Assessment of patient recognition of coronavirus disease 2019 (COVID-19)-associated olfactory loss and recovery: a longitudinal study

Comparative analyses of post-infectious olfactory dysfunction between COVID-19 and non-COVID-19 cases

To identify the differences between COVID-19-associated and non-COVID-19-associated olfactory dysfunction (OD), we analyzed demographic and clinical characteristics based on the causative virus (COVID versus non-COVID groups) in patients with post-infectious olfactory dysfunction (PIOD) who underwent the olfactory questionnaire and olfactory function test. Out of 169 patients with PIOD, 99 were diagnosed with COVID-19 (COVID group), while 70 were not (non-COVID group). The COVID group was younger and had a higher percentage of male patients as well as patients with parosmia than the non-COVID group. In the initial olfactory function tests, the TDI, discrimination and identification scores were significantly higher in the COVID group than in the non-COVID group. TDI scores were significantly increased in patients with PIOD after treatment, regardless of the group. The threshold score was significantly increased by 1.38 in the COVID group while the identification score was significantly increased by 2.67 in the non-COVID group. Patients with COVID-19-associated OD were younger in age, tended to be male, had a higher incidence of parosmia, and had better initial olfactory function test results compared to those with non-COVID-19-associated OD. Following treatment, odor detection threshold improved in the COVID group, whereas odor identification improved in the non-COVID group.

[Post-COVID patients with persistent chemosensory symptoms are rare in the general population]

OBJECTIVE

The prevalence of long-/post-COVID-associated chemosensory symptoms is reported in the literature to be significantly higher than clinical reality reflects.

METHODS

1. N= 4062 adults acutely infected with SARS-CoV-2 and their symptoms transmitted by the Jena health office to the Robert Koch Institute between March 2020 and September 2021 were evaluated. 2. Part of the same cohort (N = 909 of 4062) answered an extensive questionnaire at least 3 months after the start of the infection, including existing chemosensory post-COVID-associated complaints. 3. Fourteen post-COVID Jena patients with chemosensory symptoms who had become acutely infected during the same period were diagnosed, treated and advised in our ENT specialist outpatient clinic.

RESULTS

The prevalence of chemosensory symptoms at the onset of infection was 19% (600/3187). About every second written respondent of the formerly acutely infected (441/890) remembered chemosensory symptoms during their COVID-19 infection. Of these, around 38% (167/441) complained of persistent chemosensory post-COVID symptoms after an average of 14.5 months. Only 2.3% (14/600) of the previously acutely infected patients with chemosensory symptoms sought medical help in a special consultation. Quantitative chemosensory damage could only be objectified in half, i.e. 1.2% (7/600) of the total cohort.

CONCLUSIONS

Despite a high prevalence of subjective chemosensory symptoms in acutely and formerly SARS-CoV-2 infected people, there is only a low need for specialized treatment, so that, unlike other post-COVID-associated complaints, the healthcare system as a whole appears to be less significantly burdened.

Effective early strategy to prevent olfactory and gustatory dysfunction in COVID-19: a randomized controlled trial

BACKGROUND

Olfactory and gustatory dysfunctions (OGDs) are key symptoms of coronavirus disease 2019 (COVID-19), which may lead to neurological complications, and lack of effective treatment. This may be because post-disease treatments may be too late to protect the olfactory and gustatory functions.

AIM

To evaluate the effectiveness of early use of saline nasal irrigation (SNI), corticosteroid nasal spray, and saline or chlorhexidine gluconate mouthwash for preventing OGDs in COVID-19.

DESIGN

This study was a double-blind randomized controlled trial.

METHODS

The study was conducted from 5 May to 16 June 2022. We recruited patients from three hospitals who were admitted with COVID-19 but without OGDs on the day of admission. Olfactory and gustatory functions were evaluated using the Taste and Smell Survey and the numerical visual analog scale. Participants were randomized to the saline, drug or control groups. The control group received no intervention, saline group received SNI plus saline nasal spray and mouthwash, and the trial group received SNI plus budesonide nasal spray and chlorhexidine gluconate mouthwash. Participants were assessed again on the day of discharge.

RESULTS

A total of 379 patients completed the trial. The prevalence of OGDs was significantly lower in the saline (11.8%, 95% CI, 6.6-19.0%; P < 0.001) and drug (8.3%, 95% CI, 4.1-14.8%; P < 0.001) groups than in the control group (40.0%, 95% CI, 31.8-48.6%). Additionally, both interventions reduced the severity of OGDs.

CONCLUSIONS

We demonstrated effective strategies for preventing COVID-19-related OGDs, and the findings may guide early management of severe acute respiratory disease coronavirus 2 (SARS-CoV-2) infection to reduce the incidence of COVID-19-related complications.

Recovery rates and long-term olfactory dysfunction following COVID-19 infection

Objectives

Olfactory dysfunction is one of the most recognized symptoms of COVID-19, significantly impacting quality of life, particularly in cases where recovery is prolonged. This review aims to explore patterns of olfactory recovery post-COVID-19 infection, with particular focus on delayed recovery.

Data Sources

Published literature in the English language, including senior author's own work, online and social media platforms, and patients' anecdotal reports.

Method

A comprehensive review of the literature was undertaken by the authors with guidance from the senior author with expertise in the field of olfaction.

Results

Based on self-report, an estimated 95% of patients recover their olfactory function within 6 months post-COVID-19 infection. However, psychophysical testing detects higher rates of persistent olfactory dysfunction. Recovery has been found to continue for at least 2 years postinfection; negative prognostic indicators include severe olfactory loss in the acute phase, female sex, and older age. Variability in quantitative and qualitative disturbance in prolonged cases likely reflects both peripheral and central pathophysiological mechanisms. Limitations of many of the reviewed studies reflect lack of psychophysical testing and baseline olfactory assessment.

Conclusions

Post-COVID-19 olfactory dysfunction remains a significant health and psychosocial burden. Emerging evidence is improving awareness and knowledge among clinicians to better support patients through their olfactory rehabilitation, with hope of recovery after several months or years. Further research is needed to better understand the underlying pathogenesis of delayed recovery, identify at risk individuals earlier in the disease course, and develop therapeutic targets.

Subjective Perception of Recovery and Measured Olfactory Function in COVID-19 Patients

This cross-sectional study aimed to investigate self-rated olfactory dysfunction in relation to measured olfactory function after partial or complete subjective recovery in individuals with a history of coronavirus disease 2019 (COVID-19) infection. A total of 186 individuals (aged 5-62 years) with a history of COVID-19 infection were included. Visual analogue scale (VAS) ratings for olfactory function (before, during, and after infection) and age-appropriate psychophysical olfactory test scores (odor threshold and odor identification: "Sniffin' Sticks" for adults and both "Sniffin' Sticks" and "U-Sniff" for children) were determined. Participants were assigned to four "age groups" and three "recovery classes" (incomplete recovery, complete recovery, no smell loss). Surprisingly, there were no significant differences in odor threshold and adult identification scores between the "recovery classes". However, children with "incomplete recovery" had lower identification scores than those with "complete recovery" (p = 0.033) and those with "no smell loss" (p = 0.022). The pediatric age groups had significantly higher VAS ratings during and after COVID-19 compared to older participants. Older individuals experienced greater magnitude of changes in their sense of smell after COVID-19 infection, but those with parosmia were 3.5 times more likely to report "incomplete recovery" of olfaction after COVID-19. The general prognosis for olfactory recovery after COVID-19 is good but appears to be particularly confounded by the presence of parosmia, leading patients to subjectively report incomplete olfactory recovery. Although it is of high significance to monitor recovery using validated psychophysical olfactory tests, subjective measures of olfaction help provide specific insight, especially for qualitative olfactory dysfunction.

Liu D, A. Müller C, A. Stuck B, Welge-Lüssen A, Hähner A. Olfactory Dysfunction: Etiology, Diagnosis, and Treatment

BACKGROUND

Disorders of the sense of smell have received greater attention because of the frequency with which they occur as a symptom of SARS-CoV-2 infection. Olfactory dysfunction can lead to profound reduction in quality of life and may arise from many different causes.

METHODS

A selective literature review was conducted with consideration of the current version of the guideline issued by the Association of the Scientific Medical Societies in Germany.

RESULTS

The cornerstones of diagnosis are the relevant medical history and psychophysical testing of olfactory function using standardized validated tests. Modern treatment strategies are oriented on the cause of the dysfunction. While treatment of the underlying inflammation takes precedence in patients with sinunasal dysosmia, olfactory training is the primary treatment option for other forms of the disorder. The prognosis is determined not only by the cause of the olfactory dysfunction and the patient's age, but also by the olfactory performance as measured at the time of diagnosis.

CONCLUSION

Options for the treatment of olfactory dysfunction are available but limited, depending on the cause. It is therefore important to carry out a detailed diagnostic work-up and keep the patient informed of the expected course and prognosis.

Use of platelet-rich plasma for COVID-19-related olfactory loss: a randomized controlled trial

INTRODUCTION

The current study evaluated the use of platelet-rich plasma (PRP), an autologous blood product with supraphysiologic concentrations of growth factors, in the treatment of prolonged coronavirus disease 2019 (COVID-19)-related smell loss.

METHODS

This multi-institutional, randomized controlled trial recruited patients with COVID-19 who had objectively measured smell loss (University of Pennsylvania Smell Identification Test [UPSIT] ≤ 33) between 6 and 12 months. Patients were randomized to three intranasal injections of either PRP or sterile saline into their olfactory clefts. The primary outcome measure was change in Sniffin' Sticks score (threshold, discrimination, and identification [TDI]) from baseline. The secondary end point measures included responder rate (achievement of a clinically significant improvement, ≥5.5 points TDI), change in individual TDI olfaction scores, and change in subjective olfaction via a visual analog scale.

RESULTS

A total of 35 patients were recruited and 26 completed the study. PRP treatment resulted in a 3.67-point (95% CI: 0.05-7.29, p = 0.047) greater improvement in olfaction compared with the placebo group at 3 months and a higher response rate (57.1% vs 8.3%, odds ratio 12.5 [95% exact bootstrap confidence interval, 2.2-116.7]). There was a greater improvement in smell discrimination following PRP treatment compared with placebo but no difference in smell identification or threshold. There was no difference in subjective scores between PRP and placebo. No adverse effects were reported.

CONCLUSION

Olfactory function following COVID-19 can improve spontaneously after 6 months and can improve to a greater extent with PRP injection. These data build on the promise of PRP to be a safe potential treatment option for patients with COVID-19-related smell loss, and larger-powered studies will help further assess its efficacy.

Clinical factors associated with lower health scores in COVID-19-related persistent olfactory dysfunction

BACKGROUND

Patients with persistent COVID-19 olfactory dysfunction (OD) commonly report parosmia. Understanding the impact of COVID-19 OD and parosmia is critical to prioritizing research and interventions. In this study we investigate the impact of parosmia and other clinical and disease characteristics on health state utility values (HUVs) for those with persistent COVID-19 OD.

METHODS

Patients with a history of COVID-19 diagnosis and persistent OD were recruited from a tertiary medical center and a social media support forum for chemosensory dysfunction. Clinical characteristics and disease-specific symptoms were obtained along with self-reported history of smell function and presence of parosmia. HUVs were calculated using indirect (EuroQol 5-Dimension [EQ-5D]) and direct (VAS) measures.

RESULTS

Our study included 286 subjects (75.52% women) with persistent COVID-19-related OD. Results (mean ± standard deviation) of HUVs based on EQ-5D and VAS were 0.81 ± 0.14 and 0.73 ± 0.21, respectively. Mean self-reported smell function (on a 0-10 scale) was 9.67 ± 1.25 pre-COVID-19, 0.93 ± 2.34 at diagnosis, and 3.39 ± 2.32 at most current assessment. A total of 89.16% of the subjects reported parosmia and 24.13% sought medical care for anosmia. Seeing an MD for OD (p < 0.001), female gender (EQ-5D only, p = 0.002), a history of chronic pain (p < 0.05) and depression/anxiety (EQ-5D only, p < 0.001) predicted worse health. Parosmia and persistent symptoms, such as shortness of breath, were associated with lower EQ-5D and VAS scores, but did not independently predict poorer health scores on multivariable analysis.

CONCLUSION

Persistent COVID-19 OD results in health states comparable to other chronic diseases.

Chemosensory Dysfunction in Long-Term COVID-19 Assessed by Self-Reported and Direct Psychophysical Methods

Chemosensory dysfunction is a frequent postacute sequela of COVID-19. Depending on the type of test used to measure it (self-report vs. direct test), the degree of chemosensory dysfunction in long-term COVID-19 has been found to be highly variable. In this manuscript, we report the cross-sectional data (first assessment) of a longitudinal study (6-month follow-up) examining smell, taste, and chemesthesis in participants affected by long-term COVID-19 (COVID+) and participants without COVID-19 (COVID−) by means of both self-reported and direct psychophysical methods. In total, 208 Italian participants (COVID+ n = 133; COVID− n = 75) completed the Smell and Taste Check developed by the Global Consortium for Chemosensory Research (GCCR), which includes self-reports on smell, taste, and chemesthetic abilities as well as direct intensity ratings of unstandardized smell, taste, and chemesthetic household items. Furthermore, all participants completed SCENTinel, a validated direct smell test. We found a positive association between the self-reported, unstandardized direct test and the validated direct test for smell, indicating moderate to large agreement across measures. Furthermore, the performance on SCENTinel was significantly associated with self-reported smell loss. A positive association between the self-reports and the intensity of household items was also retrieved for taste and chemesthesis. The time relative to COVID-19 onset (267.3 ± 113.9 days) did not modulate the chemosensory performance of self-reported abilities, intensity ratings, and SCENTinel. All in all, we confirm the impairment of three chemical senses (smell, taste, and chemesthesis) in an independent sample of Italian participants affected by long-term COVID-19 by using and comparing self-reported and direct psychophysical methods. We contribute to the discussion on best practices to monitor chemosensory dysfunction in individuals affected by long-term COVID-19.

Prognosis and persistence of smell and taste dysfunction in patients with covid-19: meta-analysis with parametric cure modelling of recovery curves

OBJECTIVE

To clarify in patients with covid-19 the recovery rate of smell and taste, proportion with persistent dysfunction of smell and taste, and prognostic factors associated with recovery of smell and taste.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

PubMed, Embase, Scopus, Cochrane Library, and medRxiv from inception to 3 October 2021.

REVIEW METHODS

Two blinded reviewers selected observational studies of adults (≥18 years) with covid-19 related dysfunction of smell or taste. Descriptive prognosis studies with time-to-event curves and prognostic association studies of any prognostic factor were included.

DATA EXTRACTION AND SYNTHESIS

Two reviewers extracted data, evaluated study bias using QUIPS, and appraised evidence quality using GRADE, following PRISMA and MOOSE reporting guidelines. Using iterative numerical algorithms, time-to-event individual patient data (IPD) were reconstructed and pooled to retrieve distribution-free summary survival curves, with recovery rates reported at 30 day intervals for participants who remained alive. To estimate the proportion with persistent smell and taste dysfunction, cure fractions from Weibull non-mixture cure models of plateaued survival curves were logit transformed and pooled in a two stage meta-analysis. Conventional aggregate data meta-analysis was performed to explore unadjusted associations of prognostic factors with recovery.

MAIN OUTCOME MEASURES

The primary outcomes were the proportions of patients remaining with smell or taste dysfunction. Secondary outcomes were the odds ratios of prognostic variables associated with recovery of smell and taste.

RESULTS

18 studies (3699 patients) from 4180 records were included in reconstructed IPD meta-analyses. Risk of bias was low to moderate; conclusions remained unaltered after exclusion of four high risk studies. Evidence quality was moderate to high. Based on parametric cure modelling, persistent self-reported smell and taste dysfunction could develop in an estimated 5.6% (95% confidence interval 2.7% to 11.0%, I2=70%, τ2=0.756, 95% prediction interval 0.7% to 33.5%) and 4.4% (1.2% to 14.6%, I2=67%, τ2=0.684, 95% prediction interval 0.0% to 49.0%) of patients, respectively. Sensitivity analyses suggest these could be underestimates. At 30, 60, 90, and 180 days, respectively, 74.1% (95% confidence interval 64.0% to 81.3%), 85.8% (77.6% to 90.9%), 90.0% (83.3% to 94.0%), and 95.7% (89.5% to 98.3%) of patients recovered their sense of smell (I2=0.0-77.2%, τ2=0.006-0.050) and 78.8% (70.5% to 84.7%), 87.7% (82.0% to 91.6%), 90.3% (83.5% to 94.3%), and 98.0% (92.2% to 95.5%) recovered their sense of taste (range of I2=0.0-72.1%, τ2=0.000-0.015). Women were less likely to recover their sense of smell (odds ratio 0.52, 95% confidence interval 0.37 to 0.72, seven studies, I2=20%, τ2=0.0224) and taste (0.31, 0.13 to 0.72, seven studies, I2=78%, τ2=0.5121) than men, and patients with greater initial severity of dysfunction (0.48, 0.31 to 0.73, five studies, I2=10%, τ2<0.001) or nasal congestion (0.42, 0.18 to 0.97, three studies, I2=0%, τ2<0.001) were less likely to recover their sense of smell.

CONCLUSIONS

A substantial proportion of patients with covid-19 might develop long lasting change in their sense of smell or taste. This could contribute to the growing burden of long covid.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42021283922.

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.

Impairments in odour detection and hedonic ratings of unpleasant smells in asymptomatic university students as SARS-Cov-2 emerged locally

Sudden olfactory loss in the absence of concurrent nasal congestion is now a well-recognized symptom of COVID-19. We examined olfaction using standardized objective tests of odour detection, identification and hedonics collected from asymptomatic university students before and as SARS-CoV-2 emerged locally. Olfactory performance of students who were tested when the virus is known to be endemic (n = 22) was compared to students tested in the month prior to viral circulation (n = 25), a normative sample assessed during the previous 4 years (n = 272) and those tested in prior years during the same time period. Analyses showed significantly reduced odour detection for the virus exposed cohort compared to students tested before (t = 2.60; P = .01; d = 0.77; CI 0.17, 1.36) and to the normative sample (D = 0.38; P = .005). Odour identification scores were similar, but the exposed cohort rated odours as less unpleasant (P < .001, CLES = 0.77). Hyposmia increased 4.4-fold for students tested 2 weeks before school closure (N = 22) and increased 13.6-fold for students tested in the final week (N = 11). While the unavailability of COVID-19 testing is a limitation, this naturalistic study demonstrates week-by-week increase in hyposmia in asymptomatic students as a virus was circulating on campus, consistent with increasing airborne viral loads. The specific hedonic deficit in unpleasantness appraisal suggests a deficit in the TAAR olfactory receptor class, which conveys the social salience of odours. Assessment of odour detection and hedonic ratings may aid in early detection of SARS-CoV-2 exposure in asymptomatic and pre-symptomatic persons.

Assessment of patient recognition of coronavirus disease 2019 (COVID-19)-associated olfactory loss and recovery: a longitudinal study

Background

The clinical course of coronavirus disease 2019 (COVID‐19) olfactory dysfunction remains poorly characterized, often limited by self‐reported measures. Given the logistical challenges of psychophysical testing, understanding the longitudinal relationship between self‐reported and quantitative measures can help accurately identify patients with persistent olfactory dysfunction. This study aimed to longitudinally correlate measured and subjective olfactory function in COVID‐19 subjects.

Methods

A prospective, longitudinal study evaluating subjective and measured olfaction was conducted on ambulatory COVID‐19 subjects. Olfaction scores were obtained using a visual analogue scale (VAS) (0 = anosmia, 10 = normosmia) and the validated 12‐item Brief Smell Identification Test (BSIT). Weekly testing was performed until recovery (BSIT ≥ 9/12 and/or VAS = 10/10) or study completion.

Results

Eighty‐six polymerase chain reaction (PCR)‐positive COVID‐19 subjects were recruited ≤3 days from diagnosis and 52 completed longitudinal testing. Among those with self‐reported smell loss at recruitment, similar levels (75.8%) of objective (BSIT ≥ 9/12) and subjective recovery were obtained using a VAS cutoff ≥8, yet only 30.3% reported complete subjective recovery (VAS = 10). Median times to objective and complete subjective olfactory recovery were 12 ± 2.3 and 24 ± 3.5 days, respectively. Although both measures showed chemosensory improvement, the distributions of objective and full subjective olfactory recovery differed significantly (log rank test χ² = 6.46, degrees of freedom [df] = 1, p = 0.011). Overall correlation between BSIT and VAS scores was moderate to strong across longitudinal follow‐up (r_s = 0.41–0.65).

Conclusion

Self‐reported and psychophysically measured COVID‐19 olfactory dysfunction improve at similar levels and are moderately correlated longitudinally, yet there is a significant delay in complete subjective recovery. Psychophysical testing in conjunction with qualitative assessments may be considered for counseling and follow‐up of patients with COVID‐19 smell loss.