Smell and taste dysfunction after covid-19

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.

Impact of olfactory disorders on personal safety and well-being: a cross-sectional observational study

OBJECTIVES

Investigate safety perceptions, quantify hazardous events, and analyse their manifestations in individuals with olfactory dysfunction through an online cross-sectional survey.

METHODS

An online survey, available from 25th February to 28th September 2022, captured data on demographics, olfactory disorder causes, safety concerns, and experienced hazardous events. Distributed via Fifth Sense channels, it targeted individuals with self-claimed olfactory dysfunction.

RESULTS

Of 432 responses, the majority were female (79.6%), aged 41-70, with 20.6% non-UK residents from 21 countries. Leading causes of dysfunction were Covid-19 (22%), idiopathic (20.8%), and congenital (14.4%). Safety concerns were high (85.9%), with gas, smoke, and food as major worries. Over 5 years, 32.2% faced ≥ 1 food incident, 14.8% ≥ 1 gas incident, 34.5% ≥ 1 gas scare, and 18.5% ≥ 1 work incident. Preventative measures were taken by 60.2% at home. Key limitations of this study were self-reported data and sampling bias of charity members.

CONCLUSION

This study highlights the significant impact of smell loss on personal safety and emotional well-being. There is an unmet need in mitigating safety concerns/events for individuals with olfactory dysfunction. We suggest collaborate strategies such as educating the public sector and high-risk sectors (e.g. gas companies), and introducing safety 'scratch and sniff' cards as a screening method. Regular assessment of an individual's olfactory ability, similar to routine assessments for other sensory systems (sight, hearing) may allow proactive identification of at-risk people and corrective measures to take place.

Validity and reliability of the Questionnaire of Olfactory Disorders for Italian-speaking patients with olfactory dysfunction

Objective

To translate and validate an Italian version of the Questionnaire of Olfactory Disorders (IT-QOD).

Materials and methods

This is a prospective, multicentre study that involved patients with olfactory dysfunction (OD). Both cases and controls underwent administration of the IT-QOD, Sino-Nasal Outcome Test-22 (SNOT-22) and psychophysical evaluation of orthonasal and retronasal olfactory function.

Results

The IT-QOD was administered to 96 patients and 38 controls. The Cronbach's alpha exceeded 0.90, indicating satisfactory internal consistency. The test-retest reliability was found to be high for both parosmia (rs = 0.944) and life quality (rs = 0.969). Patients with OD had significantly higher IT-QOD scores compared to healthy individuals (p < 0.001), indicating strong internal validity. The external validity was also satisfactory, as shown by the significant correlation with SNOT-22 (rs = -0.54) and the threshold, discrimination, and identification score (rs = -0.63).

Conclusions

The IT-QOD was demonstrated to be reliable and valid to assess the impact of OD on the quality of life of Italian-speaking patients.

One-year psychophysical evaluation of COVID-19-induced olfactory disorders: a prospective cohort study

BACKGROUND

Olfactory disorders are common in COVID-19. While many patients recover within weeks, a notable number of patients suffer from prolonged olfactory disorders. Much research has focused on the acute phase of olfactory disorders in COVID-19; however, there is still inconsistency regarding the prognosis. We aim to assess both objective and subjective olfactory function in patients with persisting olfactory disorders following COVID-19, 1 year after diagnosis.

METHODS

We objectively measured olfactory function in 77 patients who initially had COVID-19-induced smell disorders, 1 year after confirmed diagnosis. These patients previously underwent two objective measurements at approximately 3 and 6 months after COVID-19, in the context of the COCOS trial (COrticosteroids for COvid-19-induced loss of Smell). The main outcome measurement was TDI score (threshold-discrimination-identification) on Sniffin' Sticks Test (SST). Secondary outcomes included objective gustatory function on Taste Strip Test (TST), self-reported olfactory, gustatory and trigeminal function on a visual analogue scale (VAS) and outcomes on questionnaires about quality of life, and nasal symptoms.

RESULTS

The findings of this study show that 1 year following COVID-19, the median TDI score increased to 30.75 (IQR 27.38-33.5), regarded as normosmia. The median TDI score started at 21.25 (IQR 18.25-24.75) at baseline and increased to 27.5 (IQR 23.63-30.0) at 6 months following COVID-19. The increase of 9.5 points on the TDI score between baseline and 1 year after COVID-19 marks a clinically relevant improvement. Regarding the self-reported VAS score (1-10) on sense of smell, it increased from 1.2 (IQR 0.4-3.0) at baseline to 3.2 (IQR 1.4-6.0) at 6 months and further improved up to 6.1 (IQR 2.7-7.5) after 1 year. Objective gustatory function increased with 2 points on TST a year after diagnosis. Self-reported olfactory, gustatory, and trigeminal functions also improved over time, as did quality of life.

CONCLUSIONS

Objective and self-reported olfactory function continued to improve 1 year after COVID-19. The median TDI score of 30.75 (IQR 27.38-33.5) is regarded as normosmia, which is a favorable outcome. However, the rate of improvement on TDI score reduces over time.

Olfactory recovery following omicron variant infection: a psychophysical prospective case-control study with six-month follow up

OBJECTIVE

This study aimed to evaluate the recovery of olfactory function at six months in individuals infected with the coronavirus disease 2019 omicron variant, using psychophysical tests.

METHODS

A prospective case-control study that included severe acute respiratory syndrome coronavirus-2 patients infected in February and March 2022 was conducted. Patients underwent the Sniffin' Sticks test within 10 days of infection and again after at least 6 months. The olfactory scores were compared with those of a control group.

RESULTS

In all, 102 patients and 120 controls were enrolled in the study. At baseline, 26 patients (25.5 per cent) self-reported smell loss. The median threshold, discrimination and identification score was 33.6 (interquartile range, 12.5) for the cases and 36.5 (interquartile range, 4.38) for the controls (p < 0.001). Based on the threshold, discrimination and identification scores, 12 controls and 34 patients reported olfactory dysfunction (p < 0.001). Eighty cases underwent re-evaluation at six months; the median threshold, discrimination and identification score was 37.1 (interquartile range, 4.75) with no significant differences compared with the controls.

CONCLUSION

Six months after infection, the prevalence of olfactory dysfunction in patients did not differ significantly from the control population.

Self-Reported Neurological Symptoms Two Years After Hospital Discharge Among COVID-19 Survivors

Background

The acute stage of COVID-19 often presents with neurological manifestations.

Objective

This study aims to investigate the long-term neurological effects on survivors.

Methods

This study recruited 1,546 COVID-19 survivors from Wuhan, including 1,119 nonsevere cases and 427 severe survivors. Participants were interviewed two years after discharge to report their neurological symptoms. The neurological symptoms of COVID-19 were compared between survivors of severe and nonsevere COVID-19.

Results

Among the 1,546 COVID-19 survivors, 44.24% discovered at least one neurological symptom. The most prevalent self-reported symptom was fatigue (28.33%), memory deficit (13.26%), attention deficit (9.96%), myalgia (8.34%), dizziness (3.82%), and headache (2.52%). Severe cases had higher incidences of fatigue, myalgia, memory deficit, attention deficit than nonsevere cases. Older age, severe COVID-19, and comorbidity burden were associated with long-term neurological symptoms.

Conclusion

Neurological symptoms are common among COVID-19 survivors, especially in severe cases.

Classification of post COVID-19 condition symptoms: a longitudinal study in the Belgian population

OBJECTIVES

Since the onset of the COVID-19 pandemic, most research has focused on its acute pathophysiology, yet some people tend to experience persisting symptoms beyond the acute phase of infection, referred to as post COVID-19 condition (PCC). However, evidence on PCC is still scarce. This study aimed to assess the distribution, classification of symptoms and associated factors of PCC in adults.

DESIGN

Longitudinal online cohort study.

SETTING

National study in Belgium.

PARTICIPANTS

Participants were Belgian adults with a recent SARS-CoV-2 infection and were recruited when called up for contact tracing. A total of 3039 participants were included and completed an online questionnaire at the time of their infection and again 3 months later.

OUTCOME MEASURES

The baseline questionnaire assessed the initial health status of the participants and their status during the acute phase of the infection. The follow-up questionnaire assessed their PCC status 3 months after infection. A latent class analysis (LCA) was performed to assess whether there are different classes of individuals with a similar set of self-reported PCC symptoms.

RESULTS

Half of the participants reported PCC 3 months after infection (47%). The most frequent symptoms were fatigue (21%), headache (11%) and memory problems (10%). The LCA highlighted three different classes of PCC symptoms with different risk factors: (1) a combination of loss of smell and taste, (2) a combination of neurological symptoms and (3) other heterogeneous symptoms.

CONCLUSIONS

With the increasing number of people who underwent COVID-19, PCC has become an important but complex public health problem due to the heterogeneity of its symptoms. The classification of symptoms performed in this study can help give insight into different aetiologies of PCC and better plan care according to the symptoms and needs of those affected.

Choroid Plexus Modulates Subventricular Zone Adult Neurogenesis and Olfaction Through Secretion of Small Extracellular Vesicles

The choroid plexus (CP) in brain ventricles secrete cerebrospinal fluid (CSF) that bathes the adjacent subventricular zone (SVZ); the latter is the largest neurogenic region in adult brain harboring neural stem/progenitor cells (NSPCs) and supplies newborn neurons to the olfactory bulb (OB) for normal olfaction. We discovered the presence of a CP-SVZ regulatory (CSR) axis in which the CP, by secreting small extracellular vesicles (sEVs), regulated adult neurogenesis in the SVZ and maintained olfaction. The proposed CSR axis was supported by 1) differential neurogenesis outcomes in the OB when animals treated with intracerebroventricular (ICV) infusion of sEVs collected from the CP of normal or manganese (Mn)-poisoned mice, 2) progressively diminished SVZ adult neurogenesis in mice following CP-targeted knockdown of SMPD3 to suppress CP sEV secretion, and 3) compromised olfactory performance in these CP-SMPD3-knockdown mice. Collectively, our findings demonstrate the biological and physiological presence of this sEV-dependent CSR axis in adult brains.

HIGHLIGHTS

CP-secreted sEVs regulate adult neurogenesis in the SVZ.CP-secreted sEVs modulate newborn neurons in the OB.Suppression of sEV secretion from the CP deteriorates olfactory performance.

COVID-19 Patterns in Araraquara, Brazil: A Multimodal Analysis

The epidemiology of COVID-19 presented major shifts during the pandemic period. Factors such as the most common symptoms and severity of infection, the circulation of different variants, the preparedness of health services, and control efforts based on pharmaceutical and non-pharmaceutical interventions played important roles in the disease incidence. The constant evolution and changes require the continuous mapping and assessing of epidemiological features based on time-series forecasting. Nonetheless, it is necessary to identify the events, patterns, and actions that were potential factors that affected daily COVID-19 cases. In this work, we analyzed several databases, including information on social mobility, epidemiological reports, and mass population testing, to identify patterns of reported cases and events that may indicate changes in COVID-19 behavior in the city of Araraquara, Brazil. In our analysis, we used a mathematical approach with the fast Fourier transform (FFT) to map possible events and machine learning model approaches such as Seasonal Auto-regressive Integrated Moving Average (ARIMA) and neural networks (NNs) for data interpretation and temporal prospecting. Our results showed a root-mean-square error (RMSE) of about 5 (more precisely, a 4.55 error over 71 cases for 20 March 2021 and a 5.57 error over 106 cases for 3 June 2021). These results demonstrated that FFT is a useful tool for supporting the development of the best prevention and control measures for COVID-19.

SARS-CoV-2 Effects on Psychophysical Olfactory Scores: Prospective Study With Evaluation Before and 60-Days After Infection

The aim of this study was to prospectively evaluate the olfactory function in a series of individuals infected with SARS-CoV-2 and who had undergone psychophysical olfactory assessment prior to infection. Individuals unexposed to SARS-CoV-2 infection underwent a psychophysical evaluation of smell with the Sniffin' Sticks test. The subjects were followed prospectively and included in the study if they developed SARS-CoV-2 infection with a second test 60 days after recovery. At the 60-day follow-up of the 41 included subjects, 2 (4.9%) self-reported persistent olfactory dysfunction (OD). The differences between TDI scores before and after infection were statistically significant (37 [interquartile range (IQR), 34.25-39.25] vs 34.75 [IQR, 32.25-38]; p = .021). Analyzing the individual olfactory domains, the differences were significant for threshold (T) (9.75 [IQR, 9-11.25] vs 8.25 [IQR, 7.25-10.25]; p = .009) but not for odor discrimination (D) (p = .443) and identification (I) (p = .159). SARS-CoV-2 causes a significant reduction in the olfactory function, in particular affecting the olfactory threshold, even in subjects who do not self-report an OD.

Human Nasal Epithelium Damage as the Probable Mechanism Involved in the Development of Post-COVID-19 Parosmia

Purpose

Since the beginning of the COVID-19 pandemic, understanding the physiopathological mechanisms of its manifestations has been crucial to understand the disease and its implications. As the disease evolved, post-infection complications have arisen such as olfactory dysfunctions including parosmia in which odourants are perceived in a distorted or an unpleasant way.

Methods

In this article, we attempt to clarify these mechanisms and the role of human nasal epithelium in the development of post-COVID-19 parosmia.

Results

The mechanisms by which SARS-CoV-2 generates olfactory dysfunction have not been elucidated, and multiple theories have been proposed pointing to the sustentacular cells of the olfactory epithelium as the main probable target of the virus.

Conclusion

Establishing the main physiopathological mechanism of post-COVID-19 parosmia will set a path for further investigations and determine treatment and preventive options for patients who have been reported to be extensively affected in multiple aspects of their lives such as eating habits and mental health.

Prevalence of olfactory dysfunction in D614G, alpha, delta and omicron waves: a psychophysical case-control study

BACKGROUND

The purpose of this study was to compare the prevalence of olfactory dysfunction (OD) at different stages of the COVID-19 pandemic by evaluating subjects diagnosed with SARS-CoV-2 infection during the Omicron wave with psychophysical tests and comparing the results with those obtained from patients infected during the D614G, Alpha and Delta waves and with those of a control group.

METHODOLOGY

The study included adult patients diagnosed with SARS-CoV-2 infection. Depending on the time of diagnosis, the subjects were divided into four study groups: D614G; Alpha, Delta and Omicron variant groups. A group of uninfected individuals was used as control. All subjects underwent psychophysical evaluation of the olfactory function with the Connecticut Chemosensory Clinical Research Center olfactory test (D614G and Alpha groups) or the extended version of the Sniffin'Sticks test (Delta, Omicron and control groups).

RESULTS

372 cases (134 D614G group, 118 Alpha group, 32 in Delta group and 88 Omicron group) were recruited and evaluated within 10 days of infection, alongside 80 controls. Patients self-reported olfactory loss in 72.4% of cases in the D614G group, in 75.4% of cases in the Alpha group, in 65.6% of cases in the Delta group and in 18.1% in the Omicron group. Psychophysical evaluation revealed a prevalence of OD: 80.6%, 83.0%, 65.6% and 36.3% in the D614G, Alpha, Delta and Omicron group respectively. The differences between the D614G, Alpha and Delta groups were not statistically significant. The Omicron group demonstrated a significantly lower prevalence of OD than the other variants but still significantly higher than the controls.

CONCLUSIONS

During the Omicron wave OD was less prevalent than during the D614G, Alpha and Delta periods. One-third of patients have reduced olfactory function on psychophysical evaluation during the Omicron wave. Our results should be considered with caution as the VOC has not been determined with certainty.

Post-COVID-19 Syndrome in Outpatients and Its Association with Viral Load

INTRODUCTION

The COVID-19 pandemic is the result of the SARS-CoV-2 virus, which has caused more than 100 million infections and more than 2.5 million deaths worldwide, representing a serious public health problem. The gold method for detecting this virus is qRT-PCR, which is a semiquantitative technique where the viral load can be established through its cycle threshold (Ct). It has also been reported that COVID-19 generates long-term symptoms (post-COVID-19).

METHODS

After three months, a survey was performed on 70 COVID-19 confirmed patients; subsequently, we divided them into four groups (persistent symptoms, chemo-sensitive, cognitive issues, and changes in habit) in order to determine the correlation between viral load and post-COVID-19 symptoms.

RESULTS

Data show that fatigue, nervousness, anosmia, and diet changes are common long-term symptoms; in addition, a negative correlation was found between viral load and the number of post-COVID-19 symptoms.

CONCLUSION

COVID-19 generates long-term symptoms which can cause problems with psychological and social repercussions.

Post-Viral Olfactory Loss: What We Learned from the SARS-CoV-2 Pandemic

Viral infections have always been one of the most frequent causes of persistent olfactory dysfunctions accounting for 18% to 45% of all cases [...].

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.

Persisting Smell and Taste Disorders in Patients Who Recovered from SARS-CoV-2 Virus Infection-Data from the Polish PoLoCOV-CVD Study

In the majority of cases, patients infected with the SARS-CoV-2 virus experience a complete resolution of symptoms within six weeks of acquiring the infection, but an increasing number of patients report persistent symptoms. This study aimed to analyse the prevalence of self-reported smell and/or taste disorders (STDs) in a group of convalescent patients after infection with the SARS-CoV-2 virus and to identify risk factors for the disease. The study included 2218 COVID-19 convalescents after both inpatient and outpatient treatment. The sample group was analysed with regard to chronic diseases, place of isolation and clinical symptoms occurring during COVID-19 along with their duration. The assessment also included the most common symptoms of COVID-19 and the severity of the disease course. A total of 98 patients reported persistent smell and taste disorders up to three months after the end of isolation (67.4% of men and 32.6% of women). The mean age of the participants was 53.8 ± 13.5 years (49.19 ± 14.68 in patients with an STD vs. 54.01 ± 13.44 in patients without an STD). The patients treated for COVID-19 at home (p < 0.001) constituted almost the entire group of patients with persistent smell and taste disorders (97%). Among the patients with persistent smell and taste disorders, 57.1% suffered from at least one chronic condition (vs. 71.4% of patients without an STD). In patients with an STD, the number of symptoms per patient was higher than in the other group at 8.87 ± 3.65 (p = 0.018), while the most common clinical symptoms during the acute phase of COVID-19 were smell and taste disorders (84%) (p < 0.001), significant weakness (70%), headache (60%), cough (55%), arthralgia (51%) (p = 0.034) and back muscle pain (51%). Based on the results obtained, the following conclusions were drawn: the risk of developing persistent smell and taste disorders after COVID-19 is greater in younger people with less comorbidities and a higher number of symptoms during the acute phase of COVID-19. The risk is associated with clinical symptoms occurring during the acute phase of COVID-19, i.e., smell and taste disorders and arthralgia. In addition, this risk is higher in patients receiving outpatient treatment for COVID-19.