Comparison of Nasal and Nasopharyngeal Swabs for ...

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Study Overview

Objective

This study aims at determining the disparities in influenza detection using nasal and nasopharyngeal swabs with various test types.

Design

We conducted a prospective study.

Setting

Participants were enrolled in central Wisconsin from January to March 2007.

Participants

Adult patients with acute respiratory illnesses less than 10 days were evaluated and included in the study.

Methods

Paired nasal and nasopharyngeal swabs were taken from consenting adults, tested using real-time reverse transcriptase polymerase chain reaction (rRT-PCR) and viral culture. A composite measure of positivity acted as the golden standard, whereby any positive result by either test from either specimen was deemed a positive case.

Results

Out of 240 participants, 33 (14%) tested positive for influenza using rRT-PCR. Sensitivity for nasal swabs was 89%, while for nasopharyngeal swabs it was 94%, with no significant sensitivity differences noted between swab types.

Conclusion

When using highly sensitive molecular diagnostics, sensitivity did not significantly differ between swab types, although the study was underpowered to identify small differences.

Keywords:

Detection, Influenza virus, Specimen type

Introduction

Influenza is a major global health issue, causing numerous deaths annually in the United States. Accurate, timely, and patient-friendly testing is imperative due to pandemic threats and antiviral resistance.

Specimens for flu testing include nasopharyngeal (NP) swabs, oropharyngeal swabs, nasal washes, and nasal aspirates. NP wash is often ideal for virus isolation but it is inconvenient and uncomfortable for most patients.

Swabs provide a more convenient, quicker option but require more sensitivity comparison data. Most studies focus on children or older diagnostic techniques, with limited data on nasal and NP swabs in adults.

Various influenza diagnostic techniques exist, with viral culture considered the gold standard. Yet, it takes up to 7 days for results, which limits its practical use. Recent techniques like rRT-PCR offer potential improvements in diagnostic sensitivity.

Our prospective study analyzed the difference in influenza detection using paired nasal and NP swabs tested by both viral culture and rRT-PCR. While consent was taken from every participant, all procedures were validated by the Institutional Review Board of Marshfield Clinic.

Research Methods

Participants

Adults with acute respiratory illness (less than 10 days) were included in the study between January and March of 2007.

Clinical Specimens

Both nasal and NP swabs were collected. NP swabs were collected using an aluminum/plastic unishaft swab, while nasal swabs were collected using a large-tipped plastic shafted Dacron swab.

All collected samples were stored in viral transport media and refrigerated for less than 24 hours before freezing for testing.

Diagnostic Techniques

Both rRT-PCR and viral cultures were performed at the same facility. Using specific protocols, the samples underwent rigorous testing, ensuring reliability of the results.

Statistical Analysis

Sensitivities and 95% confidence intervals were calculated. All data were analyzed using SAS 9.2 with significant P values being <0.05.

Study Results

Nasal and NP swabs were collected from 240 patients. Patient demographics showed a median age of 60 years, mostly female participants, and a subset having had flu vaccinations and chronic conditions.

Influenza positivity was confirmed in 35 cases. Sensitivities of swab types differed, with nasal swabs showing lower sensitivity in viral cultures but high sensitivity in rRT-PCR tests.

Discussion

Our findings indicate that nasal swabs are slightly less sensitive than NP swabs, but the differences were not statistically significant.

In conclusion, nasal swabs offer a less invasive yet comparable alternative for influenza detection, especially when using molecular diagnostic methods like rRT-PCR.

Conclusion

Although traditional methods rely on viral culture, less invasive approaches like nasal swabs have shown potential for effectiveness in detecting influenza through modern molecular techniques.

Acknowledgments

We thank all participants and staff involved in the study for their contributions.

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Financial Disclosure: Funding for this research was provided by a cooperative agreement with the Centers for Disease Control and Prevention, Atlanta, GA (1 U01 CI000192-01).

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