Follow-up testing of borderline SARS-CoV-2 patients by rRT-PCR allows early diagnosis of COVID-19

Abstract

Detection of SARS-CoV-2 RNA in nasopharyngeal samples using the real-time reverse transcription polymerase chain reaction (rRT-PCR) is the gold standard for diagnosing COVID-19. Determination of SARS-CoV-2 RNA by rRT-PCR sometimes results in an inconclusive test result due to a high cycle threshold-value. We retrospectively analyzed 30,851 SARS-CoV-2 rRT-PCR test results. Borderline positivity was considered as the presence of ≤25 viral copies per milliliter, while no amplification was considered as a negative test result. Of all test results, 204 were answered as borderline, of which 107 were accompanied by a follow-up test within 96 hours. Of the 107 follow-up samples, 10 (9.35%) were found positive for SARS-CoV-2. COVID-19 symptoms were not predictive for testing positive in the follow-up test. The positive SARS-CoV-2 samples in the follow-up group represented 0.92% of all positive test results, highlighting the need for retesting and increased hygienic measures for borderline SARS-CoV-2 patients [NCT04636294].

Keywords: Borderline; COVID-19; Molecular diagnostics; SARS-CoV-2; rRT-PCR.

Fig. 1

Description of the patient cohort. (A) Organigram of positive, negative and borderline SARS-CoV-2 rRT-PCR test results. (B) From a total of 204 SARS-CoV-2 borderline samples, 18 were preceded by a positive test result.

Fig. 2

Follow-up of borderline SARS-CoV-2 rRT-PCR results. (A) Ten out of 107 patients (9.35%) tested positive within 96 hours after a borderline SARS-CoV-2 test result. (B) Follow-up viral loads were significantly higher in SARS-CoV-2-positive patients (Wilcoxon signed rank test). (C) Patients with a positive SARS-CoV-2 test result within 96 hours after a borderline test result, did not experience more often COVID-19 symptoms upon first presentation compared to patients that turned out SARS-CoV-2 negative in the follow-up test (Fischer's exact test).