ABSTRACT
BackgroundAirport quarantine is required to reduce the risk of entry of travelers infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, it is challenging for both high accuracy and rapid turn-around time to coexist in testing; polymerase chain reaction (PCR) is time-consuming with high accuracy, while antigen testing is rapid with less accuracy. Methods88,924 (93.2%) of 95,457 arrivals at three international airports in Japan were tested for SARS-CoV-2 using self-collected saliva by a screening strategy with initial chemiluminescent enzyme immunoassay (CLEIA) followed by confirmatory nucleic acid amplification tests (NAAT) only for intermediate range antigen concentrations. Results254 (0.27%) persons were found to be SARS-CoV-2 antigen positive ([≥] 4.0 pg/mL) by CLEIA. NAAT was required for confirmatory testing in 513 (0.54%) persons with intermediate antigen concentrations (0.67-4.0 pg/mL) whereby the virus was detected in 34 (6.6%) persons. This two-step strategy dramatically reduced the utilization of NAAT to approximately one out of every 200 test subjects. Estimated performance of this strategy did not show significant increase in false negatives as compared to performing NAAT in all subjects. Further reduction in imported cases may be achieved by post-screening quarantine. ConclusionsPoint of care testing by quantitative CLEIA using self-collected saliva is less labor-intensive and yields results rapidly, thus suitable as an initial screening test. Reserving NAAT for CLEIA indeterminate cases may prevent compromising accuracy while significantly improving the logistics of administering mass-screening at large venues.
ABSTRACT
COVID-19 is diagnosed by detecting SARS-CoV-2 by nasopharyngeal swab (NPS) using real-time quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). Emerging evidences have shown the utility of saliva, although conflicting results have been reported regarding viral loads between NPS and saliva. We conducted a study to compare the viral loads in 42 patients with COVID-19. Both NPS and saliva specimens were simultaneously obtained at a median of 6 days (range, 1-12) after symptom onset. SARS-CoV-2 was detected in 34 (81%) using NPS (median Ct value [IQR]=27.4 [21.3, 35.6]) and 38 (90%) using saliva (median Ct value [IQR]= 28.9 [23.1, 33.6]). There was no significance difference between them (Wilcoxon signed rank test: P=0.79) and Kendalls W was 0.82, showing a high degree of agreement, indicating equivalent viral loads in NPS and saliva. After symptom onset, the Ct values of both NPS and saliva continued to increase over time, with no substantial difference. Self-collected saliva has a detection sensitivity comparable to that of NPS and is a useful diagnostic tool with mitigating uncomfortable process and the risk of aerosol transmission to healthcare workers.
ABSTRACT
BackgroundCOVID-19 has rapidly evolved to become a global pandemic due largely to the transmission of its causative virus through asymptomatic carriers. Detection of SARS-CoV-2 in asymptomatic people is an urgent priority for the prevention and containment of disease outbreaks in communities. However, few data are available in asymptomatic persons regarding the accuracy of PCR testing. Additionally, although self-collected saliva has significant logistical advantages in mass screening, its utility as an alternative specimen in asymptomatic persons is yet to be determined. MethodsWe conducted a mass-screening study to compare the utility of nucleic acid amplification, such as reverse transcriptase polymerase chain reaction (RT-PCR) testing, using NPS and saliva samples from each individual in two cohorts of asymptomatic persons: the contact tracing cohort and the airport quarantine cohort. ResultsIn this mass-screening study including 1,924 individuals, the sensitivity of nucleic acid amplification testing with nasopharyngeal and saliva specimens were 86% (90%CI:77-93%) and 92% (90%CI:83-97%), respectively, with specificities greater than 99.9%. The true concordance probability between the nasopharyngeal and saliva tests was estimated at 0.998 (90%CI:0.996-0.999) on the estimated airport prevalence, 0.3%. In positive individuals, viral load was highly correlated between NPS and saliva. ConclusionBoth nasopharyngeal and saliva specimens had high sensitivity and specificity. Self-collected saliva is a valuable specimen to detect SARS-CoV-2 in mass screening of asymptomatic persons.
