LAUSR

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta variant is considered responsible for worldwide surges in coronavirus disease 2019 (COVID-19) cases in 2021, with increased infectivity compared to the wild type (Wuhan-1). In a previous study, we identified temporal changes in wild-type SARS-CoV-2 RNA load and detection rate in EBC collected from COVID-19 patients. The primary objective of this study was to clarify temporal changes in Delta-variant SARS-CoV-2 RNA load and detection rates in EBC collected from patients, and to validate the feasibility of Delta-variant SARS-CoV-2 RNA detection from EBC for diagnosing COVID-19. The secondary objective was to compare SARS-CoV-2 RNA loads in EBC between Delta-variant and wild-type. Subjects were 41 COVID-19 patients infected with the Delta-variant. EBC samples were collected from subjects on the day of or the day after admission using R-tube® (Respiratory Research, Austin, Texas, USA), as in our previous study. SARS-CoV-2 RNA in EBC samples was detected and quantified by RT-PCR assay targeting the E gene, using the same settings and reagents as in the previous study. The results indicated that SARS-CoV-2 RNA load in EBC collected from subjects infected with Delta-variant decreased exponentially with the passage of days from symptom onset. Sustained high detection rates support the feasibility of Delta-variant SARS-CoV-2 RNA detection from EBC by RT-PCR assay as a diagnostic test for COVID-19 within 8 d of onset. SARS-CoV-2 RNA load in EBC collected 2–8 d from onset was significantly higher in Delta-variant-infected subjects than in wild-type-infected subjects on a day-to-day basis (p = 0.005–0.029). However, because of the heterogeneity of the study cohort, conclusions cannot be reached regarding differences in viral RNA load between strains, regardless of the timing of EBC collection.