Resumo:
Background: Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is
the cause of Coronavirus Disease 2019 (COVID-19). Although Real Time Reverse
Transcription Polymerase Chain Reaction (qRT-PCR) of respiratory specimens is the
reference standard test for detection of SARS-CoV-2 infection, collecting
nasopharyngeal swabs (NPS) and/or oropharyngeal swabs (OPS) causes discomfort
to patients and may represent a considerable risk for healthcare workers. The use of
saliva as a diagnostic sample has several advantages. Objectives: The aim of this
study is to validate the use of saliva as a biological sample for diagnosis of COVID-19
and to evaluate the test performance of the Xpert Xpress SARS-CoV-2 cartridge
assay in comparison to a conventional qRT-PCR testing, using saliva as biological
specimen. Method: This study was developed at Complexo Hospitalar Professor
Edgard Santos (C-HUPES), in Salvador, Brazil. Participants presenting with
signs/symptoms suggesting SARS-CoV-2 infection, underwent a NPS and/or OPS,
and self-saliva collection. Saliva samples were diluted, RNA isolation and qRT-PCR
were performed. Results of conventional versus saliva samples testing were
compared. Saliva samples were used to validate the Xpert Xpress SARS-CoV-2
platform. Statistical analyses were performed using Statistical Package for the Social
Sciences software (SPSS) version 18.0. Descriptive statistics, Fisher and MannWhitney tests were performed; kappa coefficient, and coefficient of determination and
correlation were calculated. Results: One hundred fifty-five participants were
recruited, and samples pairs of NPS/OPS and saliva were collected. The sensitivity
and specificity of RT-PCR using saliva samples were 94.4% (95% CI 86.4 – 97.8)
and 97.6% (95% CI 91.7 – 99.3), respectively. The accuracy of the test using saliva
was 96.1%. Forty saliva samples from symptomatic participants were collected. In
the Xpert Xpress assay, the median cycle threshold value of the E gene was 29.7,
and of the N2 gene was 31.6. In the conventional assay, the median cycle threshold
value of the E gene was 34.9, and of the RdRp gene was 38.3. The correlation
between Xpert Xpress platform genes was 98%; between conventional PCR genes
was 86%; and between E gene from the two assays was 78%. Conclusions: The
use of self-collected saliva samples is an easy, convenient, and low-cost alternative
to conventional NP swab-based molecular tests. These results can allow a broaden
use of molecular tests for management of COVID19 pandemic, especially in
resources-limited settings.
