Less Invasive SARS-CoV-2 Tests Comparable and Effective in Nursing Homes

NEW YORK (Reuters Health) – Saliva specimens (SA), anterior nasal swab (AN) and oropharyngeal swab (OP) are all effective methods for SARS-CoV-2 testing in nursing home residents, say researchers with the U.S. Centers for Disease Control and Prevention (CDC).

Nursing homes often need to screen residents for SARS-CoV-2 repeatedly and may opt for gentler and easier ways to obtain specimens than the gold-standard nasopharyngeal swab (NP).

With the broader use of alternative specimen types, CDC researchers saw a need for a direct comparison of SA, AN and OP results to determine the interchangeability of these specimen types for SARS-CoV-2 detection.

Paige Gable, with the CDC COVID-19 Response Team, and colleagues studied a convenience sample of 17 nursing home residents who were within 15 days of a first positive SARS-CoV-2 test by real-time reverse transcription polymerase chain reaction (RT-PCR) and who were prospectively followed for 42 days.

AN, OP and SA were collected on day 1 and every three days for the first 21 days, then weekly for 21 days. The specimens were tested for presence of SARS-CoV-2 RNA using RT-PCR and replication-competent virus by viral culture.

“Comparing the three specimen types collected from each participant at each time point, the concordance of paired RT-PCR results ranged from 80% to 88%,” the researchers report in Clinical Infectious Diseases.

After the first positive result, SA and OP were RT-PCR-positive for 48 days or less; AN swab tests were RT-PCR-positive for 33 days or less.

AN had the highest percentage of RT-PCR-positive results (81%) when collected at or before 10 days of participants’ first positive result.

Eleven specimens were positive by viral culture: nine AN collected at or before 19 days following the first positive result and two OP collected at or before five days following first positive result.

In this study comparing SARS-CoV-2 RT-PCR results across specimen types, AN, OP, and SA “usually produced concordant results” and are effective methods for repeated testing in nursing home residents, Gable and colleagues write.

They note that obtaining AN swab samples is “convenient, non-invasive, and adequate for the detection of SARS-CoV-2 by RT-PCR” and, in this assessment, “yielded more information on the presence of infectious virus while also having a shorter post-shedding duration of RT-PCR positivity.”

“Together, these indicators demonstrate that AN have the potential to minimize the inadvertent detection of previously resolved infections while still capturing those most likely capable of transmitting virus,” they add.

“In nursing home settings, AN may provide more accurate results than other specimen types during acute SARS-CoV-2 infection and allow facilities to better allocate public health resources appropriately. The utility of AN is particularly notable given the current recommendations and focus on rapid point-of-care antigen tests, which also require nasal specimens, albeit the composition of the swab and use of transport medium varies,” they conclude.

The study did not have commercial funding.

SOURCE: https://bit.ly/3yUmyrH Clinical Infectious Diseases, online May 25, 2021.

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