Nasal strips comparable to standard sampling methods for SARS-CoV-2 detection

Collection of nasal epithelial lining fluid (NELF) using nasal strips enables simple, sensitive and low-risk detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with comparable accuracy vs standard sampling methods, highlighting its potential role in large-scale surveillance of coronavirus disease 2019 (COVID-19) across different age groups in the community.

The new sampling method, introduced by researchers from the Department of Paediatrics, Chinese University of Hong Kong (CUHK), has been evaluated against pooled nasopharyngeal swabs and throat swabs (NPSTS) as well as deep throat saliva (DTS) samples in 38 patients (20 adults aged 22–74 years and 18 children or adolescents aged 6–17 years; asymptomatic, n=10) hospitalized with COVID-19. [J Infect 2020, doi: 10.1016/j.jinf.2020.11.009]

A total of 43 nasal strip samples were compared with 21 NPSTS samples and 22 DTS samples collected within 24 hours after nasal strip sampling. Thirteen paired nasal swabs were also collected immediately before nasal strip sampling to evaluate SARS-CoV-2 detection performance.

“Results showed significant correlation between nasal strip and NPSTS samples [p=0.0003], and between nasal strip and DTS samples [p=0.01],” said Dr Renee Chan, first author of the study. “The agreement between nasal strip and NPSTS samples was 94.44 percent and 100 percent for NPSTS-positive and NPSTS-negative samples, respectively. The accuracy of nasal strips was 95.2 percent compared with NPSTS.”

The agreement between nasal strip and DTS samples was lower, at 93.33 percent and 14.29 percent for DTS-positive and DTS-negative samples, respectively, resulting in 68.2 percent accuracy of nasal strips compared with DTS.

“Seven of the eight discrepant samples involved DTS specimens. Nasal strips outperformed DTS on six occasions, where DTS showed negative results while nasal strips revealed positive results,” said Chan. “Of note, four of these DTS specimens were collected from paediatric patients, highlighting possible insensitivity of DTS in paediatric patients who are less able to provide DTS with consistent quality.”

Furthermore, nasal strips demonstrated no significant difference in cycle threshold (Ct) values compared with nasal swab samples obtained concurrently. A significant correlation was found between Ct values of the nasal strip and nasal swab specimens (r=0.88; p=0.0031).

“A lower Ct value was detected in nasal strip vs paired DTS samples [p=0.016],” said Chan.

“We also evaluated the validity of nasal strip samples after prolonged storage in room temperature, to mimic the duration needed to post the specimens to the laboratory,” she continued. “Results from nasal strip pairs from six patients showed that viral RNA remained detectable after 24 hours and 72 hours of storage in room temperature.”

According to the researchers, the high correlation between nasal strip and standard sampling methods is likely the result of steady NELF absorption with the strip in close contact with the nasal mucosa, which reduces sample variability.

“Compared with NPSTS, nasal strip sampling is less traumatic, less irritating, reduces the risk of sneezing and coughing, and hence, the risk of virus transmission during sample collection,” explained Chan. “Sampling with nasal strips can be completed in 1 minute, and can be self-administered in children 6 years of age or above.”

“Our results indicate that nasal strip sampling is superior to DTS for community-based surveillance of COVID-19, particularly in paediatric and elderly populations in whom the sensitivity of DTS testing is shown to be reduced,” she concluded.