Persistent Nonviral Plasmid Vector in Nasal Tissues Causes False-Positive SARS-CoV-2 Diagnostic Nucleic Acid Tests

Area of Science:

• Molecular Biology
• Virology
• Occupational Health

Background:

• Biomedical personnel can be exposed to laboratory reagents.
• Distinguishing between viral infection and reagent contamination is crucial for accurate diagnostics.

Purpose of the Study:

• To investigate the source of persistent positive SARS-CoV-2 PCR results in asymptomatic laboratory workers.
• To determine if positive results were due to community-acquired SARS-CoV-2 or contamination with a laboratory plasmid vector.

Main Methods:

• Longitudinal collection of nasal secretions from asymptomatic laboratory coworkers.
• Real-time PCR testing for SARS-CoV-2 and specific regions of a plasmid vector.
• Differentiating between viral RNA and plasmid DNA amplification.

Main Results:

• Four asymptomatic coworkers had positive SARS-CoV-2 PCR results but negative tests for specific viral proteins.
• Nucleic acids from their nasal swabs amplified regions of a laboratory plasmid vector, including resistance genes.
• Plasmid DNA was detected repeatedly for weeks, even during isolation, suggesting nasal persistence or colonization.

Conclusions:

• Asymptomatic laboratory workers can harbor and shed laboratory plasmid DNA containing SARS-CoV-2 sequences for extended periods.
• Nonviral plasmid vectors can interfere with molecular diagnostic tests.
• Proper personal protective equipment and consideration of occupational exposures are essential to prevent sample contamination and misdiagnosis.