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Open Access Research article

Flocked nasal swab versus nasopharyngeal aspirate for detection of respiratory tract viruses in immunocompromised adults: a matched comparative study

Lars Öhrmalm*, Michelle Wong, Maria Rotzén-Östlund, Oscar Norbeck, Kristina Broliden and Thomas Tolfvenstam

BMC Infectious Diseases 2010, 10:340  doi:10.1186/1471-2334-10-340

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Response to Dr. Marek Smieja,

Lars ��hrmalm   (2012-12-10 10:18)  Karolinska Institutet

Dr. Marek Smieja,

Thank you for your valuable comments!

I agree that the depth is an important variable �� maybe the most important? However, we wanted to evaluate the possibility of using a depth of 1-1.5 cm in order to minimize the risk of discomfort. Although far from the probable site of replication, the sensitivity of real-time PCR could have compensated for that. We found NPA significantly superior to the fNS in collecting epithelial cells and discussed that this could be the reason for the difference (although not statistically significant) in viral detection between the methods. Once again, thank you for your comments and recommendations!

Kind regards,
Lars ��hrmalm, MD PhD
Karolinska Institutet/Karolinska University Hospital

Competing interests

The authors declare that they have no competing interests.

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Not all Nasal Swabs Are Equivalent: Nasal Anterior Nares Swabs and Nasal Mid-Turbinate Swabs

Marek Smieja   (2011-03-03 16:34)  McMaster University email

I congratulate Dr. Ohrmalm and colleagues for this study comparing nasal swabs with nasopharyngeal aspirates. I share their enthusiasm for examining pre-analytic aspects of specimen collection to optimize diagnostic yield while maintaining patient comfort and staff biosafety.

As an infectious diseases physician, microbiologist and researcher who has invested considerable time and effort in examining nasal-based diagnostics, I would like to point out potential limitations to the current study:

1. The anatomical site of investigation for the “nasal swab” was the anterior nares, 1.0-1.5 cm into the nose, using a swab designed for sampling this site for methicillin-resistant Staphylococcus aureus (MRSA). We have designed a nasal “mid-turbinate” swab which is inserted 4-5 cm and samples the epithelial lining of the mid-turbinate bones (Copan Italia # 56380CS01 {adult} or # 56750CS01 {child}) , and have published data to support excellent sampling of respiratory epithelial cells and high diagnostic yield (Journal of Clinical Microbiology 2010, Smieja et al). I would recommend that researchers carefully distinguish between anterior nares and mid-turbinate sites of sampling, to avoid confusion.

2. The authors refer to the NPA being “significantly” better than the nasal swab. However, I calculate a P-value for the comparison of 0.18 (McNemar test, SPSS), which is not significant. I agree with the impression that the anterior nares swab is likely inferior, and was pleased to see that the authors used beta-actin measurements supporting worse sampling efficacy. In contradistinction, the flocked nasal mid-turbinate swab has sampling values for beta-actin comparable to flocked nasopharyngeal swabs (log 4.82 versus log 4.83). I suggest that the authors consider studying the nasal mid-turbinate swabs in future. A key question is whether diagnostics is simply an issue of high cell yield (approximated by beta-actin quantitation), or whether the nasopharyngeal site truly is more sensitive for diagnosis of respiratory viruses.

3. In addition to the higher level of training required to perform NPA, there is also a higher risk of biohazard to the medical staff taking the specimen. Nasopharyngeal and nasal mid-turbinate swabs offer similar diagnostic yield with potentially lower biohazard. Self-collected nasal mid-turbinate swabs offer the lowest risk of biohazard, and we have successfully collected over 5,000 of these swabs in various studies using self- or parental-sampling.

Sincerely, Marek Smieja, MD PhD

McMaster University
Hamilton, Ontario, Canada.
smiejam@mcmaster.ca

Competing interests

I collaborated with Copan to develop the nasal mid-turbinate flocked swabs, with grant support from the Canadian Institutes of Health Research (CIHR), the major funder of peer-reviewed reseach in Canada.

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