Saliva and Gargle vs Nasopharyngeal Samples for the Detection of COVID-19

Both saliva and gargle samples were effective for the detection of SARS-CoV-2 infection via reverse transcription polymerase chain reaction (RT-PCR) assay, and the detection rate with saliva was increased compared gargle samples and similar to nasopharyngeal samples. These findings were published in Diagnostic Microbiology and Infectious Disease.

In this meta-analysis, researchers sought to evaluate both saliva and gargle samples as potential alternatives nasopharyngeal samples for the detection of SARS-CoV-2 infection via reverse transcription polymerase chain reaction (RT-PCR) testing. Nasopharyngeal, saliva, and gargle samples were obtained from a cohort of 229 health care workers (HCW).

Study participants were working at a tertiary public hospital in Curitiba, Brazil between August 2020 and November 2020 and had been referred for SARS-CoV-2 testing due to either symptoms suggestive of COVID-19 infection or recent exposure. Three samples were collected sequentially from each participant, including nasopharyngeal samples obtained via viral transport medium, saliva samples via whole oral fluid, and gargle samples via saline gargle.

Among a total of 229 participants included in the final analysis, 177 (77%) reported symptoms, 35 (15%) were asymptomatic, and 17 did not report symptom data. Of patients diagnosed with COVID-19 infection, 41 (17.9%) tested positive via nasopharyngeal samples, 36 (87.8%) tested positive via saliva samples, and 33 (80.5%) tested positive via gargle samples. After the inclusion of patients in whom only the nucleocapsid (N) gene was detected, the number of patients with SARS-CoV-2 detected via saliva and gargle samples increased to 40 (97.6%) and 36 (92.7%), respectively.

Saliva and gargle samples were both compared against nasopharyngeal samples to estimate the sensitivity, specificity, and accuracy of RT-PCR associated with each type of sample. The kappa index for nasopharyngeal swabs vs both saliva and gargle samples was 0.89 and 0.84, respectively. The sensitivity, specificity and accuracy of saliva samples were 87.80%, 98.94%, and 96.94%, respectively. For gargle samples, sensitivity was 80.49%, specificity was 98.94%, and accuracy was 95.63%.

Limitations included differences in extraction methods and amplification kits used in the included in studies, and some patients did not provide all 3 types of samples. In addition, potential confounding may have occurred due to the time between sample collection and symptom onset.

According to the researchers, “since saliva can be self-collected, it may prove to be a substitute for SARS-CoV-2 surveillance, particularly in home environments, to test individuals in quarantine.” They also noted other advantages of saliva samples, including a decreased risk for COVID-19 exposure in HCWs, and a decreased need to use swabs and personal protective equipment.

Reference

Genelhoud G, Adamoski D, Nogueira Spalanzani R, et al. Comparison of SARS-CoV-2 molecular detection in nasopharyngeal swab, saliva, and gargle samples. Diagn Microbiol Infect Dis. Published online March 10, 2022. doi: 10.1016/j.diagmicrobio.2022.115678