Abstract
We performed a prospective study of 501 patients, regardless of symptoms, admitted to the hospital, to estimate the predictive value of a negative nasopharyngeal swab for severe acute respiratory coronavirus virus 2 (SARS-CoV-2). At a positivity rate of 10.2%, the estimated negative predictive value (NPV) was 97.2% and the NPV rose as prevalence decreased during the study.
Highlights
Of the 463 negative index nasopharyngeal swab (NP swab), 13 had a corresponding positive result on the second NP swab, yielding an index swab NPV of [1 − (13/463)] or 97.2% (Table 1)
For period 2, not available for period 3, and 99.2% for period 4. These findings indicate an upward trend in NPV, as would be expected by the decreasing prevalence of COVID-19 across the study period
The calculated positivity rate for the three 11-day intervals during which 2 swabs could be performed in this study, correlates significantly with the actual positive test rate for our health system (R2 > 0.99; P < .01)
Summary
The primary objective of this study was to estimate the NPV for an NP swab
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