Prevalence of olfactory dysfunction and quality of life in hospitalised patients 1 year after SARS-CoV-2 infection: a cohort study

Receptors Involved in COVID-19-Related Anosmia: An Update on the Pathophysiology and the Mechanistic Aspects

Olfactory perception is an important physiological function for human well-being and health. Loss of olfaction, or anosmia, caused by viral infections such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has received considerable attention, especially in persistent cases that take a long time to recover. This review discusses the integration of different components of the olfactory epithelium to serve as a structural and functional unit and explores how they are affected during viral infections, leading to the development of olfactory dysfunction. The review mainly focused on the role of receptors mediating the disruption of olfactory signal transduction pathways such as angiotensin converting enzyme 2 (ACE2), transmembrane protease serine type 2 (TMPRSS2), neuropilin 1 (NRP1), basigin (CD147), olfactory, transient receptor potential vanilloid 1 (TRPV1), purinergic, and interferon gamma receptors. Furthermore, the compromised function of the epithelial sodium channel (ENaC) induced by SARS-CoV-2 infection and its contribution to olfactory dysfunction are also discussed. Collectively, this review provides fundamental information about the many types of receptors that may modulate olfaction and participate in olfactory dysfunction. It will help to understand the underlying pathophysiology of virus-induced anosmia, which may help in finding and designing effective therapies targeting molecules involved in viral invasion and olfaction. To the best of our knowledge, this is the only review that covered all the receptors potentially involved in, or mediating, the disruption of olfactory signal transduction pathways during COVID-19 infection. This wide and complex spectrum of receptors that mediates the pathophysiology of olfactory dysfunction reflects the many ways in which anosmia can be therapeutically managed.

Impaired metal perception and regulation of associated human foliate papillae tongue transcriptome in long-COVID-19

Chemosensory impairment is an outstanding symptom of SARS-CoV-2 infections. We hypothesized that measured sensory impairments are accompanied by transcriptomic changes in the foliate papillae area of the tongue. Hospital personnel with known SARS-CoV-2 immunoglobulin G (IgG) status completed questionnaires on sensory perception (n = 158). A subcohort of n = 141 participated in forced choice taste tests, and n = 43 participants consented to donate tongue swabs of the foliate papillae area for whole transcriptome analysis. The study included four groups of participants differing in IgG levels (≥ 10 AU/mL = IgG+; < 10 AU/mL = IgG-) and self-reported sensory impairment (SSI±). IgG+ subjects not detecting metallic taste had higher IgG+ levels than IgG+ participants detecting iron gluconate (p = 0.03). Smell perception was the most impaired biological process in the transcriptome data from IgG+/SSI+ participants subjected to gene ontology enrichment. IgG+/SSI+ subjects demonstrated lower expression levels of 166 olfactory receptors (OR) and 9 taste associated receptors (TAS) of which OR1A2, OR2J2, OR1A1, OR5K1 and OR1G1, as well as TAS2R7 are linked to metallic perception. The question raised by this study is whether odorant receptors on the tongue (i) might play a role in metal sensation, and (ii) are potential targets for virus-initiated sensory impairments, which needs to be investigated in future functional studies.

Olfactory immunology: the missing piece in airway and CNS defence

The olfactory mucosa is a component of the nasal airway that mediates the sense of smell. Recent studies point to an important role for the olfactory mucosa as a barrier to both respiratory pathogens and to neuroinvasive pathogens that hijack the olfactory nerve and invade the CNS. In particular, the COVID-19 pandemic has demonstrated that the olfactory mucosa is an integral part of a heterogeneous nasal mucosal barrier critical to upper airway immunity. However, our insufficient knowledge of olfactory mucosal immunity hinders attempts to protect this tissue from infection and other diseases. This Review summarizes the state of olfactory immunology by highlighting the unique immunologically relevant anatomy of the olfactory mucosa, describing what is known of olfactory immune cells, and considering the impact of common infectious diseases and inflammatory disorders at this site. We will offer our perspective on the future of the field and the many unresolved questions pertaining to olfactory immunity.

Postinfectious conditions challenge disease-specificity of SNOT-22

PURPOSE

The Sino-Nasal-Outcome-Test 22 (SNOT-22) questionnaire assesses treatment outcome and health-related quality of life (HRQOL) in patients with chronic rhinosinusitis (CRS). However, given the overlap between CRS and olfaction in terms of nasal function and the definition of CRS, a fundamental question arises: can patients with olfactory dysfunction (OD) stemming from other causes attain SNOT-22 scores similar to those seen in CRS, even in the absence of CRS? Our study aimed to explore whether OD arising from various postinfectious mechanisms challenges the disease-specificity of SNOT-22 for CRS. If so, could focus on scores within specific symptom domains of SNOT-22 prove valuable in distinguishing between different etiologies.

METHODS

The study adopted an observational, retrospective cohort design based on prospectively registered patients and related variables using the REDCap platform. 460 patients experiencing OD due to either (1) simple or (2) complex post-COVID-19, (3) postinfectious non-COVID-19, and (4) CRS, were included in the analysis.

RESULTS

The study revealed that the total SNOT-22 score lacks disease-specificity for CRS. This is evident, because complex postinfectious mechanisms resulting from COVID-19 can produce similar symptoms in patients. Notably, elevated total scores were primarily driven by high subdomain scores within the "sleep and cognition" domain.

CONCLUSIONS

The application of SNOT-22 as a screening tool needs to be approached with caution, as the total score alone does not provide disease-specific insights. A more thorough exploration of the four symptom domains and the identification of distinctive scoring patterns within the clinical context may prove pivotal in effectively differentiating between various underlying causes.

Persistent Smell Disorders After COVID-19 Infection and Their Impact on Quality of Life

Background The COVID-19 pandemic has led to various health challenges, including the disruption of people's sense of smell. Olfactory disorders have been reported as a lingering consequence of COVID-19, with diverse patterns of smell dysfunction experienced by patients. Objectives This study aimed to investigate the impact of persistent smell disorders on the quality of life of individuals who recovered from COVID-19 in Taif, Saudi Arabia. Methodology A descriptive cross-sectional study was conducted in Taif, Saudi Arabia, between October 2023 and January 2024. The study included adults with a history of PCR-confirmed COVID-19 infection in Taif city. Data were collected using a validated online survey employing a convenience sampling technique. Statistical analysis was carried out using IBM SPSS Statistics for Windows, Version 26.0 (Released 2019; IBM Corp., Armonk, New York, United States), and chi-squared tests were used to assess the relationships. Results The study included 429 participants. A total of 52.7% of the respondents reported a loss of smell after recovering from COVID-19, and 14.9% reported a persistent loss of their sense of smell. The most common types of smell disorders experienced were hyposmia, anosmia, and parosmia. The study revealed emotional distress, changes in eating habits, and social impact among participants with smell disorders. Conclusion This study highlights the high prevalence of persistent smell disorders among individuals who recovered from COVID-19 in Taif, Saudi Arabia. The findings emphasize the complex nature of these disorders and their impact on patients' quality of life. This study contributes valuable information that can inform healthcare practices and support services for individuals experiencing post-COVID-19 smell disorders.

Type 2 and Non-type 2 Inflammation in the Upper Airways: Cellular and Molecular Alterations in Olfactory Neuroepithelium Cell Populations

PURPOSE OF REVIEW

Neurogenesis occurring in the olfactory epithelium is critical to continuously replace olfactory neurons to maintain olfactory function, but is impaired during chronic type 2 and non-type 2 inflammation of the upper airways. In this review, we describe the neurobiology of olfaction and the olfactory alterations in chronic rhinosinusitis with nasal polyps (type 2 inflammation) and post-viral acute rhinosinusitis (non-type 2 inflammation), highlighting the role of immune response attenuating olfactory neurogenesis as a possibly mechanism for the loss of smell in these diseases.

RECENT FINDINGS

Several studies have provided relevant insights into the role of basal stem cells as direct participants in the progression of chronic inflammation identifying a functional switch away from a neuro-regenerative phenotype to one contributing to immune defense, a process that induces a deficient replacement of olfactory neurons. The interaction between olfactory stem cells and immune system might critically underlie ongoing loss of smell in type 2 and non-type 2 inflammatory upper airway diseases. In this review, we describe the neurobiology of olfaction and the olfactory alterations in type 2 and non-type 2 inflammatory upper airway diseases, highlighting the role of immune response attenuating olfactory neurogenesis, as a possibly mechanism for the lack of loss of smell recovery.

Impact of post-COVID-19 olfactory disorders on quality of life, hedonic experiences and psychiatric dimensions in general population

BACKGROUND AND OBJECTIVE

Olfactory disorders in COVID-19 impact quality of life and may lead to psychological impairments. Prevalence ranges from 8 to 85%, persisting in about 30% of cases. This study aimed to evaluate the 6-month post-COVID-19 impact on quality of life, hedonic experiences, anxiety and depression due to olfactory disorders. Additionally, it sought to compare psychophysical tests and self-perceived olfactory evaluations.

METHODS

A prospective, longitudinal study was conducted over baseline (T0) and 6 months (T1) on individuals with persistent olfactory disorders post-COVID-19 for more than 6 weeks. Psychophysical tests employed the Sniffin' Sticks Test® (TDI score), and self-perceived olfactory evaluation used a Visual Analogue Scale. Quality of life was assessed with an Olfactive Disorder Questionnaire and the French version of the Quality of Life and Diet Questionnaire. Hedonic experiences were gauged using the Snaith-Hamilton Pleasure Scale, while anxiety and depression dimensions were measured by The State-Trait Anxiety Inventory, The Post Traumatic Stress Checklist Scale, and Hamilton Rating Scale for Depression. Participants were classified into the "normosmic group" (NG) and the "olfactory disorders group" (ODG) at T0 and T1 based on the TDI score.

RESULTS

Were included 56 participants (58.93% women, 41.07% men) with a mean age of 39.04 years and a mean duration of post-COVID-19 olfactory disorders of 5.32 months. At T1, ODG had a significantly lower quality of life and hedonic experiences than NG. No significant differences in anxiety and depression dimensions were observed between groups. At T0, psychophysical tests and self-perceived olfactory evaluations were significantly correlated with quality of life and hedonic experiences in both groups. At T1, self-perceived olfactory evaluation in NG correlated significantly with quality of life, hedonic experiences, anxiety and depression dimensions, whereas ODG only correlated with hedonic experiences.

CONCLUSION

Individuals with persistent post-COVID-19 olfactory disorders after six months demonstrated compromised quality of life and hedonic experiences. Self-perceived olfactory evaluation played a more significant role in influencing quality of life and the dimension of anxiety and depression than the psychophysical presence of olfactory disorders. These findings emphasize the importance of considering patients' perceptions to comprehensively assess the impact of olfactory disorders on their well-being.

TRIAL REGISTRATION

ClinicalTrials.gov number (ID: NCT04799977).

Olfactory immune response to SARS-CoV-2

Numerous pathogens can infect the olfactory tract, yet the pandemic caused by SARS-CoV-2 has strongly emphasized the importance of the olfactory mucosa as an immune barrier. Situated in the nasal passages, the olfactory mucosa is directly exposed to the environment to sense airborne odorants; however, this also means it can serve as a direct route of entry from the outside world into the brain. As a result, olfactotropic infections can have serious consequences, including dysfunction of the olfactory system, CNS invasion, dissemination to the lower respiratory tract, and transmission between individuals. Recent research has shown that a distinctive immune response is needed to protect this neuronal and mucosal tissue. A better understanding of innate, adaptive, and structural immune barriers in the olfactory mucosa is needed to develop effective therapeutics and vaccines against olfactotropic microbes such as SARS-CoV-2. Here, we summarize the ramifications of SARS-CoV-2 infection of the olfactory mucosa, review the subsequent immune response, and discuss important areas of future research for olfactory immunity to infectious disease.

Investigating the Interplay between Olfaction, Social Behaviour, and Individual Differences: Editorial

Long-COVID mercilessly brought awareness to what olfaction researchers have known all along; losing your sense of smell changes your experiences with the world around you and can compromise your health and wellbeing [...].

Looking at the Data on Smoking and Post-COVID-19 Syndrome-A Literature Review

Long COVID is a recently described entity that is responsible for significant morbidity and that has consequences ranging from mild to life-threatening. The underlying mechanisms are not completely understood, and treatment options are currently limited, as existing data focus more on risk factors and predictors. Smoking has been reported as a risk factor for poor outcomes of acute SARS-CoV-2 infection and seems to also play a role in mediating post-COVID-19 symptoms. We aimed to review relevant work addressing the interaction between smoking and long COVID in order to characterize smoking's role as a risk factor and possibly identify new research directions. Methods: The PubMed/MEDLINE database was searched using the keywords 'smoking', 'long COVID', and 'post-acute COVID' to identify relevant English-language articles published up to October 2023. Results and conclusions: From the 374 initial hits, a total of 36 papers were deemed relevant to the aim of the review. There was significant variability concerning the ways in which tobacco usage was quantified and reported; still, there is compelling evidence linking smoking to an increased risk of developing manifestations of post-acute-COVID disease. Some clinical conditions, such as dyspnea, cardiovascular symptoms, and cognitive or mental-health impairment, seem to be relatively strongly associated with smoking, while the connection between smoking and upper-airway involvement seems less certain. The available data support recommending smoking cessation as a clinical tool for the prevention of long COVID.

Prevalence of taste and smell dysfunction in mild and asymptomatic COVID-19 patients during Omicron prevalent period in Shanghai, China: a cross-sectional survey study

OBJECTIVES

COVID-19, which is caused by SARS-CoV-2, is a severe threat to human health and the economy globally. This study aimed to investigate the prevalence of taste and/or smell dysfunction and associated risk factors in mild and asymptomatic patients with Omicron infection in Shanghai, China.DesignThis was a questionnaire-based cross-sectional study.

SETTING

COVID-19 patients at the makeshift hospital in the Shanghai World Expo Exhibition and Convention Centre were recruited from March to April 2022.

PARTICIPANTS

In total, 686 COVID-19-infected patients who were defined as mild or asymptomatic cases according to the diagnostic criteria of New Coronavirus Pneumonia Prevention and Control Programme ninth edition (National Health Commission of China, 2022) were enrolled.

MEASURES

Data to investigate taste and smell loss and to characterise other symptoms were collected by the modified Chemotherapy-induced Taste Alteration Scale and Sino-Nasal Outcome Test-22 questionnaires. The risk factors for the severity of taste/smell dysfunction were analysed by binary logistic regression models.

RESULTS

379 males (379/686, 55.2%) and 307 females (307/686, 44.8%) completed the questionnaires to record recent changes in taste and smell ability. A total of 302 patients (44%) had chemosensory dysfunction with Omicron infection, of which 22.7% (156/686) suffered from both taste and smell dysfunction. In addition, cough (60.2%), expectoration (40.5%), fever (33.2%) and sore throat (32.5%) were common symptoms during Omicron infection. The quality-of-life-related indicators were negatively associated with participants' self-reported taste and smell dysfunction.

CONCLUSIONS

The prevalence of taste or/and smell dysfunction in patients with Omicron infections was 44%. Individuals with chemosensory dysfunction had significantly higher rates of various upper respiratory influenza-like symptoms, xerostomia and bad breath. Moreover, smell dysfunction was a risk factor for the prevalence of taste dysfunction in patients with Omicron infection.

TRIAL REGISTRATION NUMBER

ChiCTR 2200059097.

The Correlation between the Results of the Sniffin' Sticks Test, Demographic Data, and Questionnaire of Olfactory Disorders in a Hungarian Population after a SARS-CoV-2 Infection

BACKGROUND

After a severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection, smell disorders frequently occur, significantly affecting patients' quality of life (QoL).

METHODS

110 patients with persistent olfactory disorder after coronavirus infection were enrolled. These patients underwent chemosensory testing using the Sniffin' Sticks test, and completed the Questionnaire of Olfactory Disorders (QOD).

RESULTS

30% of the patients reported anosmia, and 70% reported hyposmia. Upon comparing subjective and chemosensory testing categories, good category matching was observed in 75.3% (i.e., anosmia based on both methods in 10 and hyposmia in 48 cases). Statistical analysis using the Chi-square test revealed a significant result (p = 0.001 *). Between the TDI (i.e., Threshold, Discrimination, Identification) results of the three subjective report groups (i.e., hyposmia, anosmia, and parosmia), no significant differences were observed. When the TDI and QOD results were compared, no consistent significant correlations were found in most TDI and QOD outcomes. Between the TDI and Scale 2 results, a significant, although slight correlation was observed by the Spearman's (rho = 0.213, p = 0.027 *) and Pearson's (rho = 0.201, p = 0.037 *) tests.

CONCLUSIONS

The nonsignificant correlation between objective and subjective methods suggests that these results should be interpreted independently. Moreover, adequate management is essential even in mild cases.

Long-term Consequences of COVID-19: Chemosensory Disorders

PURPOSE OF REVIEW

A number of sequelae after acute coronavirus disease 2019 (COVID-19) significantly affect the quality of life of patients. The chemosensory disorders including olfactory dysfunction (OD) and gustatory dysfunction (GD) are two of the commonest symptoms complained by patients with COVID-19. Although chemosensory function has been reported improved in over 60% of COVID-19 patients in a short time after acute infection, it may last as a major symptom for patients with long COVID-19. This narrative review discussed current literatures on OD and GD in long COVID-19 including the prevalence, risk factors, possible mechanisms, and potential therapies.

RECENT FINDINGS

Although the prevalence of OD and GD has declined continuously after acute COVID-19, a considerable number of patients had persistent chemosensory disorders 3 months to 2 years after symptom onset. Female gender, initial severity of dysfunction, nasal congestion, emotional distress and depression, and SARS-CoV-2 variants have been identified as risk factors for persistent OD and GD in long COVID-19. The pathogenesis of OD and GD in long COVID-19 remains unknown, but may be analogous to the persistent OD and GD post common respiratory viral infection. Corticosteroids and olfactory training might be a potential choice regarding the treatment of lasting OD and GD after SARS-CoV-2 infection; however, more studies are needed to prove it. OD and GD are common long-term consequences of COVID-19 and influenced by gender, initial severity of dysfunction, emotional distress and depression, and SARS-CoV-2 variants. More studies are needed to illustrate their pathogenesis and to establish therapeutic strategies.

Subjective and psychophysical olfactory and gustatory dysfunction among COVID-19 outpatients; short- and long-term results

BACKGROUND

Olfactory and gustatory dysfunctions are early symptoms of SARS-CoV-2 infection. Between 20-80% of infected individuals report subjective altered sense of smell and/or taste during infection. Up to 2/3 of previously infected experience persistent olfactory and/or gustatory dysfunction after 6 months. The aim of this study was to examine subjective and psychophysical olfactory and gustatory function in non-hospitalized individuals with acute COVID-19 up to 6 months after infection.

METHODS

Individuals aged 18-80-years with a positive SARS-CoV-2 PCR test no older than 10 days, were eligible. Only individuals able to visit the outpatient examination facilities were included. Gustatory function was tested with the Burgharts Taste Strips and olfactory function was examined with the Brief Smell Identifications test (Danish version). Subjective symptoms were examined through an online questionnaire at inclusion, day 30, 90 and 180 after inclusion.

RESULTS

Fifty-eight SARS-CoV-2 positive and 56 negative controls were included. 58.6% (34/58) of SARS-CoV-2 positive individuals vs. 8.9% (5/56) of negative controls reported subjective olfactory dysfunction at inclusion. For gustatory dysfunction, 46.5% (27/58) of positive individuals reported impairment compared to 8.9% (5/56) of negative controls. In psychophysical tests, 75.9% (46/58) had olfactory dysfunction and 43.1% (25/58) had gustatory dysfunction among the SARS-CoV-2 positive individuals at inclusion. Compared to negative controls, SARS-CoV-2 infected had significantly reduced olfaction and gustation. Previously infected individuals continued to report lower subjective sense of smell 30 days after inclusion, whereafter the difference between the groups diminished. However, after 180 days, 20.7% (12/58) positive individuals still reported reduced sense of smell and taste.

CONCLUSION

Olfactory and gustatory dysfunctions are prevalent symptoms of SARS-CoV-2 infection, but there is inconsistency between subjective reporting and psychophysical test assessment of especially olfaction. Most individuals regain normal function after 30 days, but approximately 20% report persistent olfactory and gustatory dysfunction 6 months after infection.

Association between chemosensory dysfunctions and inflammatory biomarkers in patients with SARS-CoV-2 infection: a systematic review and meta-analysis

BACKGROUND

There is evidence that chemosensory dysfunctions, including smell and taste disorders, are common findings in patients with SARS-CoV-2 infection. However, the underlying biological mechanisms and the role of inflammatory markers are still poorly understood.

AIM

To investigate the inflammatory biomarkers levels in patients with COVID-19 presenting chemosensory dysfunctions.

METHODS

This review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. A systematic literature search was performed from January 1, 2020, to May 12, 2022. Observational studies that provided data on hematological, biochemical, infection-related indices and cellular immunity, and coagulation function in patients with COVID-19 experiencing smell and/or taste disorders were considered eligible. Effect sizes were reported as standardized mean difference (SMD) with 95% confidence intervals (CI). A negative effect size indicated that the inflammatory biomarker levels were lower among patients with chemosensory dysfunctions.

RESULTS

Eleven studies were included. Patients with chemosensory disturbances had lower levels of leukocytes (SMD - 0.18, 95% CI - 0.35 to - 0.01, p = 0.04), lactate dehydrogenase (SMD - 0.45, 95% CI - 0.82 to - 0.09, p = 0.01), IL-6 (SMD - 0.25, 95% CI - 0.44 to - 0.06, p < 0.01), and C-reactive protein (SMD - 0.33, 95% CI - 0.58 to - 0.08, p < 0.01) than patients without chemosensory disturbances.

CONCLUSION

Patients with SARS-CoV-2 infection who have olfactory and gustatory disorders have a lower inflammatory response than patients who do not have chemosensory alterations. The presence of these symptoms may indicate a more favorable clinical course for COVID-19.

The Role of Social Media in Improving Patient Recruitment for Research Studies on Persistent Post-Infectious Olfactory Dysfunction

Background and Objectives: Since the COVID-19 pandemic, the number of cases of post-infectious olfactory dysfunction (PIOD) has substantially increased. Despite a good recovery rate, olfactory dysfunction (OD) becomes persistent in up to 15% of cases and further research is needed to find new treatment modalities for those patients who have not improved on currently available treatments. Social media has emerged as a potential avenue for patient recruitment, but its role in recruiting patients with smell dysfunction remains unexplored. We conducted a survey using the AbScent Facebook page to evaluate the feasibility of using this platform for future studies on smell dysfunction. Materials and Methods: Between 26 October and 4 November 2021, we conducted an online survey to evaluate propensity of patients with PIOD who would be willing to participate in research studies on smell dysfunction. Results: Sixty-five subjects were surveyed with a response rate of 90.7%. The median visual analogue scale (VAS) for sense of smell was 0 at infection and 2 at survey completion. The median length of OD was 1.6 years, and the main cause of OD was SARS-CoV-2 (57.6%). Parosmia was reported in 41 subjects (69.5%) whilst phantosmia in 22 (37.3%). The median length of olfactory training (OT) was 6 months but subjectively effective in 15 subjects (25.4%). Twenty-seven subjects (45.8%) tried other medications to improve olfaction, but only 6 participants (22.2%) reported an improvement. All subjects expressed their propensity to participate in future studies with most of them (38; 64.4%) willing to be enrolled either in medical and surgical studies or to be part of a randomised study design (11; 18.6%). Conclusions: Using the AbScent Facebook platform we successfully selected a population of subjects with persistent and severe OD that have failed to improve on available treatments and are willing to participate in further clinical trials.