TABLE 1

Characteristics of included studies of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reverse transcriptase (RT)-PCR testing

Author (year) [ref.]Study periodLocationSettingPositivity rate of (O)NPS (95% CI), %Patient characteristicsCriteria for SARS-CoV-2 infectionSampling approachesGargling techniqueAge (years)Includes childrenTarget geneCycle thresholdPeer reviewedEvidence rating
Kandel et al. (2021) [28]28 August 2020–25 September 2020CanadaThree outpatient COVID-19 assessment centres10.53Suspected, symptomatic and asymptomatic outpatientsNANPS, 0.9% saline gargleSwish and gargle three times with 3 mL of 0.9% normal salineMedian: 33
IQR: 24–51
YesE, 5′UTR#, S, ORF1ab38#, 37YesModerate
Dumaresq et al. (2021) [57]8 October 2020–23 October 2020CanadaDrive-through test centre12.04Suspected, symptomatic and asymptomatic individualsNACombined ONPS, natural spring water gargleRinse the mouth with 5 mL of natural spring water for 5 s, tilt the head back and gargle for 5 s, repeat this cycle once, expel the water back in the plastic cup and empty it in a 15 mL conical polypropylene centrifuge tubeMedian: 40
Range: 6–91
YesRdRP, N, ENAYesHigh
Olearo et al. (2021) [49]1 December 2020–28 February 2021GermanyUniversity hospital3.45Asymptomatic HCWNANPS, tap water gargleGargle at home with 5–7 mL of tap water for 30 s, spit into an empty 10 mL sterile container using a straw, with instructions in flyers and videosNANoORF1ab, ENAYesModerate
Zander et al. (2021) [54]October, 2020–December, 2020GermanyDoctors' offices32.50Suspected mostly symptomatic outpatientsNANPS, saline gargle30 s gargling of 5 mL 0.9% NaClRange: 13–89YesE35YesHigh
Kocagoz et al. (2021) [55]NATurkeyHospital20.94Suspected symptomatic inpatientsNANPS, drinking water gargleTake a few sips of regular drinking water, gargle and rigorously rinse the mouth forcefully with drinking water for at least 10 s, spit into an empty cupRange: ≥18NoORF1abNAYesModerate
Benoit et al. (2021) [50]November 2020–December 2020CanadaTwo COVID-19 screening clinics20.03Suspected, symptomatic outpatients or asymptomatic close contactsNACombined ONPS, natural spring water gargleGargle with 5 mL of natural spring water for 5 s in the mouth, 5 s in the throat, to repeat the cycle once, then spit in the initial gobletNANAORF1ab, ENAYesHigh
Utama et al. (2022) [59]3 March 2021–19 July 2021IndonesiaHospital60.66Suspected symptomatic and asymptomatic outpatients; confirmed symptomatic and asymptomatic COVID-19 inpatients and SARS-CoV-2-negative inpatientsPreviously diagnosed COVID-19-positive and admitted to hospitals+Combined ONPS, gargle§Satisfy 45-min fasting period, deeply inhale 5–6 times, throat cough 5–6 times, gargle 2.5 mL of gargle solution, spit into a collection tube with 3 mL BioSaliva Collection Buffer, with instructions in the protocol, and supervised by HCWMean: 34.3±12.5 (outpatients); 45.4±16.5 (inpatients)YesHelicase, RdRP40YesModerate
Goldfarb et al. (2021) [47]8 May 2020–11 September 2020CanadaCOVID-19 collection centre and residence74.47Confirmed and suspected, symptomatic and asymptomatic COVID-19 outpatientsHad SARS-CoV-2 detected in any clinical sample within a median of 3 days from infection confirmation+NPS, sterile 0.9% saline gargleSwish 5 mL of sterile 0.9% saline in the mouths for 5 s followed by tilting the head back and gargling for 5 s. This gargle cycle was repeated two more times and the saline was expelled into a sterile empty containerRange: 4–71YesE, RdRp40YesModerate
Michel et al. (2021) [36]May 2020GermanyRefugee facility51.32Confirmed and suspected, asymptomatic individualsHad a previous positive PCR-test for SARS-CoV-2 at a median time of 14 days prior+Combined ONPS, sterile water gargleGargling for at least 5 s with 10 mL sterile water under the supervision of medical personnel; gargling was demonstrated if necessaryMean: 29
Range: 7–59
YesE, ORF1a40YesModerate
Guo et al. (2020) [46]23 March 2020–31 March 2020ChinaHospital4.17Confirmed COVID-19 hospitalised and discharged patientsLaboratory-confirmed COVID-19, met the diagnosis criteria of COVID-19 as per national guideline, within 48–57 days of symptom onsetNPS, sterile normal saline gargleOscillate over the posterior pharyngeal wall with 20 mL of sterile normal saline for 5–10 s, then spit out the saline into a sterile containerRange: 26–83NoN, ORF1abNAYesModerate
Poukka et al. (2021) [29]NAFinlandAcute COVID-19 outpatients95Confirmed symptomatic and asymptomatic COVID-19 outpatientsHad been diagnosed with SARS-CoV-2 infection by RT-PCR on NPS within 1–2 days of diagnosisNPS, water gargleGargle sip of water (1/4 of a glass) for 5–20 s before spitting it into a containerMean: 38.7±12.6
Range: ≥3
NAENAYesModerate
Gertler et al. (2021) [48]7 December 2020–11 January 2021GermanyUniversity hospital and residence100Confirmed symptomatic COVID-19 outpatientsInitial laboratory RT-PCR confirmation of SARS-CoV-2 by professional-collected, combined ONPS in a testing centre, enrolled within 2–15 days from symptom onsetCombined ONPS, tap water gargleGargle 10 mL tap water and spit into a plastic container; written instructions and observed without any additional verbal instructionsMedian: 31.5
Range: 17–66
YesE, ORF1abNAYesModerate
Mittal et al. (2020) [35]May 2020–June 2020IndiaTertiary care hospital100Confirmed symptomatic and asymptomatic COVID-19 inpatientsRT-PCR-confirmed patients with SARS-CoV-2 infection within 72 h of diagnosis by a trained HCW, as per the national and hospital policiesNPS, sterile normal saline garglePerform gargle with 8–10 mL sterile normal saline for 15–20 s and spit back to a screw-capped containerMean: 45.08±12.78NoN1, N240YesModerate
Kwon et al. (2022) [58]7 May 2021–7 July 2021KoreaMedical centres and hospital50.50Confirmed symptomatic and asymptomatic COVID-19 inpatients and healthy individualsPreviously confirmed COVID-19 patients hospitalised in medical centres and hospital+NPS, Bean extract gargleSwirl and gargle 5 mL of bean extract-based gargle for 2 min, spit into a tubeMean: 43.7, Range: 18–83NoRdRP, E, NNAYesModerate
Hitzenbichler et al. (2021) [51]27 April 2020–8 December 2020GermanyMedical centre85.29Confirmed symptomatic and asymptomatic COVID-19 inpatientsPatients with COVID-19 admitted to nonintensive care medical ward, with laboratory-confirmed SARS-CoV-2 infection (defined by a positive RT-qPCR result before inclusion)NPS, sterile saline or water gargleGargle 10 mL medical grade saline or water for 5–10 s, oscillating over the posterior pharyngeal wall, transfer the liquid into a sterile test tubeMean: 57.5±14.9, Range: 22–83NoENAYesModerate
Kinshella et al. (2021) [52]4 September 2020–29 October 2020CanadaHospital COVID-19 collection centre100Confirmed symptomatic COVID-19 outpatientsPatients with positive RT-PCR result of NPSNPS, sterile saline gargleSwish 5 mL of sterile 0.9% saline for 5 s, tilt the head back and gargle for 5 s. Repeat the swish and gargle cycle two more times, expel the saline into a sterile empty container. Saline gargle was self-collected with collection observed by nursing staff, or with written and visual collection instructions, but no observation and no guidance provided by an HCWMedian: 29.5
IQR: 14–41
YesE, RdRP40YesModerate
Biber et al. (2021) [53]July 2020–September 2020IsraelNonhospital facilities dedicated to COVID-19 patients in isolation84.67Confirmed symptomatic and asymptomatic COVID-19 outpatients in isolationCOVID-19 outpatients previously RT-PCR-confirmed by combined ONPSCombined ONPS, normal saline (0.9%) gargleRinse and gargle 10 cc (10 mL) of normal saline (0.9%) for 10–20 s, spit into a sterile containerRange: 18–73NoN, E, RdRP40YesHigh
Casati et al. (2022) [56]NAGermanyMedical university48.72Confirmed symptomatic COVID-19 ambulatory patients and negative close contactsPreviously tested positive for SARS-CoV-2 via RT-PCR on NPS+NPS, sterile saline garglePerform gargling with 8 mL of sterile 0.9% saline, and spit into a sterile container without additives, after verbal and visual instructionsNANAENAYesModerate

CI: confidence interval; COVID-19: coronavirus disease 2019; E: envelope gene; HCW: healthcare worker; IQR: interquartile range; ONPS: oropharyngeal–nasopharyngeal swab; ORF: open reading frame gene; N: nucleocapsid gene; NA: not available; NPS: nasopharyngeal swab; RdRP: RNA-dependent RNA polymerase gene; RT-qPCR: quantitative reverse transcription PCR; S: spike protein gene; UTR: untranslated region. Normal saline denotes 0.9% saline. #: for NPS only. : for gargle only. +: for confirmed cases only. §: no information on gargling medium.