421 - If at first you do not succeed…. Repeat SARS-COV2 PCR testing

Background: Nucleic Acid Amplification Tests (NAATs) of nasopharyngeal specimens (NPS) have become standard for diagnosis of SARS-COV2. IDSA guidelines suggest repeat testing after 24-48 h when initially negative and clinical suspicion persists.  We characterized patients from whom initial NPS were NAAT-negative, but repeats were NAAT-positive, in order to identify which patients might benefit from repeat NAAT for SARS-CoV-2, and the appropriate interval. 

Methods: We conducted an IRB-approved retrospective review of laboratory and electronic medical record data for all patients evaluated for SARS-CoV-2 infection at the Mount Sinai Health System, whose initial NAATs were done between March 16 – March 30, 2020, and who were retested within one month.  NAATs were performed on NPS in viral transport medium using the Roche Diagnostics cobas® 6800 SARS-CoV-2 Test.  Baseline patient characteristics, clinical and radiographic findings were identified.

Results: Of 235 patients eligible for inclusion, 172 (70.5%) were initially NAAT-negative, and 118 (68.6%) remained NAAT-negative over 1 month follow up.  54 (31.4%) converted to NAAT-positive over the next 1-month. Of patients who became NAAT-positive, 31 (57.4%) were inpatients who converted results within a single admission; the average interval was 6d 7h between the NAAT-negative and NAAT-positive results, and the minimum interval was 10.5 h.   Symptoms examined for correlation for conversion to NAAT-positive were: fever, cough, shortness of breath, and combined nausea/vomiting/diarrhea. Duration of symptoms reported at triage did not appear to affect time to conversion to NAAT-positive. No individual symptom was more likely to be associated with conversion to NAAT- positive. However, time to conversion to NAAT-positive was shorter for patients with multiple symptoms. In general, chest radiography (CXR) findings correlated with NAAT results; interval to NAAT-positive was shorter for patients with worsening CXR findings.

Conclusion: Our data supports repeat testing in patients with multiple clinical symptoms suggestive of SARS CoV-2 infection and negative initial NP test results.  Further studies are needed to determine the true clinical sensitivity and specificity of SARS-CoV-2 NAAT assays.