PCR Testing May Not Be Sensitive for COVID-19 in Early Stages of Disease Course

Nasopharyngeal swab tests may not be sensitive for coronavirus disease 2019 (COVID-19) at early stages of the clinical presentation, according to a brief report published in Clinical Infectious Diseases.

The report highlighted 3 patients with COVID-19 pneumonia with initial negative swab test results before computed tomographic (CT) examination and eventual confirmation of infection with severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2) by real-time reverse-transcription polymerase chain reaction (RT-PCR) assay.

All 3 patients had a definitive history of exposure to close contact with an individual with confirmed COVID-19. Despite a negative RT-PCR on swab sample, chest CT findings were positive with a pattern consistent with COVID-19 pneumonia. In patient 1, the disease was in the progressive stage, with bilateral features, multifocal fusion structure of ground glass opacity, and multilobular infiltration. CT imaging of patients 2 and 3 showed mild pneumonia, with peripheral multifocal ground-glass opacities and interlobular septal thickening.

Of note, detection of viral nucleic acid was still negative in the 3 patients on day 6 to 8 after onset of disease.

These cases suggest that PCR testing of nasopharyngeal swabs is likely not sensitive for COVID-19 at early stages of the clinical presentation and that chest CT may help in screening suspected cases and may predict severe complications such as acute respiratory diseases.

Reference

Xu J, Wu R, Huang H, et al. Computed tomographic imaging of 3 patients with coronavirus disease 2019 pneumonia with negative virus real-time reverse-transcription polymerase chain reaction test [published online March 31, 2020]. Clin Infect Dis. doi:10.1093/cid/ciaa207