SARS-CoV-2 detection by reverse transcriptase polymerase chain reaction testing: Analysis of false positive results and recommendations for quality control measures.

Testing for SARS-CoV-2 has become a critical component for the management of the COVID-19 pandemic. Reverse transcriptase polymerase chain reaction (RT-PCR) assays are currently the predominate method for testing. Quality control (QC) measures utilize known positive and known negative controls to ensure the adequacy of extraction and RT-PCR steps but do not evaluate all components of testing. We have conducted a quality assurance review of our RT-PCR testing for COVID-19 to determine the rate of false positive results in asymptomatic patients and causes for these errors. DESIGN: We have developed a quality control procedure in which all specimens from asymptomatic unexposed persons with SARS-CoV-2 positive tests were retested. When a second test was "non-detected" a third test was performed and a root cause analysis of the erroneous result undertaken. RESULTS: In the study period, 24,717 samples were tested and 6251 were from asymptomatic patients. Of the 288 initial positive tests, 20 (6.9%) were negative on retesting. Review of cycle threshold curves, technologists' records, location of specimen on testing plates and relationships with high viral load specimens was undertaken. Analysis revealed technologists' errors (misplacement of specimen in testing plate or contamination) and cross contamination from high viral load specimens in adjacent wells of testing plates were common causes for false positive results. DISCUSSION: SARS-CoV-2 RT-PCR testing is associated with a small number of false positive results, most easily recognized in asymptomatic non-exposed patients. Implementation of a limited retesting protocol identifies clinically significant testing errors and allows review and improvement of laboratory procedures.

SARS-CoV-2 show no infectivity at later stages in a prolonged COVID-19 patient despite positivity in RNA testing.

Inpatient coronavirus disease 2019 (COVID-19) cases present enormous costs to patients and health systems in the United States. Many hospitalized patients may continue testing COVID-19 positive even after the resolution of symptoms. Thus, a pressing concern for clinicians is the safety of discharging these asymptomatic patients if they have any remaining infectivity. This case report explores the viral viability in a patient with persistent COVID-19 over the course of a 2-month hospitalization. Positive nasopharyngeal swab samples were collected and isolated in the laboratory and analyzed by quantitative reverse-transcription polymerase chain reactions (qRT-PCR), and serology was tested for neutralizing antibodies throughout the hospitalization period. The patient experienced waning symptoms by hospital day 40 and had no viable virus growth by hospital day 41, suggesting no risk of infectivity, despite positive RT-PCR results which prolonged his hospital stay. Notably, this case showed infectivity for at least 24 days after disease onset, which is longer than the discontinuation of transmission-based precautions recommended by the Center for Disease Control and Prevention. Thus, our findings suggest that the timeline for discontinuing transmission-based precautions may need to be extended for patients with severe and prolonged COVID-19 disease. Additional large-scale studies are needed to draw definitive conclusions on the appropriate clinical management for these patients. ​.