Smell Dysfunction

Since the onset of the COVID-19 pandemic there have been an increasing number of patients suffering from smell disorders. This can have a significant impact on patients' quality of life.

Basic silhouette in a circle, in light grey

Mr Umar Rehman, BMBS, MSc, BSc, PGCME, MRCS (Eng)

PhD Candidate and Clinical Research Fellow

Background

Since the onset of the COVID-19 pandemic, our research team have worked hard to contribute to our knowledge of smell disorders. We have published the first case series on healthcare workers in the UK and demonstrated a high incidence of self-reported anosmia amongst healthcare workers across different healthcare systems in the UK, which highlighted the need to address the long-term effects of these symptoms. Crucially, this work identified that females, particularly those above forty years of age, and those with concurrent distorted perception of smell (parosmia), were more likely to experience persistent smell loss. Based on the above, we have run one of the largest prospective multi-institutional clinical studies on Covid-19 associated anosmia in the UK, investigating the course of symptoms over one-year (COVANOS UK study).

A woman smelling a bouquet of flowers in a park or garden setting

More recently, we have conducted two prevalence surveys in a representative sample (gender-matched and age-matched) of the US (n=4,369) and the UK (n=1,160) population. In the US survey, the rates of persistent anosmia (beyond 6 months) and parosmia were reported as 2.7% and 0.9%, respectively, which extrapolates to 9.0 million (95% CI: 7.6 million to 10.8 million) and 3.1 million (95% CI: 2.3 million to 4.2 million) affected individuals in the US, alone. In the UK, the observed rates of persistent anosmia (beyond 12 months) and parosmia were 1.0% and 0.9%, respectively, which is equivalent to 695,331 (95% CI: 398,416 – 1.2 million) and 637,386 (95% CI: 356,454 – 1.1 million) affected individuals, demonstrating the immense burden of long-term smell dysfunction due to COVID-19 (studies completed and manuscript submitted). The similarity in the rates observed between the two countries demonstrates the robustness of these findings and is in line with other studies which altogether demonstrate the significant burden of Covid-19-associated smell loss.

This study demonstrated that 70% of those who experience smell problems due to Covid-19 infection spontaneously recover within the first month. However, the remaining 30% of participants continue to experience some degree of olfactory loss even after this time-point. Importantly, 60% of our participants who had objective smell loss at enrolment saw no improvement in their sense of smell at the one-year follow-up, implying that spontaneous recovery is more unlikely to occur if olfactory dysfunction persists beyond one month at the outset.

Ultimately, we confirm that, even though many will spontaneously recover their sense of smell shortly after onset, there is a significant proportion of individuals who will suffer long-term olfactory dysfunction, as seen at our one-year follow-up, with a high prevalence of continued objective olfactory loss and symptoms of a distorted sense of smell. More recently, we have conducted two prevalence surveys in a representative sample (gender-matched and age-matched) of the US (n=4,369) and the UK (n=1,160) population.

In the US survey, the rates of persistent anosmia (beyond 6 months) and parosmia were reported as 2.7% and 0.9%, respectively, which extrapolates to 9.0 million (95% CI: 7.6 million to 10.8 million) and 3.1 million (95% CI: 2.3 million to 4.2 million) affected individuals in the US, alone. In the UK, the observed rates of persistent anosmia (beyond 12 months) and parosmia were 1.0% and 0.9%, respectively, which is equivalent to 695,331 (95% CI: 398,416 – 1.2 million) and 637,386 (95% CI: 356,454 – 1.1 million) affected individuals, demonstrating the immense burden of long-term smell dysfunction due to COVID-19 (studies completed and manuscript submitted). The similarity in the rates observed between the two countries demonstrates the robustness of these findings and is in line with other studies which altogether demonstrate the significant burden of Covid-19-associated smell loss.

We have now received funding from the Rosetrees Trust to run two more major trials on COVID-19-associated smell loss/anosmia and distorted sense of smell/parosmia and an associated translation programme (COVANOS-2 and COPANOS trials including a translational programme).

We are closely working with the charity Fifth Sense. Mr Lechner serves as Research Hub Co-Lead for Clinical Trials and Epidemiology and has facilitated the development of a questionnaire to evaluate Smell and Taste Dysfunction (SmellQx)

Mr Lechner serves as a Co-I of the I-smell project. The I-smell Project has received funding from the Engineering and Physical Sciences Research Council (EPSRC) as part of UKRI and the National Institute of Health Research (NIHR). EPSRC Reference: EP/W031574/1.

We are collaborating with Prof. Eleni Nastouli on the ‘SARS-CoV-2 Acquisition in Frontline Healthcare Workers - Evaluation to inform Response – PLUS‘ Study (SAFER PLUS Study) with a specific focus on smell dysfunction.

We are collaborating with Professor Hugh Montgomery in investigating smell disorders within the Intensive Care Unit setting.

The UK Smell and Taste Disorders MDT and Education Programme provides a platform for shared learning, discussion of patients with smell and taste disorders (SATDs), and continuous professional development.

Physicians, surgeons, general practitioners and other health and social care professionals are welcome to attend. The meetings will be held virtually on a monthly basis, with an annual face-to-face session as part of the University of East Anglia and Fifth Sense Smell and Taste Symposium in Norwich.

These will be focused on the diagnosis, treatment and management of patients with smell and taste disorders. The sessions will include talks from guest clinicians with experience of treating patients with SATDs, discussions around evaluation and management options and examples of complex cases. Please note that these sessions are for healthcare professionals only and an NHS email address will be needed to register for the meetings.

Our education sessions are aimed at both public and professionals and focus on specific topics, including the different causes of smell and taste disorders. They will include talks from patient representatives and clinicians on specific issues.

Key publications

  1. Lechner M, Liu J, Counsell N, Yan CH, et al. High prevalence of persistent smell loss and qualitative smell dysfunction during the coronavirus disease 2019 (COVID-19) pandemic in the United States: Urgent need for clinical trials. Int Forum Allergy Rhinol. 2023 Aug;13(8): 1558-1560.
  2. Lechner M, Liu J, Counsell N, Gillespie D, et al. The burden of olfactory dysfunction during the COVID-19 pandemic in the United Kingdom. Rhinology. 2023 Feb 1;61(1): 93-96.
  3. Lechner M, Liu J, Counsell N, Gillespie D, et al. The COVANOS trial - insight into post-COVID olfactory dysfunction and the role of smell training. Rhinology. 2022 Jun 1;60(3): 188-199.
  4. Patel ZM, Holbrook EH, Turner JH ... Lechner M, et al. International consensus statement on allergy and rhinology: Olfaction. Int Forum Allergy Rhinol. 2022 Apr;12(4): 327-680. Erratum in: Int Forum Allergy Rhinol. 2023 Sep;13(9): 1844.
  5. Shahrvini B, Prajapati DP, Said M ... Lechner M, Yan CH. Risk factors and characteristics associated with persistent smell loss in coronavirus disease 2019 (COVID-19) patients. Int Forum Allergy Rhinol. 2021 Aug;11(8): 1280-1282.
  6. Makaronidis J, Firman C, Magee CG, Mok J, Balogun N, Lechner M, et al. Distorted chemosensory perception and female sex associate with persistent smell and/or taste loss in people with SARS-CoV-2 antibodies: a community based cohort study investigating clinical course and resolution of acute smell and/or taste loss in people with and without SARS-CoV-2 antibodies in London, UK. BMC Infect Dis. 2021 Feb 25;21(1): 221.
  7. Lechner M, Liu J, Counsell N, Ta NH, et al. Course of symptoms for loss of sense of smell and taste over time in one thousand forty-one healthcare workers during the Covid-19 pandemic: Our experience. Clin Otolaryngol. 2021 Mar;46(2): 451-457.
  8. Lechner M, Counsell N, Liu J, et al. Anosmia and hyposmia in health-care workers with undiagnosed SARS-CoV-2 infection. Lancet Microbe. 2020 Aug;1(4): e150.
  9. Prajapati DP, Shahrvini B, MacDonald BV, Crawford KL, Lechner M, et al. Association of subjective olfactory dysfunction and 12-item odor identification testing in ambulatory COVID-19 patients. Int Forum Allergy Rhinol. 2020 Sep 10.
  10. Cherry G, Rocke J, Chu M, Liu J, Lechner M, et al. Loss of smell and taste: a new marker of COVID-19? Tracking reduced sense of smell during the coronavirus pandemic using search trends. Expert Rev Anti Infect Ther. 2020 Nov;18(11): 1165-1170.
  11. Lechner M, Patel ZM, Philpott C, Lund VJ. Olfactory Loss of Function as a Possible Symptom of COVID-19. JAMA Otolaryngol Head Neck Surg. 2020 Sep 1;146(9):872-873.
  12. Lechner M, Chandrasekharan D, Jumani K, et al. Anosmia as a presenting symptom of SARS-CoV-2 infection in healthcare workers - A systematic review of the literature, case series, and recommendations for clinical assessment and management. Rhinology. 2020 Aug 1;58(4): 394-399.

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