Prolonged SARS-CoV-2 RNA detection by RT-PCR: variability in cycle threshold values over time.

Area of Science:

• Virology
• Molecular Diagnostics
• Infectious Diseases

Background:

• Millions of reverse transcription-polymerase chain reaction (RT-PCR) tests have been performed globally for SARS-CoV-2 detection.
• Various protocols exist, leading to potential variability in results and interpretation.

Purpose of the Study:

• To evaluate the duration of SARS-CoV-2 RNA detectability by RT-PCR at 37°C.
• To analyze changes in cycle threshold (Ct) values over extended incubation periods.
• To inform clinical decision-making regarding repeated RT-PCR testing.

Main Methods:

• 120 positive SARS-CoV-2 nasopharyngeal swabs were stratified into Ct value groups.
• Samples were incubated at 37°C for up to 60 days.
• RT-PCR was repeated at 15-day intervals to assess RNA persistence and Ct value changes.

Main Results:

• Samples with initial Ct <20.0 remained positive throughout the 60-day study.
• Samples with initial Ct >40.0 became negative by day 15.
• A significant proportion of samples with Ct ≤35.0 remained positive at day 60, with decreased positivity correlating with higher initial Ct values.
• Ct values increased over time, but inconsistently by day 60.

Conclusions:

• SARS-CoV-2 RNA can persist for months, leading to prolonged RT-PCR positivity.
• Repeated RT-PCR testing introduces variability in qualitative results and Ct values, complicating clinical decisions.
• Patient monitoring should prioritize clinical assessment and viral viability assays over repeated RT-PCR testing.