SARS-CoV-2 detection by nasal strips: A superior tool for surveillance of paediatric population
Authors: Renee W.Y. Chan, Kate C. Chan, Kathy Y.Y. Chan, Grace C.Y. Lui, Joseph G.S. Tsun, Rity Y.K. Wong, Michelle W.L. Yu, Maggie H.T. Wang, Paul K.S. Chan, Hugh Simon Lam, Albert M. Li
Journal: Journal of Infection (2020)

A reliable, simple and safe sampling method applicable to a wide-age-range is required for community-based SARS-CoV-2 surveillance. Nasopharyngeal/oropharyngeal specimens require trained-personnel to perform and trigger sneezing, and coughing, which pose a risk of disease transmission.1U.S. Food & Drug Administration. Recommendations on Providing Clear Instructions to Patients Who Self-Collect an Anterior Nares (Nasal) Sample in a Health Care Setting for SARS-CoV-2 Testing - Letter to Health Care Providers. In: Administration USFD, ed. 10/07/2020 ed 2020.Google Scholar Self-administered sampling methods2Wyllie AL Fournier J Casanovas-Massana A et al.Saliva or nasopharyngeal swab specimens for detection of SARS-CoV-2.N Engl J Med. 2020; 383: 1283-1286Crossref PubMed Scopus (627) Google Scholar, 3Pere H Podglajen I Wack M et al.Nasal swab sampling for SARS-CoV-2: a convenient alternative in times of nasopharyngeal swab shortage.J Clin Microbiol. 2020; : 58Google Scholar, 4Tu YP Jennings R Hart B et al.Swabs collected by patients or health care workers for SARS-CoV-2 testing.N Engl J Med. 2020; 383: 494-496Crossref PubMed Scopus (175) Google Scholar have been assessed in adult in-patients, but these methods do not translate well to the community setting, e.g., saliva collection is difficult in young children and the elderly, and variably reduces test sensitivity.5Lai CKC Chen Z Lui G et al.Prospective study comparing deep-throat saliva with other respiratory tract specimens in the diagnosis of novel coronavirus disease (COVID-19).J Infect Dis. 2020; Crossref Scopus (30) Google Scholar A recent study published in the Journal of Infection reviewed the methodologies used in the estimation of diagnostic accuracy of SARS-CoV-2 real-time reverse transcription polymerase chain reaction (RT-PCR) and other nucleic acid amplification tests for COVID-19 and pointed out the importance in employing standardized guidelines for study designs and statistical methods.6Axell-House DB Lavingia R Rafferty M Clark E Amirian ES Chiao EY The estimation of diagnostic accuracy of tests for COVID-19: A scoping review.J Infect. 2020; 81: 681-697Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar Here, we compared different sample collection methods and introduced nasal strip as a sensitive and low-risk collection method and assessed its application in both paediatric and adult subjects at the Prince of Wales Hospital, Hong Kong. Thirty-eight asymptomatic and symptomatic subjects hospitalized with COVID-19 were recruited prospectively by convenience sampling. The disease status was confirmed by two RT-PCR tests targeting different regions of the RdRp gene performed by the local hospital and Public Health Laboratory Service. Twenty infected adults (range: 22–74 years old) and eighteen children/adolescents (range: 6–17 years old) were recruited of whom ten were asymptomatic. Adult subjects or guardians of participants below 18 years old provided informed consent (see the Methods section in the Supplmentary Appendix). We obtained nasal epithelial lining fluid (NELF) by nasal strip (n = 43), to compare against pooled nasopharyngeal and throat swabs (NPSTS) (n = 21) or deep throat saliva (DTS) (n = 22) collected within 24 h of the nasal strip. 13 paired nasal swabs were also collected right before the collection of nasal strip to evaluate their SARS-CoV-2 detection performance. All samples were subjected to viral RNA quantitation by real-time PCR targeting the nucleoprotein gene.7Chu DKW Pan Y Cheng SMS et al.Molecular diagnosis of a novel coronavirus (2019-nCoV) causing an outbreak of Pneumonia.Clin Chem. 2020; 66: 549-555Crossref PubMed Scopus (946) Google Scholar Spearman's test demonstrated significant correlation between nasal strip and NPSTS (p = 0.0003) and between nasal strip and DTS (p = 0.01) (Fig. 1A). The agreement between nasal strip samples and NPSTS was 94.44% (17/18) and 100% (3/3) for NPSTS positive and negative samples (Table 1, Fig. 1B). In contrast, the agreement between nasal strip specimens and DTS was 93.33% (14/15) and 14.29% (1/7) for DTS positive and negative samples, respectively (Table 1, Fig. 1C). Eight discrepant samples were identified (Table S1, Figure S1) of which seven were DTS specimens. Nasal strip outperformed DTS on six occasions, where negative result was reported in the latter. Four of these DTS specimens were collected from paediatric patients (Patients 1 to 4). Nasal strip samples were tested negative on two occasions when the reference test revealed Ct values of 35 and 28.92 (Figure S1). Wilcoxon signed rank test revealed that nasal strip and NPSTS gave similar Ct values (Fig. 1D, p = 0.76) while a lower Ct was detected in nasal strip compared to paired DTS (Fig. 1E, p = 0.016).Table 1Number of tested samples and performance of the collection methodsNasal stripReferencePositiveNegativeTotalAgreement (%)NPSTS (n = 21)Positive1711894.44Negative033100.00Value (95% CI)Accuracy95.2 (76.18–99.88)DTS (n = 22)Positive1411593.33Negative61714.29Value (95% CI)Accuracy68.18 (45.13–86.14)No significant difference in the detection rate was observed between NPSTS (McNemar's test p = 1.000) or DTS (p = 0.13) for the qPCR test (NPSTS and DTS, p = 0.29). CT value equal or below 35 is defined as positive. Open table in a new tab No significant difference in the detection rate was observed between NPSTS (McNemar's test p = 1.000) or DTS (p = 0.13) for the qPCR test (NPSTS and DTS, p = 0.29). CT value equal or below 35 is defined as positive. Of the 43 nasal strips collected, 13 were paired with a nasal swab sample obtained concurrently by a healthcare worker. A significant correlation was found between Ct values from the nasal strip and nasal swab specimens (r = 0.88, p = 0.0031, Figure S2A). Though nasal swab missed two positive cases detected by nasal strip and nasal strip missed one positive case detected by nasal swab, there was no significant difference detected between Ct values of the 13 paired samples (Figure S2B). Finally, we collected nasal strip pairs from six patients to determine viral stability over time, viral RNA remained detectable after 24- and 72 h storage at room temperature (Fig. 1F). The high correlation of nasal strip samples with the 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. This study also indicated the possible insensitivity of DTS, particularly in paediatric patients who are less able to provide DTS with consistent quality (Table S1) and how nasal strip would be a superior tool for surveillance of paediatric populations. Nasal strip is also a better collection method than NPSTS as it is less traumatic and irritating. The application of nasal strip reduces the risk of any sneezes and coughs and therefore lessens the risk of virus transmission. Nasal strip is a more comfortable and easier to apply sampling method than the other available standard sampling tools. Repeat nasal strip sampling as part of a community-based surveillance program is feasible in children and adults and likely to succeed as a result of its non-invasive nature (Video 1). Compared with NPSTS, nasal strip sampling achieved an accuracy of 95.2% (Table 1). Nasal strip sample is comparable if not superior to other sampling methods reported in the literature, including self-administered tongue, lower- and mid-nasal specimens.4Tu YP Jennings R Hart B et al.Swabs collected by patients or health care workers for SARS-CoV-2 testing.N Engl J Med. 2020; 383: 494-496Crossref PubMed Scopus (175) Google Scholar Apart from its good accuracy, we assessed the validity of the nasal strip samples after prolonged room temperature storage so as to mimic the duration needed to post the specimens to the laboratory. This aspect was not assessed in previous studies, albeit an important criterion if a sampling method is adopted for community-based testing purposes. Our findings suggest that nasal strip would provide at least consistent qualitative results (positive or negative), as long as the Ct value is within the range of an inferred infectivity.8Perera R Tso E Tsang OTY et al.SARS-CoV-2 virus culture and subgenomic RNA for respiratory specimens from patients with mild coronavirus disease.Emerg Infect Dis. 2020; : 26Google Scholar This would be sufficient to identify potentially infectious individuals and susceptible contacts for further management and quarantine. There are several limitations in this study. This prospective study presents the cross-sectional data performed in a single hospital. The clinical sample pairs (n = 6) that underwent 24- to 72 h room temperature storage remained stable in terms of viral detection. However, the involvement of protease and RNase activity of individual subjects and its contribution to sample stability has not been fully elucidated. The current method provides detection of SARS-CoV-2 at the gene level but no information was obtained regarding the infectious titer. Our nasal strip collection method serves as an excellent sampling method with comparable performance with NPSTS, DTS and nasal swab specimens in identifying subjects infected with SARS-CoV-2. This reliable, non-invasive, self-administered method with its extended sample stability makes it uniquely suited for repeated sampling and large-scale community study, especially for paediatric population.