Why has the NHS done away with nasopharyngeal swabs?
Dear Editor,
Helen Salisbury raises concerns that patients are advised through the government website that a negative test means they do not have coronavirus. As she says, this advice is clearly not true as false-negative rates are high – Salisbury quotes a figure of roughly 30% for self-testing.
Salisbury goes on to say that, “it’s not clear how much this is due to the inconsistent presence of the virus in the nasopharynx and how much to the difficulty of correctly taking the swabs”. However, many of these patients are not getting nasopharyngeal swabs. Nasal swabs have largely replaced nasopharyngeal swabs in the NHS (see advice from PHE [1],[2]). This appears to have happened without much discussion or awareness among healthcare professionals and patients. These are very different tests. The nomenclature is confusing as ‘nasal tests’ relate to swabbing the inside of the nose and the same expression is often used (incorrectly) for for nasopharyngeal swabs taken through the nose, of the upper pharynx.
Much of our limited knowledge on testing for SARs-CoV-2 virus comes from literature related to oropharyngeal swabs and nasopharyngeal swabs.[3] Many other countries continue to use nasopharyngeal tests, (with or without oropharyngeal), and taking both is still advised by the World Health Organisation.[4] The accuracy of the tests is compromised by self-testing and will be even further compromised by replacing a nasopharyngeal swab with a nasal swab, based on even more limited evidence.[5] For many people nasal swabs are easier, and more acceptable and self-testing reduces the demand for Personal Protective Equipment (PPE). They may allow a greater volume of testing, which the government is keen to achieve, but this compromise, and the reasoning behind it should be explicit. Telling patients they have not got COVID based on a single negative test done using this compromise is even more misleading. False-negative tests have major public health ramifications, alongside clinical implications for the individual.
Rapid Response:
Why has the NHS done away with nasopharyngeal swabs?
Dear Editor,
Helen Salisbury raises concerns that patients are advised through the government website that a negative test means they do not have coronavirus. As she says, this advice is clearly not true as false-negative rates are high – Salisbury quotes a figure of roughly 30% for self-testing.
Salisbury goes on to say that, “it’s not clear how much this is due to the inconsistent presence of the virus in the nasopharynx and how much to the difficulty of correctly taking the swabs”. However, many of these patients are not getting nasopharyngeal swabs. Nasal swabs have largely replaced nasopharyngeal swabs in the NHS (see advice from PHE [1],[2]). This appears to have happened without much discussion or awareness among healthcare professionals and patients. These are very different tests. The nomenclature is confusing as ‘nasal tests’ relate to swabbing the inside of the nose and the same expression is often used (incorrectly) for for nasopharyngeal swabs taken through the nose, of the upper pharynx.
Much of our limited knowledge on testing for SARs-CoV-2 virus comes from literature related to oropharyngeal swabs and nasopharyngeal swabs.[3] Many other countries continue to use nasopharyngeal tests, (with or without oropharyngeal), and taking both is still advised by the World Health Organisation.[4] The accuracy of the tests is compromised by self-testing and will be even further compromised by replacing a nasopharyngeal swab with a nasal swab, based on even more limited evidence.[5] For many people nasal swabs are easier, and more acceptable and self-testing reduces the demand for Personal Protective Equipment (PPE). They may allow a greater volume of testing, which the government is keen to achieve, but this compromise, and the reasoning behind it should be explicit. Telling patients they have not got COVID based on a single negative test done using this compromise is even more misleading. False-negative tests have major public health ramifications, alongside clinical implications for the individual.
[1] https://assets.publishing.service.gov.uk/government/uploads/system/uploa... [Accessed 5 June 2020]
[2] https://www.gov.uk/government/publications/covid-19-guidance-for-taking-... [Accessed 5 June 2020]
[3] https://www.cebm.net/covid-19/comparative-accuracy-of-oropharyngeal-and-... [Accessed 5 June 2020]
[4] https://apps.who.int/iris/bitstream/handle/10665/331329/WHO-COVID-19-lab... [Accessed 5 June 2020]
[5] https://www.nejm.org/doi/full/10.1056/NEJMc2016321?query=TOC [Accessed 5 June 2020]
Competing interests: No competing interests