Making scents of loss of taste in COVID-19: Is self-reported loss of taste due to olfactory dysfunction? A prospective study using psychophysical testing

COVID-19 Oral Sequelae: Persistent Gustatory and Saliva Secretory Dysfunctions after Recovery from COVID-19

Diverse manifestations have been recognized to last for a long time in patients infected with SARS-CoV-2. However, understanding of oral sequelae after recovery from COVID-19 is relatively poor compared to that of oral symptoms in the acute phase of COVID-19 and other COVID-19 sequelae. The aim of the present study was to characterize persistent gustatory and saliva secretory dysfunctions and to speculate on their pathogenic mechanisms. Articles were retrieved by searching scientific databases with a cutoff date of September 30, 2022. The literature search indicated that ageusia/dysgeusia and xerostomia/dry mouth are reported by 1-45% of COVID-19 survivors at follow-ups of 21-365 days and by 2-40% of COVID-19 survivors at follow-ups of 28-230 days, respectively. The prevalence of gustatory sequelae partly depends on difference in ethnicity, gender, age, and disease severity of subjects. Co-occurring gustatory and saliva secretory sequelae are pathogenically related to either or both of the following: expression of SARS-CoV-2 cellular entry-relevant receptors in taste buds and salivary glands, and SARS-CoV-2 infection-induced deficiency in zinc that is essential for normality of taste perception and saliva secretion. Given the long-term oral sequelae, hospital discharge is not the end of the disease; therefore, careful attention should be continuously paid to oral conditions of post-COVID-19 patients.

Physiology of the tongue with emphasis on taste transduction

The tongue is a complex multifunctional organ that interacts and senses both interoceptively and exteroceptively. Although it is easily visible to almost all of us, it is relatively understudied and what is in the literature is often contradictory or is not comprehensively reported. The tongue is both a motor and a sensory organ: motor in that it is required for speech and mastication, and sensory in that it receives information to be relayed to the central nervous system pertaining to the safety and quality of the contents of the oral cavity. Additionally, the tongue and its taste apparatus form part of an innate immune surveillance system. For example, loss or alteration in taste perception can be an early indication of infection as became evident during the present global SARS-CoV-2 pandemic. Here, we particularly emphasize the latest updates in the mechanisms of taste perception, taste bud formation and adult taste bud renewal, and the presence and effects of hormones on taste perception, review the understudied lingual immune system with specific reference to SARS-CoV-2, discuss nascent work on tongue microbiome, as well as address the effect of systemic disease on tongue structure and function, especially in relation to taste.

Covid-19 affects taste independently of smell: results from a combined chemosensory home test and online survey from a global cohort (N=10,953)

People often confuse smell loss with taste loss, so it is unclear how much gustatory function is reduced in patients self-reporting taste loss. Our pre-registered cross-sectional study design included an online survey in 12 languages with instructions for self-administering chemosensory tests with ten household items. Between June 2020 and March 2021, 10,953 individuals participated. Of these, 3,356 self-reported a positive and 602 a negative COVID-19 diagnosis (COVID+ and COVID-, respectively); 1,267 were awaiting test results (COVID?). The rest reported no respiratory illness and were grouped by symptoms: sudden smell/taste changes (STC, N=4,445), other symptoms excluding smell or taste loss (OthS, N=832), and no symptoms (NoS, N=416). Taste, smell, and oral irritation intensities and self-assessed abilities were rated on visual analog scales. Compared to the NoS group, COVID+ was associated with a 21% reduction in taste (95% Confidence Interval (CI): 15-28%), 47% in smell (95%-CI: 37-56%), and 17% in oral irritation (95%-CI: 10-25%) intensity. In all groups, perceived intensity of smell (r=0.84), taste (r=0.68), and oral irritation (r=0.37) was correlated. Our findings suggest most reports of taste dysfunction with COVID-19 were genuine and not due to misinterpreting smell loss as taste loss (i.e., a classical taste-flavor confusion). Assessing smell and taste intensity of household items is a promising, cost-effective screening tool that complements self-reports and helps to disentangle taste loss from smell loss. However, it does not replace standardized validated psychophysical tests.

Taste loss as a distinct symptom of COVID-19: a systematic review and meta-analysis

Chemosensory scientists have been skeptical that reports of COVID-19 taste loss are genuine, in part because before COVID-19 taste loss was rare and often confused with smell loss. Therefore, to establish the predicted prevalence rate of taste loss in COVID-19 patients, we conducted a systematic review and meta-analysis of 376 papers published in 2020-2021, with 235 meeting all inclusion criteria. Drawing on previous studies and guided by early meta-analyses, we explored how methodological differences (direct vs. self-report measures) may affect these estimates. We hypothesized that direct measures of taste are at least as sensitive as those obtained by self-report and that the preponderance of evidence confirms taste loss is a symptom of COVID-19. The meta-analysis showed that, among 138,015 COVID-19-positive patients, 36.62% reported taste dysfunction (95% confidence interval: 33.02%-40.39%), and the prevalence estimates were slightly but not significantly higher from studies using direct (n = 15) versus self-report (n = 220) methodologies (Q = 1.73, df = 1, P = 0.1889). Generally, males reported lower rates of taste loss than did females, and taste loss was highest among middle-aged adults. Thus, taste loss is likely a bona fide symptom of COVID-19, meriting further research into the most appropriate direct methods to measure it and its underlying mechanisms.

Covid-19 affects taste independent of taste-smell confusions: results from a combined chemosensory home test and online survey from a large global cohort

People often confuse smell loss with taste loss, so it is unclear how much gustatory function is reduced in patients self-reporting taste loss. Our pre-registered cross-sectional study design included an online survey in 12 languages with instructions for self-administering chemosensory tests with 10 household items. Between June 2020 and March 2021, 10,953 individuals participated. Of these, 5,225 self-reported a respiratory illness and were grouped based on their reported COVID test results: COVID-positive (COVID+, N = 3,356), COVID-negative (COVID-, N = 602), and COVID unknown for those waiting for a test result (COVID?, N = 1,267). The participants who reported no respiratory illness were grouped by symptoms: sudden smell/taste changes (STC, N = 4,445), other symptoms excluding smell or taste changes (OthS, N = 832), and no symptoms (NoS, N = 416). Taste, smell, and oral irritation intensities and self-assessed abilities were rated on visual analog scales. Compared to the NoS group, COVID+ was associated with a 21% reduction in taste (95% confidence interval (CI): 15-28%), 47% in smell (95% CI: 37-56%), and 17% in oral irritation (95% CI: 10-25%) intensity. There were medium to strong correlations between perceived intensities and self-reported abilities (r = 0.84 for smell, r = 0.68 for taste, and r = 0.37 for oral irritation). Our study demonstrates that COVID-19-positive individuals report taste dysfunction when self-tested with stimuli that have little to none olfactory components. Assessing the smell and taste intensity of household items is a promising, cost-effective screening tool that complements self-reports and may help to disentangle taste loss from smell loss. However, it does not replace standardized validated psychophysical tests.

Olfactory and gustatory disorders in COVID-19

Loss of olfaction is one of the symptoms most commonly reported by patients with coronavirus disease 2019 (COVID-19). Although the spontaneous recovery rate is high, recent studies have shown that up to 7% of patients remain anosmic for more than 12 months after the onset of infection, leaving millions of people worldwide suffering from severe olfactory impairment. Olfactory training remains the first recommended treatment. With the continued lack of approved drug treatments, new therapeutic options are being explored. This article reviews the current state of science on COVID-19-related olfactory disorders, focusing on epidemiology, pathophysiology, cure rates, currently available treatment options, and research on new treatments.

COVID-19 Induced Taste Dysfunction and Recovery: Association with Smell Dysfunction and Oral Health Behaviour

Background and Objectives: Disruption to taste and smell are common symptoms of COVID-19 infection. The current literature overlooks taste symptoms and tends to focus on the sense of smell. Persisting cases (>28 days) of taste dysfunction are increasingly recognised as a major future healthcare challenge. This study focuses on the severity and recovery of COVID-19 induced taste loss and association with olfactory symptoms, lifestyle and oral health factors. Materials and Methods: This study was a cross-sectional survey comparing 182 rapid taste recovery participants (≤28 days) with 47 participants with prolonged taste recovery >28 days. Analyses of taste loss in association with smell loss, age, sex, illness severity, diet, BMI, vitamin-D supplementation, antidepressants, alcohol use, smoking, brushing frequency, flossing, missing teeth, appliances and number of dental restorations were conducted. Differences in the severity of the loss of sour, sweet, salt, bitter and umami tastes were explored. Results: Both the severity and the duration of taste and smell loss were closely correlated (p < 0.001). Salt taste was significantly less affected than all other taste qualities (p < 0.001). Persisting taste loss was associated with older age (mean ± 95% CI = 31.73 ± 1.23 years vs. 36.66 ± 3.59 years, p < 0.001) and reduced likelihood of using floss (odds ratio ± 95% CI = 2.22 (1.15−4.25), p = 0.047). Conclusions: Smell and taste loss in COVID-19 are closely related, although a minority of individuals can experience taste or smell dysfunction in the absence of the other. The taste of salt may be less severely affected than other taste qualities and future work exploring this finding objectively is indicated. The association of flossing with rapid taste recovery adds to the growing evidence of a link between good periodontal health and favourable COVID-19 outcomes.

Persisting olfactory dysfunction in post-COVID-19 is associated with gustatory impairment: Results from chemosensitive testing eight months after the acute infection

Olfactory and gustatory disorders are prominent symptoms of acute COVID-19. Although both senses recover in many patients within weeks to months, persistency has been described in up to 60%. However up to now most reports on the course of chemosensitive disorders after COVID-19 are not based on psychophysical testing but only on subjective patients' ratings. In this study we assessed both olfaction and gustation using psychophysical tests eight months after COVID-19. Validated psychophysical testing revealed hyposmia in 18% and hypogeusia in even 32% of 303 included patients. This shows that olfactory and especially gustatory disorders have to be seen as important chronic symptoms post-COVID-19. The high prevalence of gustatory dysfunction indicates that gustatory function does not recover or might even deteriorate in the months following the acute infection.

Results from psychophysical tests of smell and taste during the course of SARS-CoV-2 infection: a review

Only a few studies have assessed smell and taste in Coronavirus Disease 2019 (COVID-19) patients with psychophysical tests, while the majority performed self-rating evaluations. Given the heterogeneity of the published literature, the aim of this review was to systematically analyse the articles on this topic with a focus on psychophysical testing. A search on PubMed and Web of Science from December 2019, to November 2021, with cross-references, was executed. The main eligibility criteria were English-language articles, investigating the clinical features of olfaction and gustation in COVID-19 patients using self-rating assessment, psychophysical testing and imaging techniques. A total of 638 articles were identified and 66 were included. Self-rating assessment was performed in 31 studies, while psychophysical testing in 30 and imaging techniques in 5. The prevalence of chemosensory dysfunction was the most investigated topic, followed by the recovery time. About the psychophysical assessment, the extended version of the Sniffin’ Sticks was used in 11 articles and the Connecticut Chemosensory Clinical Research Center test in another 11. The olfactory threshold performance was the most impacted compared to the discrimination and identification capacities in accordance with the hypothesis of a tropism of SARS-CoV-2 for the olfactory mucosa. The timing significantly influenced the results of the psychophysical testing with 20% of patients presenting olfactory dysfunction at one month after infection.

Gustatory Function in Acute COVID ‐19 ‐ Results from Home‐Based Psychophysical Testing

Objective

Gustatory function during COVID‐19 is self‐reported by around 50% of patients. However, only a few studies assessed gustation using psychophysical testing during acute infection. The objective of this study is to test gustatory function on threshold tests in the very first days of COVID‐19.

Methods

Psychophysical testing consisted of validated and blinded tests for olfaction (NHANES Pocket Smell Test) and gustation (Taste Strips Test). These test kits were sent to home‐quarantined patients and self‐administered using a detailed instruction sheet.

Results

A total of 51 patients were included in this study. Testing was performed 6.5 ± 2.7 days after sampling of respiratory swabs. At this time 37% of patients stated to currently experience a gustatory impairment. The mean Taste Strips score was 10.0 ± 3.4 with 28% scoring in the range of hypogeusia. Interestingly, no significant difference in the results of gustatory testing could be observed between the group with subjectively preserved gustation and the group with self‐rated taste impairment.

Conclusion

During the very first days of COVID‐19, psychophysical gustatory testing revealed hypogeusia in 28%. This is far lower than patients' self‐reports. Different from previous studies, we did not find clear evidence for an impairment of only certain taste qualities.

Level of Evidence

3 Laryngoscope, 132:1082–1087, 2022

The Effects of Persistent Olfactory and Gustatory Dysfunctions on Quality of Life in Long-COVID-19 Patients

(1) Background: Persistent olfactory (POD) and gustatory (PGD) dysfunctions are one of the most frequent symptoms of long-Coronavirus Disease 2019 but their effect on the quality of life (QoL) of patients is still largely unexplored. (2) Methods: An online survey was administered to individuals who reported to have had SARS-CoV-2 infection at least 6 months prior with persisting COVID-19 symptoms (using the COVID symptom index), including ratings of POD and PGD, and their physical (PCS) and mental (MCS) components of quality of life were assessed using the standardized short form 12 questionnaire (SF-12). (3) Results: Responses from 431 unique individuals were included in the analyses. The most frequent persistent symptoms were: fatigue (185 cases, 42.9%), olfactory dysfunction (127 cases, 29.5%), gustatory dysfunction (96 cases, 22.3%) and muscle pain (83 cases, 19.3%). Respondents who reported persisting muscle pain, joint pain, fatigue, headache, gastrointestinal disturbances, and dyspnea had significantly worse PCS. Those experiencing persistent fatigue and dyspnea also showed significantly lower MCS. Respondents reporting POD or PGD showed significantly worse QoL, but only pertaining to the MCS. Multiple regressions predicted MCS based on olfactory and marginally on gustatory ratings, but not PCS. Age significantly affected the prediction of PCS but not MCS, and gender and temporal distance from the COVID-19 diagnosis had no effect. (4) Conclusions: POD and PGD are frequent symptoms of the long-COVID-19 syndrome and significantly reduce QoL, specifically in the mental health component. This evidence should stimulate the establishment of appropriate infrastructure to support individuals with persistent CD, while research on effective therapies scales up.

Taste loss as a distinct symptom of COVID-19: a systematic review and meta-analysis

Chemosensory scientists have been skeptical that reports of COVID-19 taste loss are genuine, in part because before COVID-19 taste loss was rare and often confused with smell loss. Therefore, to establish the predicted prevalence rate of taste loss in COVID-19 patients, we conducted a systematic review and meta-analysis of 376 papers published in 2020-2021, with 241 meeting all inclusion criteria. Drawing on previous studies and guided by early meta-analyses, we explored how methodological differences (direct vs. self-report measures) may affect these estimates. We hypothesized that direct measures of taste are at least as sensitive as those obtained by self-report and that the preponderance of evidence confirms taste loss is a symptom of COVID-19. The meta-analysis showed that, among 138,897 COVID-19-positive patients, 39.2% reported taste dysfunction (95% confidence interval: 35.34%-43.12%), and the prevalence estimates were slightly but not significantly higher from studies using direct (n = 18) versus self-report (n = 223) methodologies (Q = 0.57, df = 1, P = 0.45). Generally, males reported lower rates of taste loss than did females, and taste loss was highest among middle-aged adults. Thus, taste loss is likely a bona fide symptom of COVID-19, meriting further research into the most appropriate direct methods to measure it and its underlying mechanisms.

Störungen des Riech- und Schmeckvermögens bei COVID-19

Der Verlust des Riechvermögens ist eines der Symptome, die von Patienten mit COVID-19 mit am häufigsten angegeben werden. Obwohl die Spontanheilungsrate hoch ist, haben neuere Studien gezeigt, dass bis zu 7 % der Patienten mehr als zwölf Monate nach Beginn der Infektion anosmisch bleiben, sodass weltweit Millionen von Menschen unter schweren Riechstörungen leiden. Riechtraining ist nach wie vor die erste empfohlene Behandlungsform. Angesichts weiterhin fehlender zugelassener medikamentöser Behandlungsmöglichkeiten werden neue therapeutische Optionen erforscht.

Dieser Artikel gibt einen Überblick über den aktuellen Stand der Wissenschaft zu COVID-19-bedingten Riechstörungen, wobei der Schwerpunkt auf der Epidemiologie, der Pathophysiologie, den Heilungsraten, den derzeit verfügbaren Behandlungsmöglichkeiten und der Forschung zu neuen Behandlungsmethoden liegt.

Zitierweise: Klimek L, Hagemann J, Döge J, Freudelsperger L, Cuevas M, Klimek F, Hummel T. Olfactory and gustatory disorders in COVID-19. Allergo J Int 2022;31:243-50

https://doi.org/10.1007/s40629-022-00216-7

Self-reported olfactory and gustatory dysfunction and psychophysical testing in screening for Covid-19: A systematic review and meta-analysis

Background

A substantial proportion of coronavirus disease‐2019 (COVID‐19) patients demonstrate olfactory and gustatory dysfunction (OGD). Self‐reporting for OGD is widely used as a predictor of COVID‐19. Although psychophysical assessment is currently under investigation in this role, the sensitivity of these screening tests for COVID‐19 remains unclear. In this systematic review we assess the sensitivity of self‐reporting and psychophysical tests for OGD.

Methods

A systematic search was performed on PubMed, EMBASE, and ClinicalTrials.gov from inception until February 16, 2021. Studies of suspected COVID‐19 patients with reported smell or taste alterations were included. Data were pooled for meta‐analysis. Sensitivity, specificity, and diagnostic odds ratio (DOR) were reported in the outcomes.

Results

In the 50 included studies (42,902 patients), self‐reported olfactory dysfunction showed a sensitivity of 43.9% (95% confidence interval [CI], 37.8%‐50.2%), a specificity of 91.8% (95% CI, 89.0%‐93.9%), and a DOR of 8.74 (95% CI, 6.67‐11.46) for predicting COVID‐19 infection. Self‐reported gustatory dysfunction yielded a sensitivity of 44.9% (95% CI, 36.4%‐53.8%), a specificity of 91.5% (95% CI, 87.7%‐94.3%), and a DOR of 8.83 (95% CI, 6.48‐12.01). Olfactory psychophysical tests analysis revealed a sensitivity of 52.8% (95% CI, 25.5%‐78.6%), a specificity of 88.0% (95% CI, 53.7%‐97.9%), and a DOR of 8.18 (95% CI, 3.65‐18.36). One study used an identification test for gustatory sensations assessment.

Conclusion

Although demonstrating high specificity and DOR values, neither self‐reported OGD nor unvalidated and limited psychophysical tests were sufficiently sensitive in screening for COVID‐19. They were not suitable adjuncts in ruling out the disease.

Taste loss as a distinct symptom of COVID-19: A systematic review and meta-analysis

Chemosensory scientists have been skeptical that reports of COVID-19 taste loss are genuine, in part because before COVID-19, taste loss was rare and often confused with smell loss. Therefore, to establish the predicted prevalence rate of taste loss in COVID-19 patients, we conducted a systematic review and meta-analysis of 376 papers published in 2020-2021, with 241 meeting all inclusion criteria. Additionally, we explored how methodological differences (direct vs. self-report measures) may affect these estimates. We hypothesized that direct prevalence measures of taste loss would be the most valid because they avoid the taste/smell confusion of self-report. The meta-analysis showed that, among 138,897 COVID-19-positive patients, 39.2% reported taste dysfunction (95% CI: 35.34-43.12%), and the prevalence estimates were slightly but not significantly higher from studies using direct (n = 18) versus self-report (n = 223) methodologies (Q = 0.57, df = 1, p = 0.45). Generally, males reported lower rates of taste loss than did females and taste loss was highest in middle-aged groups. Thus, taste loss is a bona fide symptom COVID-19, meriting further research into the most appropriate direct methods to measure it and its underlying mechanisms.