Estimating the false-negative test probability of SARS-CoV-2 by RT-PCR

Area of Science:

• Infectious Diseases
• Diagnostic Testing
• Epidemiology

Background:

• Reverse-transcription PCR (RT-PCR) is a key diagnostic tool for SARS-CoV-2 infection.
• While RT-PCR offers high specificity, false negatives can occur, influenced by sample type and time post-symptom onset.

Purpose of the Study:

• To investigate the impact of time since symptom onset and swab type on false-negative rates in SARS-CoV-2 RT-PCR testing.
• To assess the effect of repeat testing on diagnostic accuracy.

Main Methods:

• Analysis of publicly available data from patients with multiple RT-PCR tests for SARS-CoV-2.
• Utilized generalized additive mixed models to analyze test results in relation to time since symptom onset and sample type.

Main Results:

• The likelihood of a positive SARS-CoV-2 test decreases as time passes after symptom onset.
• Nasopharyngeal (NP) swabs demonstrated higher sensitivity compared to oropharyngeal (OP) swabs.
• Repeating negative tests 24 hours later significantly reduced the probability of false-negative results.

Conclusions:

• Nasopharyngeal swabs are more sensitive for detecting SARS-CoV-2 than oropharyngeal swabs.
• Delayed RT-PCR testing after symptom onset increases the risk of false negatives, impacting patient identification and contact tracing.
• Repeat testing protocols can improve diagnostic reliability and inform decisions regarding patient isolation and discharge.