undocumented infections were the source of 79% of the documented cases because of their greater numbers.[40] The actual prevalence of asymptomatic and mild infections will remain unknown until a cheap serological test, detecting the viral antibodies signaling previous infection, is available for routine use.[41]


  Detection of Carriers Top


It is usually possible to identify asymptomatic carriers. The Centers for Disease Control estimates that coronavirus can be picked up by a conventional test around 1–2 days before symptoms appear. This means people may have enough of the virus in their bodies to be detected by laboratory tests, but they might not feel sick yet.[42] COVID-19 carriers can be detected by polymerase chain reaction (PCR) for swabs from respiratory tract (nose, naso-pharynx, and oropharynx) or bronchial aspirate, as well as stool culture. Currently, no serologic detection is available.[11] However, caution should be taken as detected RNA may be a remnant of nonbiologically active virus not capable of transmitting infection.[39] As other corona viruses, it is possible most people are developing antibodies after recovery from COVID-19 that will offer some protection from reinfection,[43] however, no antibodies test was available yet.


  Importance of Carriers Top


The carrier is unapparent and spreads infection for different periods.[10] Chen et al.[44] raised the alarm of the existence of the transmissibility of the asymptomatic COVID-19 cases. However, He et al.[45] concluded that the relative transmissibility of asymptomatic persons could be smaller than that of the symptomatic patients. Furthermore, there is a high level of viral shedding in the upper respiratory tract among presymptomatic patients.[46],[47],[48] Presymptomatic transmission occurred 1–3 days before symptoms development.[49] It has been inferred that presymptomatic spread contributed up to 62% of transmissions even in the presence of control measures.[50]

Epidemiologically, carriers are more important than cases as their number may outnumber cases, they are difficult to recognize as they have no symptoms and unaware of being infected, they move freely (cases are restricted) and chronic carriers, if present, re-introduce infection, and contribute to endemicity. It is possible that asymptomatic carriers in COVID-19 may be responsible for what is known as community spread or transmission. Researchers failed to relate a large number of confirmed cases through the usual chains of transmission. Furthermore, there is an increasing number of positives in routine testing of respiratory samples for other indications.[51] Asymptomatic carriers generate speech droplets that are considered to be the mode of infection transmission.[52] However, the seriousness of a carrier as a source of infection depends on his occupation, dwelling conditions, and personal habits.[36]

The vague nature of asymptomatic carrier is closely related to the prevention and control of COVID-19.

Identifying asymptomatic carriers is useful to highlight those with higher risk of poorer outcomes from a given treatment or procedure, allowing possible deferral for care or amend treatment plans (e.g., hold immune suppressing treatment until infection resolved), and conserve the personal protective equipment to those who in need.

Light cases and asymptomatic carrier are not counted as COVID-19 cases and they will exacerbate the spread of infections. Those who develop symptoms should be reclassified as a confirmed case.

The incidence data only include symptomatic cases and the true magnitude of asymptomatic carrier remains unknown.

Asymptomatic carriers should be included in calculation of the basic reproduction number (R0). Kalajdzievska and Li[9] formulated a model for prediction R0 including the susceptible, carrier, symptomatically infectious and removed classes and the model yields a much higher R0.

With lack of direct evidence of asymptomatic carriers it is hard to interpret the epidemiological record with uncertainties about the carrier state.[53],[54] For example, estimating the duration of asymptomatic carrier is difficult due to limited data on exact time of catching infection and of subsequent viral clearance.[55]

The existence of asymptomatic carriers compromise the control efforts that depends on detecting infectious cases, for example, large-scale monitoring, isolating, and treating infectious cases.[56]

Asymptomatic carriers affect the usefulness of interventions targeting susceptible subjects because of difficultly in distinguishing between the two groups.[57]

Accidental treatment of these carriers could result in the emergence and spread of drug-resistant agents.[58],[59]


  Prevention and Control of Asymptomatic Carriers Top


The extent of asymptomatic or presymptomatic spread is definitely unknown. Asymptomatic surveillance (testing people without symptoms) is an important strategy to collect data on how COVID-19 is spread in the community. It should be stressed that the result is instant that is a negative person may develop symptoms or turn positive at a later time and needs re-testing.

The following are measures to be taken for prevention and control of asymptomatic carriers:[15],[28],[50],[60]

  1. Screening and detection of asymptomatic carriers should be stepped up by testing: (1) close contacts of confirmed cases; (2) people involved in investigations of clusters; (3) exposed people during tracing of the infection source; (4) people with history of travel or residence in areas endemic with COVID-19; and (5) during opportunistic screening and epidemiological investigation


  2. There is an argue for extending COVID-10 testing to include asymptomatic persons in high-risk and dangerous settings and enforce the general public to use face masks when in crowded outdoor or indoor spaces.[61] Hu et al.[62] highlighted the importance of contact tracing and longitudinal surveillance by PCR. Further isolation and continuous PCR testing are recommended to the patients after discharge. As serological assays are still not available, pooled PCR testing of a random community sample could allow for rapid assessment of the prevalence of clinical, missed and subclinical cases in the community[63],[64]

  3. Standardize reporting of asymptomatic carriers by all types and levels of health-care facilities
  4. Proper management of asymptomatic persons and they should be quarantined for 14 days or negative two successive swabs. Those who develop clinical manifestations of COVID-19 during this period should be reclassified as confirmed cases and given the standard treatment. A single center study found that asymptomatic COVID-19 infections have longer treatment cycle than moderate types of confirmed cases[65]
  5. Contacts of asymptomatic persons should be put under medical observation for 14 days.
  6. Health education and counseling the asymptomatic carriers and their contacts to follow the routine preventive measures
  7. All data should be available for research on epidemiology, infectivity, and transmission of asymptomatic carriers.



  Conclusions Top


There is an epidemiologic uncertainty of the possible spread of the virus by asymptomatically or presymptomatic-infected persons together with the lack of effective drugs to eliminate this carrier state. It is a challenge to consider the possible presence of a large number of infectious COVID-19 carriers without symptoms. Because they are symptomless, they are not a part of any prevention and treatment measures. Further specific models for COVID-19 infection and more data are needed to be employed to predict future disease load. Large scale contact tracing as well as community surveys are essential to assess the magnitude of the asymptomatic carriers. Further research is needed to find out the percentage of carriers, their types, duration of carriers states, mode of exit, their epidemiologic significance, and testing drugs for clearance of the carriage state. There is a need to develop and apply a standard protocol for the management of asymptomatic carriers of COVID-19.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Omrani AS. Coronavirus disease 2019: The story so far. Libyan J Med Sci 2020;4:52-7.  Back to cited text no. 1
  [Full text]  
2.
Guo YR, Cao QD, Hong ZS, Tan YY, Chen SD, Jin HJ, et al. The origin, transmission and clinical therapies on coronavirus disease 2019 (COVID-19) outbreak – An update on the status. Mil Med Res 2020;7:11.  Back to cited text no. 2
    
3.
ECDC. Coronavirus Disease 2019 (COVID-19) Pandemic: Increased Transmission in the EU/EEA and the UK – Seventh Update, 25 March 2020. Stockholm: ECDC, European Centre for Disease Prevention and Control; 2020.  Back to cited text no. 3
    
4.
Deep A, Yadav A, Sharma M, Mittal K, Mittal A.COVID-19: Epidemiology and virology. J Pediatr Crit Care 2020;7:S3-9.  Back to cited text no. 4
    
5.
Thomas-Rüddel D, Winning J, Dickmann P, OuartD, Kortgen A, Janssens U, et al. Coronavirus disease 2019 (COVID-19): Update for anesthesiologists and intensivists. Anaesthesist 2020;69:225-35. doi: 10.1007/s00101-020-00758-x.  Back to cited text no. 5
    
6.
Saxena SK, Kumar S, Maurya VK, Sharma R, Dandu HR, Bhatt M. Current insight into the novel coronavirus disease 2019 (COVID-19). In: Saxena SK, editor. Coronavirus Disease 2019 (COVID-19). Epidemiology, Pathogenesis, Diagnosis, and Therapeutics. Singapore: Springer: Springer Nature Singapore Private Limited; 2020.  Back to cited text no. 6
    
7.
Srivastava N, Baxi P, Ratho R, Saxena SK. Global trends in epidemiology of coronavirus disease 2019 (COVID-19). In: Saxena SK, editor. Coronavirus Disease 2019 (COVID-19). Epidemiology, Pathogenesis, Diagnosis, and Therapeutics. Singapore: Springer: Springer Nature Singapore Private Limited; 2020.  Back to cited text no. 7
    
8.
Chisholm RH, Campbell PT, Wu Y, Tong SY, McVernon J, Geard N. Implications of asymptomatic carriers for infectious disease transmission and control. R Soc Open Sci 2018;5:172341. doi: 10.1098/rsos.172341.  Back to cited text no. 8
    
9.
Kalajdzievska D, Li MY. Modeling the effects of carriers on transmission dynamics of infectious diseases. Math Biosci Eng 2011;8:711-22.  Back to cited text no. 9
    
10.
Merrill RM, Timmreck TS. Introduction to Epidemiology. 4th ed. Canada: Jones and Bartlett Publishers; 2006.  Back to cited text no. 10
    
11.
Rao S. Microbiology Notes; June, 2006. Available from: http://www.microrao.com/micronotes/carriers.htm. [Last accessed on 2020 May 24].  Back to cited text no. 11
    
12.
Aryal S. Source and Reservoir of Infection; 11 September, 2019. Available from: https://microbenotes.com/source-and-reservoir-of-infection/#Human_reservoir. [Last accessed on 2020 May 24].  Back to cited text no. 12
    
13.
Deshpande C. Asymptomatic Patients spreads COVID-19, Home Isolate Them; 22 May, 2020. Available from: https://timesofindia.indiatimes.com/city/nagpur/asymptomatic-patients-spread-covid-19-home-isolate-them/articleshow/75876928.cms. [Last accessed on 2020 Jun 06].  Back to cited text no. 13
    
14.
Health Information and Quality Authority. Evidence Summary for Asymptomatic Transmission of COVID-19; 21 April, 2020. Available from: https://www.hiqa.ie/sites/default/files/2020-04/Evidence-summary-for-asymptomatic-transmi ssion-of-COVID-19.pdf. [Last accessed on 2020 May 24].  Back to cited text no. 14
    
15.
Joint Taskforce on COVID-19 Prevention and Control, China State Council. Protocol for the Management of Asymptomatic Persons Infected with COVID-19 Virus. CCDC Weekly; 2020. Available from: http://www.chinacdc.cn/en/COVID19/202004/P020200412500050083414.pdf. [Last accessed on 2020 May 24].  Back to cited text no. 15
    
16.
Luo SH, Liu W, Liu ZJ, Zheng XY, Hong CX, Liu ZR, et al. A confirmed asymptomatic carrier of 2019 novel coronavirus. Chin Med J (Engl) 2020;133:1123-5.  Back to cited text no. 16
    
17.
Public Health Ontario (2020). COVID-19 – What We Know So Far About. Asymptomatic Infection and Asymptomatic Transmission. SYNOPSIS Version 4; 2020. Available from: https://www.publichealthontario.ca/-/media/documents/ncov/what-we-know-jan-30-2020.pdf?la=en. [Last accessed on 2020 May 24].  Back to cited text no. 17
    
18.
Ye F, Xu S, Rong Z, Xu R, Liu X, Deng P, et al. Delivery of infection from asymptomatic carriers of COVID-19 in a familial cluster. Int J Infect Dis 2020;94:133-8.  Back to cited text no. 18
    
19.
Sahu KK, Kumar R. Preventive and treatment strategies of COVID-19: From community to clinical trials. J Family Med Prim Care 2020;9:2149-57.  Back to cited text no. 19
  [Full text]  
20.
Yadav T, Saxena SK. Transmission Cycle of SARS-CoV and SARS-CoV-2. In: Saxena SK, editor. Coronavirus Disease 2019 (COVID-19).Epidemiology, Pathogenesis, Diagnosis, and Therapeutics. Singapore: Springer Nature Singapore Private Limited; 2020.  Back to cited text no. 20
    
21.
Al-Tawfiq JA. Asymptomatic coronavirus infection: MERS-CoV and SARS-CoV-2 (COVID-19). Travel Med Infect Dis 2020;35:101608. doi: 10.1016/j.tmaid.2020.101608.  Back to cited text no. 21
    
22.
Manyombe ML, Mbang J, Lubuma J, Tsanou B. Global dynamics of a vaccination model for infectious diseases with asymptomatic carriers. Math Biosci Eng 2016;13:813-40.  Back to cited text no. 22
    
23.
WHO. Coronavirus Disease 2019 (COVID-19) Situation Report -98. Available from: https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200427-sitrep-98-covid-19.pdf?sfvrsn=90323472_4m. [Last accessed on 2020 Apr 28].  Back to cited text no. 23
    
24.
Lavezzo E, Franchin E, Ciavarella C, Cuomo-Dannenburg G, Barzon L, Del Vecchio C, et al. Suppression of COVID-19 Outbreak in the Municipality of Vo', Italy. Nature 2020;584:425-9.  Back to cited text no. 24
    
25.
Day M. Covid-19: Four fifths of cases are asymptomatic, China figures indicate. BMJ 2020;369:m1375.  Back to cited text no. 25
    
26.
Heneghan C, Brassey J, Jefferson T. COVID-19: What Proportion are Asymptomatic? Centre for Evidence-Based Medicine. University of Oxford: University of Oxford; 6 April, 2020. Available from: https://www.cebm.net/covid-19/covid-19-what-proportion-are-asymptomatic/. [Last accessed on 2020 May 28].  Back to cited text no. 26
    
27.
Qiu H, Wu J, Hong L, Luo Y, Song Q, Chen D. Clinical and epidemiological features of 36 children with coronavirus disease 2019 (COVID-19) in Zhejiang, China: An observational cohort study. Lancet Inf Dis 2020;20:689-96.  Back to cited text no. 27
    
28.
Mizumoto K, Kagaya K, Zarebski A, Chowell G. Estimating the asymptomatic proportion of coronavirus disease 2019 (COVID-19) cases on board the Diamond Princess cruise ship, Yokohama, Japan, 2020. Euro Surveill 2020;25(10):2000180.  Back to cited text no. 28
    
29.
Nishiura H, Kobayashi T, Miyama T, Suzuki A, Jung SM, Hayashi K, et al. Estimation of the asymptomatic ratio of novel coronavirus infections (COVID-19). Int J Infect Dis 2020;94:154-5.  Back to cited text no. 29
    
30.
Mahapure KS, Kulkarni NS. Asymptomatic transmission of severe acute respiratory syndrome-coronavirus 2 within a family cluster of 26 cases: Why quarantine is important? J Glob Infect Dis 2020;12:115-6.  Back to cited text no. 30
    
31.
Alberta Health Services 2020. COVID-19 Scientific Advisory Group Rapid Response Report. Key Research Question: What is the Evidence Supporting the Possibility of Asymptomatic Transmission of SARS-CoV-2? Available from: https://www.albertahealthservices.ca/assets/info/ppih/if-ppih-covid-19-rapid-response-asymptomatic-transmission.pdf. [Last updated on 2020 Apr 13; Last accessed on 2020 May 28].  Back to cited text no. 31
    
32.
Yu X, Yang R. COVID-19 transmission through asymptomatic carriers is a challenge to containment. Influenza Other Respir Viruses 2020;14:474-5.  Back to cited text no. 32
    
33.
Kim GU, Kim MJ, Ra SH, Lee J, Bae S, Jung J, et al. Clinical characteristics of asymptomatic and symptomatic patients with mild COVID-19. Clin Microbiol Infect 2020;26:948.e1-00.  Back to cited text no. 33
    
34.
Arons MM, Hatfield KM, Reddy SC, Kimball A, James A, Jacobs JR, et al. Presymptomatic SARS-CoV-2 infections and transmission in a skilled nursing facility. N Engl J Med 2020;382:2081-90.  Back to cited text no. 34
    
35.
Barajas RF Jr., Rufener G, Starkey J, Duncan T, Fuss C. Asymptomatic COVID-19: What the neuroradiologist needs to know about pulmonary manifestations. AJNR Am J Neuroradiol 2020;41:966-8.  Back to cited text no. 35
    
36.
Bai Y, Yao L, Wei T, Tian F, Jin DY, Chen L, et al. Presumed asymptomatic carrier transmission of COVID-19. JAMA 2020;323:1406-7.  Back to cited text no. 36
    
37.
Chan JF, Yuan S, Kok KH, To KK, Chu H, Yang J, et al. A familial cluster of pneumonia associated with the 2019 novel coronavirus indicating person-to-person transmission: A study of a family cluster. Lancet 2020;395:514-23.  Back to cited text no. 37
    
38.
Huang L, Zhang X, Zhang X, Wei Z, Zhang L, Xu J, et al. Rapid asymptomatic transmission of COVID-19 during the incubation period demonstrating strong infectivity in a cluster of youngsters aged 16-23 years outside Wuhan and characteristics of young patients with COVID-19: A prospective contact-tracing study. J Infect 2020;80:e1-13.  Back to cited text no. 38
    
39.
CDC. Centers for Disease Control and Prevention report, Asymptomatic and Presymptomatic SARS-CoV-2 Infections in Residents of a Long-Term Care Skilled Nursing Facility-King County, Washington; March, 2020. Available from: https://www.cdc.gov/mmwr/volumes/69/wr/mm6913e1.htm. [Last accessed on 2020 May 28].  Back to cited text no. 39
    
40.
Li R, Pei S, Chen B, Song Y, Zhang T, Yang W, et al. Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV-2). Science 2020;368:489-93.  Back to cited text no. 40
    
41.
Public Health Factsheet (2020) COVID-19novel coronavirus. Understanding the Spread of COVID-19: Asymptomatic Surveillance. Available from: https://sharedhealthmb.ca/files/covid-19-asymptomatic-info-sheet-patients.pdf. [Last accessed on 2020 May 28].  Back to cited text no. 41
    
42.
CDC. Coronavirus Disease 2019 (COVID-19) Clinical Questions about COVID-19: Questions and Answers. Updated; 12 May, 2020. Available from: https://www.cdc.gov/coronavirus/2019-ncov/hcp/faq.html. [Last accessed on 2020 May 25].  Back to cited text no. 42
    
43.
Johns Hopkins University. Asymptomatic Spread Makes Testing key for COVID-19 fight; 2020 May 15. Available from: https://www.futurity.org/asymptomatic-covid-19-immunity-viruses-2365852-2/. [Last accessed on 2020 May 28].  Back to cited text no. 43
    
44.
Chen Y, Wang AH, Yi B, Ding KQ, Wang HB, Wang JM, et al. Epidemiological characteristics of infection in COVID-19 close contacts in Ningbo city. Zhonghua Liu Xing Bing Xue Za Zhi 2020;41:667-71.  Back to cited text no. 44
    
45.
He D, Zhao S, Lin Q, Zhuang Z, Cao P, Wang MH, et al. The relative transmissibility of asymptomatic COVID-19 infections among close contacts. Int J Infect Dis 2020;94:145-7.  Back to cited text no. 45
    
46.
Wölfel R, Corman VM, Guggemos W, Seilmaier M, Zange S, Müller MA, et al. Virological assessment of hospitalized patients with COVID-2019. Nature 2020;581:465-9.  Back to cited text no. 46
    
47.
He X, Lau E, Wu P, Deng X, Wang J, Hao X, et al. Temporal dynamics in viral shedding and transmissibility of COVID-19. Nature Med 2020;26:672-5.  Back to cited text no. 47
    
48.
Aguilar JB, Faust JS, Westafer LM, Gutierrez JB. Investigating the Impact of Asymptomatic carriers on COVID-19 Transmission. Coronavirus COVID-19 Publications; 2020. Available from: https://escholarship.umassmed.edu/covid19/6. [Last accessed on 2020 May 26].  Back to cited text no. 48
    
49.
Wei WE, Li Z, Chiew CJ, Yong SE, Toh MP, Lee VJ. Presymptomatic Transmission of SARS-CoV-2-Singapore, January 23-March 16, 2020. MMWR Morb Mortal Wkly Rep 2020;69:411-5.  Back to cited text no. 49
    
50.
Ganyani T, Kremer C, Chen D, Torneri A, Faes C, Wallinga J, et al. Estimating the generation interval for COVID-19 based on symptom onset data. medRxiv 2020. medRxiv preprint DOI: https://doi.org/10.1101/2020.03.05.20031815.  Back to cited text no. 50
    
51.
WHO. Coronavirus Disease 2019 (COVID-19) Situation Report –77. Data as Reported by National Authorities by 10:00CET6; April, 2020. Available from: https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200406-sitrep-77-covid-19.pdf?sfvrsn=21d1e632_2. [Last accessed on 2020 May 30].  Back to cited text no. 51
    
52.
Stadnytskyi V, Bax CE, Bax A, Anfinrud P. The airborne lifetime of small speech droplets and their potential importance in SARS-CoV-2 transmission. Proc Natl Acad Sci U S A 2020;117:11875-7.  Back to cited text no. 52
    
53.
DeMuri GP, Wald ER. The group a streptococcal carrier state reviewed: Still an enigma. J Pediatric Infect Dis Soc 2014;3:336-42.  Back to cited text no. 53
    
54.
van Belkum A. Hidden Staphylococcus aureus carriage: Overrated or underappreciated? MBio 2016;7:E00079-16.  Back to cited text no. 54
    
55.
Shenoy ES, Paras ML, Noubary F, Walensky RP, Hooper DC. Natural history of colonization with methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE): A systematic review. BMC Infect Dis 2014;14:177.  Back to cited text no. 55
    
56.
Gerding DN, Muto CA, Owens RC Jr. Measures to control and prevent Clostridium difficile infection. Clin Infect Dis 2008;46 Suppl 1:S43-9.  Back to cited text no. 56
    
57.
Bellan SE, Pulliam JR, Dushoff J, Meyers LA. Ebola control: Effect of asymptomatic infection and acquired immunity. Lancet 2014;384:1499-500.  Back to cited text no. 57
    
58.
Arreaza L, de La Fuente L, Vázquez JA. Antibiotic susceptibility patterns of Neisseria meningitidis isolates from patients and asymptomatic carriers. Antimicrob Agents Chemother 2000;44:1705-7.  Back to cited text no. 58
    
59.
Chen I, Clarke SE, Gosling R, Hamainza B, Killeen G, Magill A, et al. “Asymptomatic” Malaria: A Chronic and Debilitating Infection That Should Be Treated. PLoS Med 2016;13:e1001942.  Back to cited text no. 59
    
60.
Kimbrough W. The Importance of Testing Asymptomatic Patients for COVID-19; 7 May, 2020. Available from: https://www.onemedical.com/blog/live-well/asymptomatic-covid-19. [Last accessed on 2020 May 26].  Back to cited text no. 60
    
61.
CDC. Use of Cloth Face Coverings to Help Slow the Spread of COVID-19; 3 April, 2020. Available from: https://www.cdc.gov/coronavirus/2019 -ncov/prevent -getting-sick/cloth -face-cover.html. [Last accessed on 2020 May 26].  Back to cited text no. 61
    
62.
Hu Z, Song C, Xu C, Jin G, Chen Y, Xu X, et al. Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing, China. Sci China Life Sci 2020;63:706-11.  Back to cited text no. 62
    
63.
Gossner O. Group Testing Against COVID-19, Working Papers 2020-02, Center for Research in Economics and Statistics; 2020. Available from: https://ideas.repec.org/p/crs/wpaper/2020-02.html. [Last accessed on 2020 May 26].  Back to cited text no. 63
    
64.
Sinnott-Armstrong N, Klein D, Hickey B. Evaluation of Group Testing for SARS-CoV-2 RNA. medRxiv 2020. medRxiv preprint DOI: https://doi.org/10.1101/2020.03.27.20043968.  Back to cited text no. 64
    
65.
Zhang W, Long Q, Huang Y, Chen C, Wu J, Hong Y, et al. Asymptomatic COVID-19 have longer treatment cycle than moderate type of confirmed patients. medRxiv 2020. medRxiv preprint DOI: https://doi.org/10.1101/2020.05.16.20103796.  Back to cited text no. 65
    



This article has been cited by
1 Knowledge, Attitude and Practices Regarding “Reverse Quarantine” during COVID 19 Pandemic among Senior Citizens in an Urban Area of Kerala – A Longitudinal Study
Meera Karunakaran, Jayasree Chandrasekharan Nair Saradamma
Journal of Evolution of Medical and Dental Sciences. 2021; 10(45): 3920
[Pubmed] | [DOI]



 

Top
 
 
  Search
 
Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
Access Statistics
Email Alert *
Add to My List *
* Registration required (free)

 
  In this article
Abstract
Introduction
Search Strategy
Study Rationale
Classification a...
Sites of Carriag...
Magnitude of Asy...
Detection of Car...
Importance of Ca...
Prevention and C...
Conclusions
References

 Article Access Statistics
    Viewed5662    
    Printed228    
    Emailed0    
    PDF Downloaded444    
    Comments [Add]    
    Cited by others 1    

Recommend this journal