SMH – St. Michael’s Hospital Medical Services Association
SMH-21-006 – Detection of COVID-19 virus from infection control surveillance specimens
To our knowledge, this is the first study to assess the utility of combined nasal and rectal (N/R swab) specimens for the detection of SARS-CoV-2. We focused our analysis on participants with laboratory confirmed COVID-19 and detected SARS-CoV-2 in 39% of their N/R screening swabs.
Our data highlight several important findings. First, as a proof of concept in our stability studies, N/R swabs can be used to detect SARS-CoV-2 as is evidenced by our findings that the virus is stable after 7 days of storage at 4°C. Secondly, N/R swabs performed poorly with a low detection rate and lower Ct-value compared to paired NPS. Lastly, our retrospective chart review analysis did not demonstrate an association between a participant’s clinical syndrome or severity of disease and the detection of SARS-CoV-2 in their N/R swab, suggesting that a targeted approach for surveillance to a particular cohort may not be fruitful.
A major limitation of this study is the inability to evaluate if SARS-CoV-2 was shed from nasal or rectal collections, however, studies reported high detection rates (> 80%) of SARS-CoV-2 from nasal swabs and rectal swabs. In contrast, the detection rate of SARS-CoV-2 from faecal specimens is lower (25-67%). The discrepancy between detection rates might be due to disparities in sampling time relative to symptom onset, specimen collection guidelines, and/or various chemistries used in nucleic acid extraction and RT-PCR. Of note, we diluted our N/R swabs 10-fold prior to nucleic acid extraction which may contribute to the lower detection rate observed in this study.
Despite the limitations and lack of sensitivity, N/R swabs may still pose to be diagnostically useful in certain circumstances (such as if NPS supply is very low) but should not be used as the sole specimen type for the diagnosis of SARS-CoV-2 infection. Theme
Methods of Risk Reduction and Mitigation
Primary Project Lead for Contact
Dr. Linda Taggart
Secondary Project Lead for Contact
Dr. Matthew Muller