|Year : 2021 | Volume
| Issue : 1 | Page : 54-66
Saliva as a Potential SARS-CoV-2 Reservoir: What is Already Known? A Systematic Review
Luciana Munhoz, Denise S Haddad, Emiko S Arita
Department of Stomatology, School of Dentistry, University of São Paulo, São Paulo, SP, Brazil
|Date of Submission||11-Apr-2021|
|Date of Decision||06-Jun-2021|
|Date of Acceptance||07-Jun-2021|
|Date of Web Publication||06-Aug-2021|
Department of Stomatology, School of Dentistry, University of São Paulo, 2227 Lineu Prestes Avenue, São Paulo, SP 05508-000
Source of Support: None, Conflict of Interest: None
Introduction: Saliva is a reservoir for biologic indicators and has a diverse microflora, which is critical particularly for coronavirus disease 2019 (COVID-19) transmission. Notwithstanding, saliva also could be applied as a noninvasive method to COVID-19 diagnosis and disease evolution monitoring. The objective of this systematic review is to summarize the main findings regarding to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection repercussion in saliva and/or salivary glands, addressing the following questions: What has been published regarding to the presence and implications of COVID-19 in saliva or salivary glands? and What are the researchers’ main results and conclusions?. Materials and Methods: A total of 31 published articles were included (27 research articles and 4 case reports). PubMed, Embase, Scopus, Web of Science, and Google Scholar databases were searched till August 2020. The terms COVID-19, novel coronavirus, and SARS-CoV-2 were combined with the keywords salivary gland, saliva, sialadenitis, parotid gland, sublingual gland submandibular gland, salivary gland disease, and minor salivary gland using the Boolean operator “AND.” Results: In this study, researchers’ main results and conclusions were exposed in tables. The main subjects of the articles were detection and viral load of SARS-CoV-2 in saliva, the influence of mouthwashes in SARS-CoV-2, and the presence of SARS-CoV-2 in aerosols. Conclusion: Although deep throat saliva may be used as a diagnostic tool to SAR-CoV-2 diagnosis, researchers found that the viral load in saliva is lower than in respiratory secretions.
Keywords: Dentistry, respiratory tract infections, saliva, salivary glands
|How to cite this article:|
Munhoz L, Haddad DS, Arita ES. Saliva as a Potential SARS-CoV-2 Reservoir: What is Already Known? A Systematic Review. J Orofac Sci 2021;13:54-66
|How to cite this URL:|
Munhoz L, Haddad DS, Arita ES. Saliva as a Potential SARS-CoV-2 Reservoir: What is Already Known? A Systematic Review. J Orofac Sci [serial online] 2021 [cited 2021 Nov 30];13:54-66. Available from: https://www.jofs.in/text.asp?2021/13/1/54/323359
| Introduction|| |
Coronaviruses are large, enveloped, RNA viruses, with a unique microscopic morphology of spherical virions with a core shell and surface projections, hence resembling a solar corona. Coronaviruses infect a wide range of animals, including humans, and have four distinct subclassifications, namely alpha-, beta-, gamma-, and delta-coronaviruses. Alpha- and beta-coronaviruses originate from mammals, particularly bats. The current novel human coronavirus, which was first described in 2019, is derived from the B-lineage of a beta-coronavirus and is now referred to as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). As human SARS-CoV-2 is almost identical to the bat coronavirus (96% identical at the whole-genome level), it is hypothesized that the virus had succeeded in making its transition from bats to humans; however, the precise route of transmission is still unclear.
Saliva is an exocrine secretion which contains a complex mixture of components, such as water, electrolytes, and organic proteins, as amylase, mucin, urea, cholesterol glucose, peroxidase, lysozyme, cortisol, immunoglobulin, and other glycoproteins. A variety of antigens can be detected in saliva, as well as the presence of viral ribonucleic acid, which leads to a diverse application of saliva as a diagnostic tool for viral diseases. On the other hand, saliva is also pointed as a fluid that plays a crucial hole in the transmission of viral diseases.
Dental professionals work directly in the oral cavity and are vulnerable to contamination from the saliva of patients, which contains secretions from the nasopharynx and lung via the action of cilia lining the airways. Saliva is established as a reservoir for biologic indicators such as nucleic acids, proteins, and a widely diverse microflora, as well as viruses such as SARS-CoV-2. As a diagnostic fluid, saliva has an advantage over other biologic fluids as its sampling process is not invasive or expensive.
Thus, considering the importance of saliva as a potential virus carrier and its role in patient-to-professional contamination during dental treatments, as well as its capability to be applied as a diagnostic tool for coronavirus disease 2019 (COVID-19), the present systematic review intent to address the following questions: 1. What has been published regarding to the presence and implications of COVID-19 in saliva or salivary glands? 2. What are the researchers’ main results and conclusions?
| Materials and Methods|| |
Protocol and registration
This systematic review was registered at the National Institute for Health Research PROSPERO International Prospective Register of Systematic Reviews (registration number CRD42020192238). The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist was followed.
The identification of the studies eligible for inclusion in this literature review was performed using the PubMed, Embase (Excerpta Medica Database), Scopus, Web of Science, and Google Scholar databases. The aforementioned databases were searched until August 2020, using Medical Subject Headings (MeSH) terms as keywords. As the novel coronavirus infection was not already added as a medical subject heading, the names COVID-19, novel coronavirus, and SARS-CoV-2 were applied. The Boolean operator “AND” was applied to combine the searches. Itemized search strategies were established for each database, and they were based on the following search strategies: salivary gland AND covid-19, saliva AND covid-19, sialadenitis AND covid-19, parotid gland AND covid-19, sublingual gland AND covid-19, submandibular gland AND Covid-19, salivary gland disease AND covid-19, minor salivary gland AND covid-19, salivary gland AND Novel coronavirus, saliva AND Novel coronavirus, sialadenitis AND Novel coronavirus, parotid gland AND Novel coronavirus, sublingual gland AND Novel coronavirus, submandibular gland AND Novel coronavirus, salivary gland disease AND Novel coronavirus, minor salivary gland AND Novel coronavirus, salivary gland AND SARS-CoV-2, saliva AND SARS-CoV-2, sialadenitis AND SARS-CoV-2, parotid gland AND SARS-CoV-2, sublingual gland AND SARS- CoV-2, submandibular gland AND SARS-CoV-2, salivary gland disease AND SARS-CoV-2, minor salivary gland AND SARS-CoV-2.
Types of studies
Original studies and case reports were considered appropriate for inclusion. Literature reviews, comments, short communications, technical notes, and preprint articles (without peer review) were not considered eligible. Additionally, non-English language studies and investigations involving animals exclusively were excluded. In case of impossibility to read the full text of the published article, the study was excluded.
Participant groups or samples with confirmed COVID-19 were included in the data selection. Liquid matrices that simulated saliva were also considered appropriate for inclusion.
The data extraction was executed by three independent reviewers. The reviewers initially screened the titles and abstracts, using the previously elected keywords, and then reviewers verified the full text to choose acceptable investigations. Disagreements between the reviewers were solved by discussion and, when an understanding could not be reached, a collaborator was consulted.
Study data were extracted, summarized, and organized, as follows: author information, publication month and year, researcher country of affiliation, study objective, methodology applied, number of participants or samples evaluated, main results, and conclusions.
Data analyses − risk of bias
The search results were organized and summarized in one flow chart, according to PRISMA statement [[Figure 1]–data selection] and [Table 1] and [Table 2].
|Figure 1 Flow chart summarizing the data search, according to PRISMA statement. *COVID-19-related words: COVID-19; novel coronavirus; SARS-CoV-2.|
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|Table 1 Publication details of the 31 included articles: year and month of the publication, country of origin, type of study (original article or case report), and main objective|
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|Table 2 Risk of bias assessment evaluated by the non-randomized studies of interventions (Robins-I) tool|
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The quality of each original research was assessed using the Cochrane risk of bias tool for nonrandomized studies [Table 3], and case reports were assessed by Joanna Briggs Institute tool [Table 4].
|Table 3 Assessment of case reports according to the Joanna Briggs Institute tool|
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|Table 4 Summaries of the 31 included articles: methods, number of patients or samples included, main results and conclusions pertaining to saliva and/or salivary glands|
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| Results|| |
A total of 17,290 articles were searched and 31,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, were considered eligible for inclusion. [Table 1], demonstrates selected article data (month and year of publication, country of author’s institution, and article objective). Twenty-seven were research articles,,,, and 4 were case reports. ,,,
The subject of the articles selected were: SARS-CoV-2 detection in saliva,,,,; SARS-CoV-2 detection in posterior oropharyngeal saliva samples ,, or buccal swabs,; patient saliva self-collection and testing,,; distribution of angiotensin‐converting enzyme 2 and transmembrane serine proteases 2 in salivary glands,,; SARS-CoV-2 detection in samples from surgical resection of tongue squamous cell carcinoma; comparisons with oropharyngeal and nasopharyngeal swabs for testing,,,; development of a rapid test using saliva; virucidal activity of different available oral rinses; the use of trained dogs in the detection of SARS-CoV-2 in the saliva of infected patients; correlation between saliva tests and patient clinical data or patient symptoms,; the influence sunlight and humidity on SARS-CoV-2 in aerosols; and the presence of the virus in the gingival fluid.
The risk of bias assessment for the research articles selected according to Robins-I tool (for nonrandomized studies of interventions) is summarized in [Table 2].
Regarding the case report subjects, there was a description on detection of SARS-CoV-2 in saliva of a patient 37 days after the disease onset, the description of a case on detection of SARS-CoV-2 when performing histologic examination of a tongue malignant neoplasm, and the characterization of patients with SARS-CoV-2 who presented with parotitis as the first sign of the disease., The risk of bias assessment for the case reports, according to Joanna Briggs Institute tool, is summarized in [Table 3].
The methods, number of participants or samples of each investigation, main results, and conclusions pertaining to saliva and/or salivary glands and related subjects are presented in [Table 4].
| Discussion|| |
Since the identification of SARS-CoV-2 in Wuhan, China, and its rapid spread worldwide, a broad spectrum of disease severity and symptoms has been reported. The main clinical manifestations of COVID-19 are fever, cough, and fatigue, similar to that of other coronavirus infections, as well as seasonal influenza. However, asymptomatic patients can also transmit the virus, which complicates the detection of infected individuals.
Pneumonia is the main complication in infected symptomatic individuals, but acute respiratory syndrome, acute kidney injury, sepsis, and death have also been observed. Low rates of death (approximately 3.2–4.3%) associated with SARS-CoV-2 have been reported., Risk factors for poorer outcomes include old age and comorbidities, such as diabetes or autoimmune diseases.
The SARS-CoV-2 has rapid transmissibility, and asymptomatic virus carriers may also transmit the virus to other individuals, including healthcare professionals.  The transmission of SARS-CoV-2 is no different from any other respiratory virus and may occur via saliva droplets from talking, coughing, and sneezing. Infection can also result from physical contact with contaminated surfaces containing saliva or blood droplets from of an infected person.
The presence of SARS-CoV-2 has been reported in the saliva of over 90% of symptomatic and asymptomatic infected patients., Moreover, the SARS-CoV-2 infection affects directly salivary glands, leading to symptoms such as dry mouth, amblygeustia, taste loss, and eventually parotiditis,, which is a response to the hyperinflammatory response to SARS-CoV-2.
Considering the aforementioned, most of the researchers focused in verifying if saliva could be used as a diagnostic tool for SARS-CoV-2, comparing salivary samples collection with other respiratory specimens.,,,,,,,, Investigators reported promising results, verifying that salivary samples had similar,,,,,, or better, performance in detecting SARS-CoV-2 when compared with conventional respiratory specimens. However, Kam et al. reported poorer sensitivity of buccal swabs when compared with nasopharyngeal swabs from symptomatic and asymptomatic children, emphasizing that the viral load were substantially lower in buccal swabs.
Regarding the viral load in salivary samples, it was observed that the viral load of SARS-CoV-2 was lower in salivary specimens when compared with nasopharyngeal specimens. Additionally, salivary viral load during the first week after symptomatology onset and in older age patients was positively correlated with higher viral load, and viral load was more expressive in the early morning saliva. Although viral load can differ according to age or disease evolution, quantitative viral detection could not be fully correlated with clinical symptomatology.
Furthermore, salivary sample self-collection was cited as a safe alternative diagnostic examination for SARS-CoV-2,, with should be used to avoid health system overburden. Additionally, new fast and cheaper tests using saliva, similar than the investigated by Samavati et al., which is probe that detect the virus in any stage of the disease, must be deeply investigated and are promising technologies. Nevertheless, saliva collection methodology needs to be improved before applied in extensive testing.
The presence and behavior of SARS-CoV-2 in aerosols were investigated by Schuit et al. which used aerosol chambers with controlled temperature, relative humidity, and simulated sunlight. Researchers verified that sunlight exposure leads to virus decay, but temperature and relative humidity did not influence significantly virus persistence in aerosols.
In this context, dental professionals should be particularly aware of the aerosols generated during clinical procedures and on contaminated tools or surfaces. As dental equipment, such as high-speed dental turbines, ultrasonic scalers, and air–water syringes, produce a large quantity of aerosols that mix with saliva and other particles that may contain microorganisms such as SARS-CoV-2, dentists and other dental health care professionals are particularly vulnerable to coronavirus infections.
The use of oral rinses before dental procedures may diminish, but not eliminate, viral load and, as a result, patient-to-professional contamination. Yoon et al. noticed that chlorhexidine mouthwash was effective in reducing SARS-CoV-2 viral load in saliva; Meister et al. verified that mouthwashes containing dequalinium chloride associated to benzalkonium chloride, polyvidone-iodine, and ethanol associated to essential oils also reduces virus infectivity within short exposure time (30 seconds).
| Conclusion|| |
The main publications available in literature regarding to the implications of COVID-19 in saliva are associated to the detection of SARS-CoV-2 in saliva, SARS-CoV-2 viral load in saliva, the effects of mouthwash in SARS-CoV-2, and the presence of the virus in aerosols. Although deep throat saliva may be used as a diagnostic tool to SAR-CoV-2 diagnosis, researchers found that the viral load in saliva is lower than in respiratory secretions. However, it is necessary to emphasize that the information presented in this review represents the best of authors’ knowledge at the time of data collection, as researchers related to SARS-CoV-2 have been developing quickly.
The limitation of the present review is the ever changing evidence that may rapidly outdated the information discussed in this review.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Velavan TP, Meyer CG. The COVID-19 epidemic. Trop Med Int Health 2020;25:278-80.
Zhou P, Yang XL, Wang XG et al.
A pneumonia outbreak associated with a new coronavirus of probable bat origin. Nature 2020;579:270-3.
To KK, Tsang OT, Chik-Yan Yip C et al.
Consistent detection of 2019 novel coronavirus in saliva. Clin Infect Dis 2020;71:841-3.
Baghizadeh Fini M. Oral saliva and COVID-19. Oral Oncol 2020;108:104821.
Knobloch K, Yoon U, Vogt PM. Preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement and publication bias. J Craniomaxillofac Surg 2011;39:91-2.
Sterne JAC HM, McAleenan A, Reeves BC, Higgins JPT. Chapter 25: Assessing risk of bias in a non-randomized study. In Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA, eds. Cochrane Handbook for Systematic Reviews of Interventions, version 6.0 (updatedJuly 2019). Cochrane, 2019. Available at www.training.cochrane.org/handbook.2019
Huang N, Pérez P, Kato T et al.
SARS-CoV-2 infection of the oral cavity and saliva. Nat Med. 2021;27:892-903.
Gupta S, Mohindra R, Chauhan PK et al.
SARS-CoV-2 detection in gingival crevicular fluid. J Dent Res 2021;100:187-93.
Sakanashi D, Asai N, Nakamura A et al.
Comparative evaluation of nasopharyngeal swab and saliva specimens for the molecular detection of SARS-CoV-2 RNA in Japanese patients with COVID-19. J Infect Chemother 2021;27:126-9.
Braz-Silva PH, Mamana AC, Romano CM et al.
Performance of at-home self-collected saliva and nasal-oropharyngeal swabs in the surveillance of COVID-19. J Oral Microbiol 2020;13:1858002.
Chen L, Zhao J, Peng J et al.
Detection of SARS-CoV-2 in saliva and characterization of oral symptoms in COVID-19 patients. Cell Prolif 2020;53:e12923.
Chern A, Famuyide AO, Moonis G, Lalwani AK. Sialadenitis: a possible early manifestation of COVID-19. Laryngoscope 2020;130:2595-7.
Samavati A, Samavati Z, Velashjerdi M et al.
Sustainable and fast saliva-based COVID-19 virus diagnosis kit using a novel GO-decorated Au/FBG sensor. Chem Eng J 2020:127655.
Hanege FM, Kocoglu E, Kalcioglu MT et al.
SARS-CoV-2 presence in the saliva, tears, and cerumen of COVID-19 patients. Laryngoscope 2021;131:E1677-82.
Senok A, Alsuwaidi H, Atrah Y et al.
Saliva as an alternative specimen for molecular COVID-19 testing in community settings and population-based screening. Infect Drug Resist 2020;13:3393-9.
Lechien JR, Chetrit A, Chekkoury-Idrissi Y et al.
Parotitis-like symptoms associated with COVID-19, France, March–April 2020. Emerg Infect Dis. 2020;26:2270-1.
Güçlü E, Koroglu M, Yürümez Y et al.
Comparison of saliva and oro-nasopharyngeal swab sample in the molecular diagnosis of COVID-19. Rev Assoc Med Bras (1992). 2020;66:1116-21.
Lai CKC, Chen Z, Lui G et al.
Prospective study comparing deep-throat saliva with other respiratory tract specimens in the diagnosis of novel coronavirus disease (COVID-19). J Infect Dis 2020;222:1612-9.
Landry ML, Criscuolo J, Peaper DR. Challenges in use of saliva for detection of SARS CoV-2 RNA in symptomatic outpatients. J Clin Virol 2020;130:104567.
Rao M, Rashid FA, Sabri FSAH et al.
Comparing nasopharyngeal swab and early morning saliva for the identification of SARS-CoV-2. Clin Infect Dis. 2021;72:e352-6.
Schuit M, Ratnesar-Shumate S, Yolitz J et al.
Airborne SARS-CoV-2 is rapidly inactivated by simulated sunlight. J Infect Dis 2020;222:564-71.
Vaz SN, Santana DS, Netto EM et al.
Saliva is a reliable, non-invasive specimen for SARS-CoV-2 detection. Braz J Infect Dis 2020;24:422-7.
Azzi L, Carcano G, Gianfagna F et al.
Saliva is a reliable tool to detect SARS-CoV-2. J Infect 2020;81:e45-50.
Jendrny P, Schulz C, Twele F et al.
Scent dog identification of samples from COVID-19 patients − a pilot study. BMC Infect Dis 2020;20:536.
Leung EC, Chow VC, Lee MK, Lai RW. Deep throat saliva as an alternative diagnostic specimen type for the detection of SARS-CoV-2. J Med Virol 2020;93:533-6.
Meister TL, Brüggemann Y, Todt D et al.
Virucidal efficacy of different oral rinses against SARS-CoV-2. J Infect Dis 2020;14;222:1289-92.
Cheuk S, Wong Y, Tse H et al.
Posterior oropharyngeal saliva for the detection of SARS-CoV-2. Clin Infect Dis 2020;31;71:2939-46.
Kam KQ, Yung CF, Maiwald M et al.
Clinical utility of buccal swabs for SARS-CoV-2 detection in COVID-19-infected children. J Pediatric Infect Dis Soc 2020;9:370-2.
Lamb LE, Bartolone SN, Ward E, Chancellor MB. Rapid detection of novel coronavirus/severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by reverse transcription-loop-mediated isothermal amplification. PLoS One 2020;15:e0234682.
Tajima Y, Suda Y, Yano K. A case report of SARS-CoV-2 confirmed in saliva specimens up to 37 days after onset: proposal of saliva specimens for COVID-19 diagnosis and virus monitoring. J Infect Chemother 2020;26:1086-9.
Chen JH, Yip CC, Poon RW et al.
Evaluating the use of posterior oropharyngeal saliva in a point-of-care assay for the detection of SARS-CoV-2. Emerg Microbes Infect 2020;9:1356-9.
Guerini-Rocco E, Taormina SV, Vacirca D et al.
SARS-CoV-2 detection in formalin-fixed paraffin-embedded tissue specimens from surgical resection of tongue squamous cell carcinoma. J Clin Pathol 2020;73:754-7.
Pasomsub E, Watcharananan SP, Boonyawat K et al.
Saliva sample as a non-invasive specimen for the diagnosis of coronavirus disease 2019: a cross-sectional study. Clin Microbiol Infect 2020;27:285.e1-285.e4.
Song J, Li Y, Huang X, Chen Z, Liu C, Duan X. Systematic analysis of ACE2 and TMPRSS2 expression in salivary glands reveals underlying transmission mechanism caused by SARS-CoV-2. J Med Virol 2020;92:2556-66.
To KK, Tsang OT, Leung WS et al.
Temporal profiles of viral load in posterior oropharyngeal saliva samples and serum antibody responses during infection by SARS-CoV-2: an observational cohort study. Lancet Infect Dis 2020;20:565-74.
Yoon JG, Yoon J, Song JY et al.
Clinical significance of a high SARS-CoV-2 viral load in the saliva. J Korean Med Sci 2020;35:e195.
Sullivan PS, Sailey C, Guest JL et al.
Detection of SARS-CoV-2 RNA and antibodies in diverse samples: protocol to validate the sufficiency of provider-observed, home-collected blood, saliva, and oropharyngeal samples. JMIR Public Health Surveill 2020;6:e19054.
Guan WJ, Ni ZY, Hu Y et al.
Clinical characteristics of coronavirus disease2019 in China. N Engl J Med 2020;382:1708-20.
Wang D, Hu B, Hu C et al.
Clinical characteristics of 138 hospitalized patients with2019 novel coronavirus-infected pneumonia in Wuhan, China. JAMA 2020;323:1061-9.
Bai Y, Yao L, Wei T et al.
Presumed asymptomatic carrier transmission of COVID-19. JAMA 2020;323:1406-7.
Sabino-Silva R, Jardim ACG, Siqueira WL. Coronavirus COVID-19 impacts to dentistry and potential salivary diagnosis. Clin Oral Investig 2020;4:1619-21.
Gherlone EF, Polizzi E, Tetè G et al.
Frequent and persistent salivary gland ectasia and oral disease after COVID-19. J Dent Res 2021;100:464-71.
[Table 1], [Table 2], [Table 3], [Table 4]