Posterior Oropharyngeal Saliva for the Detection of SARS-CoV-2
Main result
Inclusion of 229 pairs of posterior-nasopharyngeal oropharyngeal salivary samples from 95 patients, of which 57 confirmed for COVID-19. The median age of the patients was 36 years and 57% were male.
The median time between two samplings was 42 minutes (ranging from 0 minutes to 21h).
70% of nasopharyngeal swabs were performed.
Sample positivity rates (out of 229 pairs):
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- posterior oropharyngeal salivary sampling: 61.6% (95% CI: 55.1% - 67.6%)
- nasopharyngeal sampling: 53.3% (95% CI: 46.8% - 59.6%)
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Percentage of positive agreement between the two types of samples: 85.2% (95% CI: 77.4% - 90.8%)<P> Percentage of negative agreement between the two types of samples: 65.4% (95% CI: 55.5% - 74.2%)<P> Percentage of overall agreement: 76.0% (95% CI: 70.2% - 80.9%), Cohen's kappa coefficient reflecting moderate agreement between the results of the two types of samples: 0.512 (95% CI: 0.401 - 0.623).
Among the positive pairs, the difference in process capacity (Cp) between the two types of samples is in favor of nasopharyngeal samples.
Among symptomatic patients with confirmed COVID-19 (44 subjects and 161 pairs of samples), the percentage of positive agreement between the two types of samples is best when the sample is taken within 7 days of the onset of symptoms.
Among the discordant pairs, posterior oropharyngeal salivary sampling was more frequently associated with SARS-CoV-2.
Takeaways
Strength of evidence Weak
- retrospective collection of data
- inclusion of suspected but unconfirmed COVID-19 patients
- adherence to posterior oropharyngeal saliva sampling guidelines for only 56% of samples
- insufficient number of children to analyze the performance of posterior oropharyngeal saliva sampling in pediatrics
- heterogeneity of nasopharyngeal sampling types does not rule out the existence of better results for a particular method
- non-systematic addition of viral transport medium in posterior oropharyngeal saliva samples
- lack of clear definition of process capacity (Cp)
Objectives
Method
Result comparison from a pair of oropharyngeal-nasopharyngeal samples collected the same day in the same patient:
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- Posterior oropharyngeal salivary: collection according to standardized instructions for the patients on how to scrape their throat in a sterile container as soon as possible after rising and before eating, drinking or brushing their teeth.
- Nasopharyngeal swabbing or aspiration following nose blowing: performed by the medical staff followed by the addition of 1 ml of viral transport medium.
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If both samples were taken from the same patient, the posterior oropharyngeal saliva sample was always collected before the nasopharyngeal sample.
Samples were processed by the biology laboratory within 24 hours of collection.
Analysis of diagnostic performance, agreement between samples and temporal variation of result discrepancy.
Performance based on percentage agreement between methods in the absence of a gold standard established for the diagnosis of SARS-CoV-2 infection.
The number of samples required for the study was calculated in such a way that a difference between an actual kappa coefficient of 0.5 and a kappa coefficient of 0.7, with an alpha risk fixed at 0.05 and a potency fixed at 0.80 could be detected under the assumption of a positivity rate of 0.5 and 0.6 for oropharyngeal and nasopharyngeal samples respectively.
109 pairs of oropharyngeal-nasopharyngeal samples were included.
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