A polymerase chain reaction (PCR) test via a single nasopharyngeal swab to diagnose severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has both value and limitations, according to a study recently published in Open Forum Infectious Diseases.
At the beginning of this pandemic, testing for SARS-CoV-2 was selectively administered to identify and isolate those who were infected. However, there was a lack of objective evidence to determine pre-test probability and predictive value of these tests. This retrospective, cross sectional, observational study analyzed SARS-CoV-2 healthcare worker testing at a tertiary care hospital in Long Island, New York.
In total, 105 healthcare workers with COVID-19-like symptoms or significant COVID-19 exposure who underwent both SARS-CoV-2 PCR testing and antibody testing from March 1, 2020 to April 30, 2020 were included. Significant exposure was defined as at least 15 minutes in close proximity to a patient with SARS-CoV-2 without wearing personal protective equipment.
The reverse transcription (RT)-PCR test was performed on a nasopharyngeal specimen. All included workers completed a questionnaire to self-report symptoms experienced before the initial PCR test. Additionally, all workers underwent testing for the presence of SARS-CoV-2 Immunoglobulin G (IgG) antibodies at least 3 weeks after the onset of their symptoms. The date and result of SARS-CoV-2 PCR, the date and result of antibody testing, and symptoms on presentation were analyzed. Symptoms were aggregated and compared with SARS-CoV-2 PCR and antibody tests and via a 2-tailed z-test.
Results demonstrated both the value and limitations of a single PCR nasopharyngeal swab to diagnose SARS-CoV-2 infection. Of the 105 included healthcare workers, 58.1% of workers tested positive via the SARS-CoV-2 PCR test and 41.9% of workers tested negative. Of the 61 healthcare workers that tested positive, 98.4% of workers had antibodies while 1.6% had no antibodies.
Of the 44 healthcare workers who were negative, 20.5% of the workers had antibodies. The SARS-CoV-2 PCR test via a single nasopharyngeal swab had 87% sensitivity, 97% specificity, a positive predictive value of 0.98, and a negative predictive value of 0.80 for symptomatic patients. In total, 76 healthcare workers reported symptoms at the time of administration of the SARS-CoV-2 PCR test, with the most common symptom being cough.
Statistical analysis of a larger group of employees (n=461; including these 105 employees) showed that the symptoms of cough and myalgia were significantly different between those with and without antibodies (P =.0108 and P =.0009, respectively).
Limitations of this study included self-reported symptoms that lacked objective verification, and the calculated specificity was dependent on the assumption that employees did not become infected between the screening test and the antibody test.
“Determining likelihood of COVID illness using diagnostic PCR testing has not been fully determined,” the researchers concluded. “The lack of availability of adequate SARS-CoV-2 testing, reports of high false negative tests, and variability of symptoms on presentation hinder accurate diagnosing.”
“The high [positive predictive value] seen in this study reinforces the rationale for PCR testing to identify new cases,” they added.
George B, McGee J, Giangrasso E, et al. What is the predictive value of a single nasopharyngeal SARS-CoV-2 PCR swab test in a patient with COVID-like symptoms and/or significant COVID-19 exposure? [published online September 1, 2020] Open Forum Infect Dis. doi: 10.1093/ofid/ofaa399/5899824