Prevalence of olfactory and taste dysfunction in COVID-19 patients: a community care facility study

Purpose

We aim to study the prevalence of olfactory and taste dysfunction (OTD) in subjects residing in a Community Care Facility (CCF), a center unique to Singapore that is dedicated to isolate foreign workers with COVID-19 infection who have mild disease with minimal or no symptoms.

Methods

This is a cross-sectional study analyzing data prospectively collected from COVID-19-positive subjects who were admitted into a single-center Singapore EXPO CCF from 1st May 2020 to 1st July 2020. The following variables were collected: age, gender, ethnicity, anosmia, ageusia and acute respiratory infection (ARI) symptoms. Symptoms of anosmia and ageusia were self-declared via a mandatory questionnaire administered on admission.

Results

A total of 1983 subjects were included. The overall prevalence of anosmia and ageusia is 3.0% and 2.6%, respectively. 58% of anosmic subjects have co-existent ageusia and 72.6% of anosmic subjects have no concurrent sinonasal symptoms. OTD is less likely to present in subjects who are asymptomatic for ARI, compared to those symptomatic for ARI (anosmia: 2.0% versus 4.4% p = 0.002; ageusia: 1.6% versus 4.2% p < 0.001). There is a difference in the prevalence of OTD between the different ethnic groups (Indian, Chinese, Bangladeshi and Others), with Chinese and Bangladeshi reporting a higher prevalence (p < 0.043)

Conclusion

The true prevalence of OTD in COVID-19-positive subjects may be low with aggressive screening of all subjects, including those asymptomatic for ARI.

Multisensory integration supports configural learning of a home refuge in the whip spider Phrynus marginemaculatus

Whip spiders (Amblypygi) reside in structurally complex habitats and are nocturnally active yet display notable navigational abilities. From the theory that uncertainty in sensory inputs should promote multisensory representations to guide behavior, we hypothesized that their navigation is supported by a multisensory and perhaps configural representation of navigational inputs, an ability documented in a few insects and never reported in arachnids. We trained Phrynus marginemaculatus to recognize a home shelter characterized by both discriminative olfactory and tactile stimuli. In tests, subjects readily discriminated between shelters based on the paired stimuli. However, subjects failed to recognize the shelter in tests with either of the component stimuli alone. This result is consistent with the hypothesis that the terminal phase of their navigational behavior, shelter recognition, can be supported by the integration of multisensory stimuli as an enduring, configural representation. We hypothesize that multisensory learning occurs in the whip spiders' extraordinarily large mushroom bodies, which may functionally resemble the hippocampus of vertebrates.

Exploring Social Biomarkers in High-Functioning Adults with Autism and Asperger's Versus Healthy Controls: A Cross-Sectional Analysis

Biomarkers for autism spectrum disorder (ASD) are lacking but would facilitate drug development for the core deficits of the disorder. We evaluated markers proposed for characterization of differences in social communication and interaction in adults with ASD versus healthy controls (HC) for utility as biomarkers. Data pooled from an observational study and baseline data from a placebo-controlled study were analyzed. Between-group differences were observed in eye-tracking tasks for activity monitoring, biomotion, human activity preference, composite score (p = 0.0001-0.037) and pupillometry (various tasks, p = 0.017-0.05). Impaired olfaction was more common in the ASD sample versus HC (p = 0.018). Our preliminary results suggest the potential use for stratification and response sub-analyses outcome-prediction of specific eye-tracking tasks, pupillometry and olfaction tests in ASD trials.

Epidemiological, otolaryngological, olfactory and gustatory outcomes according to the severity of COVID-19: a study of 2579 patients

Objective

To investigate prevalence and epidemiological and clinical factors associated with olfactory dysfunction (OD) and gustatory dysfunction (GD) in COVID-19 patients according to the disease severity.

Study design

Cross-sectional study.

Methods

A total of 2579 patients with a positive diagnosis of COVID-19 were identified between March 22 and June 3, 2020 from 18 European hospitals. Epidemiological and clinical data were extracted. Otolaryngological symptoms, including OD and GD, were collected through patient-reported outcome questionnaire and Sniffin’Sticks tests were carried out in a subset of patients.

Results

A total of 2579 patients were included, including 2166 mild (84.0%), 144 moderate (5.6%) and 269 severe-to-critical (10.4%) patients. Mild patients presented an otolaryngological picture of the disease with OD, GD, nasal obstruction, rhinorrhea and sore throat as the most prevalent symptoms. The prevalence of subjective OD and GD was 73.7 and 46.8%, and decreases with the severity of the disease. Females had higher prevalence of subjective OD and GD compared with males. Diabetes was associated with a higher risk to develop GD. Among the subset of patients who benefited from psychophysical olfactory evaluations, there were 75 anosmic, 43 hyposmic and 113 normosmic patients. The prevalence of anosmia significantly decreased with the severity of the disease. Anosmia or hyposmia were not associated with any nasal disorder, according to SNOT-22.

Conclusion

OD and GD are more prevalent in patients with mild COVID-19 compared with individuals with moderate, severe or critical diseases. Females might have a higher risk of developing OD and GD compared with males.

Epileptic olfactory auras: a clinical spectrum

OBJECTIVE

To investigate the relative frequency of olfactory aura in a large number of patients with focal epilepsy, and examine the full clinical spectrum of epileptic olfactory auras (OAs) and their relationship to hemispheric lateralization and localization of epileptogenic focus.

METHODS

This retrospective study was based on the medical records of 1384 patients with focal epilepsy. Of these, 71 (5.1%) patients were present with OAs, comprising 25 (35.2%) men and 46 (64.8%) women with a mean age of 35.43 ± 12.89 years. These 71 patients were classified according to the clinical features of the OAs, and the electroencephalography and magnetic resonance imaging findings were examined.

RESULTS

The relative frequency of OAs was 5.1% in the focal epileptic patients. The clinical spectrum of OAs in our cases was outlined as follows, complex OAs and elementary OAs. Elementary OAs were divided into three subgroups: elementary neutral OAs, elementary unpleasant OAs, and elementary pleasant OAs. In our cases, there was no difference between the right and left hemispheres in terms of lateralization of the epileptogenic focus. In all the 71 patients, the epileptogenic zone was most commonly localized in the temporal lobe (n = 58; 81.7%).

CONCLUSIONS

The relative frequency of OAs in focal epilepsies is likely to be found higher than expected. Elementary OAs occur much more frequently than complex OAs. Among the elementary OAs, elementary unpleasant OAs and elementary neutral OAs are the most common types, whereas elementary pleasant OAs are extremely rare.

Pheromonal communication in urodelan amphibians

Pheromonal communication is an ancient and pervasive sensory modality in urodelan amphibians. One family of salamander pheromones (the sodefrin precursor-like factor (SPF) family) originated 300 million years ago, at the origin of amphibians. Although salamanders are often thought of as relatively simple animals especially when compared to mammals, the pheromonal systems are varied and complex with nuanced effects on behavior. Here, we review the function and evolution of pheromonal signals involved in male-female reproductive interactions. After describing common themes of salamander pheromonal communication, we describe what is known about the rich diversity of pheromonal communication in each salamander family. Several pheromones have been described, ranging from simple, invariant molecules to complex, variable blends of pheromones. While some pheromones elicit overt behavioral responses, others have more nuanced effects. Pheromonal signals have diversified within salamander lineages and have experienced rapid evolution. Once receptors have been matched to pheromonal ligands, rapid advance can be made to better understand the olfactory detection and processing of salamander pheromones. In particular, a large number of salamander species deliver pheromones across the skin of females, perhaps reflecting a novel mode of pheromonal communication. At the end of our review, we list some of the many intriguing unanswered questions. We hope that this review will inspire a new generation of scientists to pursue work in this rewarding field.

What's that smell? A pictorial review of the olfactory pathways and imaging assessment of the myriad pathologies that can affect them

The olfactory pathway is composed of peripheral sinonasal and central sensorineural components. The wide variety of different pathologies that can affect the olfactory pathway reflect this complex anatomical relationship. Localising olfactory pathology can present a challenge to the reporting radiologist. This imaging review will illustrate the normal anatomy of the olfactory system and describe a systematic approach to considering olfactory dysfunction. Key concepts in image interpretation will be demonstrated using examples of olfactory pathway pathologies.

Translation and validation of the short version of the Questionnaire of Olfactory Disorders-Negative Statements to Spanish

INTRODUCTION

There are more than 400 million of native Spanish speakers around the world, being the second most spoken language in regard to the number of native speakers. For this reason, a valid questionnaire to access the olfaction of our patients is necessary.

MATERIAL AND METHODS

Validation and cross-cultural adaptation of the svQOD-NS questionnaire to the Spanish language. Internal consistency of svQOD-NS measured with Cronbach α.

RESULTS

40 patients met the inclusion criteria. 41 ± 153 (range 21-82), and 32 (80%) were female. 20 patients (57,1%) were male and 15 (42,9%) were female. There was a normal distribution among patients included according to the Shapiro-Wilk test (p = 0.175). Internal consistency of svQOD-NS measured with Cronbach α was 0.861. The intraclass correlation coefficient was 0.849 (confidence interval [CI] 95%: 0.766-0.911).

CONCLUSION

The Spanish Language is the second most spoken language with regard to the number of native speakers and the svQOD-NS translation represents a valid option for the Spanish-speaking medical community, from which a large number of patients can benefit.

Road From Nose to Brain for Treatment of Alzheimer: The Bumps and Humps

Vulnerability of the brain milieu to even the subtle changes in its normal physiology is guarded by a highly efficient blood brain barrier. A number of factors i.e. molecular weight of the drug, its route of administration, lipophilic character, etc. play a significant role in its sojourn through the Blood Brain Barrier (BBB) and limit the movement of drug into brain tissue through BBB. To overcome these problems, alternative routes of drug administration have been explored to target the drugs to brain tissue. Nasal route has been widely reported for the administration of drugs for treatment of Alzheimer. In this innovative approach, the challenge of BBB is bypassed. Through this route, both the larger as well as polar molecules can be made to reach the brain tissues. Generally, these systems are either pH dependent or temperature dependent. The present review highlights the anatomy of nose, mechanisms of drug delivery from nose to brain, critical factors in the formulation of nasal drug delivery system, nasal formulations of various drugs that have been tried for their nasal delivery for treatment of Alzheimer. It also dives deep to understand the factors that contribute to the success of such formulations to carve out a direction for this niche area to be explored further.

Olfactory subsystems in the peripheral olfactory organ of anuran amphibians

Anuran amphibians (frogs and toads) typically have a complex life cycle, involving aquatic larvae that metamorphose to semi-terrestrial juveniles and adults. However, the anuran olfactory system is best known in Xenopus laevis, an animal with secondarily aquatic adults. The larval olfactory organ contains two distinct sensory epithelia: the olfactory epithelium (OE) and vomeronasal organ (VNO). The adult organ contains three: the OE, the VNO, and a "middle cavity" epithelium (MCE), each in its own chamber. The sensory epithelia of Xenopus larvae have overlapping sensory neuron morphology (ciliated or microvillus) and olfactory receptor gene expression. The MCE of adults closely resembles the OE of larvae, and senses waterborne odorants; the adult OE is distinct and senses airborne odorants. Olfactory subsystems in other (non-pipid) anurans are diverse. Many anuran larvae show a patch of olfactory epithelium exposed in the buccal cavity (bOE), associated with a grazing feeding mode. And other anuran adults do not have a sensory MCE, but many have a distinct patch of epithelium adjacent to the OE, the recessus olfactorius (RO), which senses waterborne odorants. Olfaction plays a wide variety of roles in the life of larval and adult anurans, and some progress has been made in identifying relevant odorants, including pheromones and feeding cues. Increased knowledge of the diversity of olfactory structure, of odorant receptor expression patterns, and of factors that affect the access of odorants to sensory epithelia will enable us to better understand the adaptation of the anuran olfactory system to aquatic and terrestrial environments.

Using Anti-SARS-CoV-2 IgG and IgM Antibodies to Detect Outpatient Cases with Olfactory and Taste Disorders Suspected as Mild Form of COVID-19: a Retrospective Survey

Many patients with olfactory disorders were referred during the COVID-19 pandemic in 2020. The aim of this study was to detect outpatient cases with olfactory and taste disorders suspected to mild form of COVID-19 disease in Gorgan city in the north of Iran retrospectively. This study was performed on patients who had the complaints of olfactory disorders during 03/01/2020 to 04/01/2020. They also had the mild symptoms of upper respiratory tract infection. The control group included patients who had similar symptoms during this period but did not report olfactory or taste disturbances. Due to the limitations of serologic kits, this study was performed 2-3 months after the onset of symptoms. The number of patients and controls was 72 and 36 respectively. The range and the mean ± SD of patient's age were 21-63 and 39.82 ± 9.82 years. In both groups, 44.44% were male and 55.56% were female. The time interval between the onset of symptoms and the serologic tests in both groups was 91.11 ± 16.20 days. In the cases and controls, the IgG titer was positive in 44.4% and 22.2% and the IgM titer was positive in 5.6% and 8.3% respectively. IgG antibody titers were higher in cases than in the control group (P = 0.024). There was no correlation among antibody titers and the severity of olfactory disturbances, the gender, and the age. The high COVID-19 IgG antibody titer in patients with olfactory disorder during the pandemic can probably be considered as a warning complaint of COVID-19 and may be used for isolation plans.

Protective effect of thioredoxin reductase 1 in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by the loss of dopaminergic neurons in the substantia nigra (SN). Many factors can explain the mechanism. However, the precise mechanism that contributes to the decreased number of dopaminergic neurons is unknown. Our study shows that oxidative stress is increased in models of PD compared with WT mice; Thioredoxin reductase 1(TR1) has emerged as an important antioxidant agent in dopaminergic neurons. In summary, our findings demonstrate that the overexpression of TR1 could be developed into a novel neuroprotective strategy for PD and that the reduction of the expression of GSK-3β and NF-κB could also be promising therapeutic strategies for PD. This research suggests a new direction in the treatment of PD.

Using Anti-SARS-CoV-2 IgG and IgM Antibodies to Detect Outpatient Cases with Olfactory and Taste Disorders Suspected as Mild Form of COVID-19: a Retrospective Survey

Many patients with olfactory disorders were referred during the COVID-19 pandemic in 2020. The aim of this study was to detect outpatient cases with olfactory and taste disorders suspected to mild form of COVID-19 disease in Gorgan city in the north of Iran retrospectively. This study was performed on patients who had the complaints of olfactory disorders during 03/01/2020 to 04/01/2020. They also had the mild symptoms of upper respiratory tract infection. The control group included patients who had similar symptoms during this period but did not report olfactory or taste disturbances. Due to the limitations of serologic kits, this study was performed 2–3 months after the onset of symptoms. The number of patients and controls was 72 and 36 respectively. The range and the mean ± SD of patient’s age were 21–63 and 39.82 ± 9.82 years. In both groups, 44.44% were male and 55.56% were female. The time interval between the onset of symptoms and the serologic tests in both groups was 91.11 ± 16.20 days. In the cases and controls, the IgG titer was positive in 44.4% and 22.2% and the IgM titer was positive in 5.6% and 8.3% respectively. IgG antibody titers were higher in cases than in the control group (P = 0.024). There was no correlation among antibody titers and the severity of olfactory disturbances, the gender, and the age. The high COVID-19 IgG antibody titer in patients with olfactory disorder during the pandemic can probably be considered as a warning complaint of COVID-19 and may be used for isolation plans.

Testing Olfactory and Gustatory Dysfunctions among Quarantine COVID-19 Suspects

The World Health Organization (WHO) has cautioned on specific respiratory symptoms for suspecting an individual of Corona Virus Disease 2019 (COVID-19). Meanwhile, many suspects are reporting dysfunctions of smell and taste. This study aimed to investigate the percentage of positive COVID-19 who had associated loss of sensation as detected by psychophysical testing. Eight hundred and thirty two suspects were enrolled. At the time of sampling for testing COVID-19 status, olfactory dysfunction (OD) and gustatory dysfunction (GD) tested using odorants like coffee and camphor and solutions of sweet and salty solvants, respectively. The strength of the association between test results of these sensory losses and COVID-19 positivity was assessed by calculating sensitivity, specificity, and predictive values. The responses in positive and negative individuals presented as age-adjusted odds ratio with 95% CI. Seventy six (9.1%) [95% CI: 7.4%–11.3%] of 832 suspects were tested positive for COVID-19. Paediatric cases of age between 2 and 10 years could not reply appropriately, hence OD in 134 and GD in 118 could not be tested. Anosmia or hyposmia was present in 62 (81.6%) and ageusia in 64 (84.2%) of the total 76 confirmed cases. The OD and GD dysfunctions were significantly higher among confirmed COVID-19 cases compared to negative subjects [_Adj OR (95% CI): Smell 3.22 (1.77–5.88); taste 3.05 (1.61–5.76), p < 0.001]. In this study, testing of smell and taste dysfunctions had higher sensitivity in identifying recent-onset loss of sensations in COVID-19 cases. Hence, it may be used as a simple and cost-effective screening test.

Brief Report: Odour Awareness in Young Children with Autism Spectrum Disorders

The elucidation of odour awareness in children with autism spectrum disorders (ASD) is important. We compared the odour awareness of young children with ASD with those of typical development (TD) children using the Children's Olfactory Behavior in Everyday Life (COBEL) questionnaire, which is a self-report measure that mainly assesses odour awareness. Forty-five young boys (aged 5-6 years), including 20 children with ASD and 25 TD children, participated in this study. The total COBEL score of the young children with ASD was lower than that of the TD children (p < 0.01). Moreover, the total COBEL score was significantly correlated with the total VABS II score (p < 0.05). Our results improve understanding of the odour awareness in children with ASD.

Mechanisms of cell specification and differentiation in vertebrate cranial sensory systems

Vertebrates sense a large variety of sensory stimuli that ranges from temperature, volatile and nonvolatile chemicals, touch, pain, light, sound and gravity. To achieve this, they use specialized cells present in sensory organs and cranial ganglia. Much of our understanding of the transcription factors and mechanisms responsible for sensory cell specification comes from cell-lineage tracing and genetic experiments in different species, but recent advances in single-cell transcriptomics, high-resolution imaging and systems biology approaches have allowed to study these processes in an unprecedented resolution. Here I will point to the transcription factor programs driving cell diversity in the different sensory organs of vertebrates to then discuss in vivo data of how cell specification is coupled with tissue morphogenesis.

Characterising the sensory quality and volatile aroma profile of clean-label sucrose reduced sponge cakes

The sensory and aroma quality of 30% (w/w) sucrose reduced sponge cakes incorporating clean-label replacers were investigated. The sensory quality of the reformulated sponge cakes varied, with those containing apple pomace powder (APP) showing the greatest difference to the control (SC100). Volatile profiles mainly differed in relation to compounds derived from the Maillard reaction, caramelisation and lipid oxidation. Thrity six aroma active volatile compounds were identified in the SC100, APP and oligofructose (OLIGO) sponge cakes by olfactometry. Furfural 'spicy bready' contributed most to the overall aroma of all samples, with factor dilution values differing the most for heptanal 'fatty cake crust', methional 'potato damp', and 2,5-dimethylpyrazine 'cake crust, nutty'. This study provides an in-depth insight into the impact of sugar reduction reformulation on the sensory perception of sponge cakes and demonstrates how this approach can be used to improve the sensory perception of reduced sucrose sponge cakes.

Anosmia: an evolution of our understanding of its importance in COVID-19 and what questions remain to be answered

BACKGROUND

From the start of the pandemic, many European otolaryngologists observed an unprecendented number of anosmic patients. Early reports proposed that anosmia could be the first or even the only symptom of COVID-19 infection, prompting calls for self-isolation in affected patients.

METHODS

In the present article, we review the COVID-19 anosmia literature and try to answer the following two questions: first, why is COVID-19 infection responsible for such a high incidence of anosmia? Second, in patients with more severe forms is anosmia really less prevalent and why?

RESULTS

In terms of the etiology of olfactory dysfunction, several hypotheses were proposed at the outset of the pandemic; that olfactory cleft inflammation and obstruction caused a localized conductive loss, that there was injury to the sustentacular supporting cells in the olfactory epithelium or, given the known neurotropic potential of coronavirus, that the virus could invade and damage the olfactory bulb. Olfactory cleft obstruction may contribute to the olfactory dysfunction in some patients, perhaps most likely in those that show very early resolution, it cannot account for the loss in all patients. Moreover, disordered regrowth and a predominance of immature neurons have been shown to be associated with parosmia, which is a common finding amongst patients with Covid-related anosmia. A central mechanism therefore certainly seems to be consistent with the group of patients with more prolonged olfactory deficits. Sustentacular cells showing ACE-2 immunohistochemical expression 200 to 700 times greater than nasal or tracheal epithelia seem to be the main SARS-CoV-2 gateway. As the pathophysiology of COVID-19 anosmia seems to be better understood, the question of why patients with a moderate to severe form of COVID-19 infection have less olfactory involvement remains unresolved. Different potential explanations are discussed in this review.

CONCLUSIONS

The last 5 months have benefited from great international collaborative research, first highlighting and then proving the value of loss of smell and taste as a symptom of COVID-19. Adoption of loss of smell into the case definition by international public health bodies will facilitate control of disease transmission.

COVID-19 Viral Load in the Severity of and Recovery From Olfactory and Gustatory Dysfunction

Objectives/Hypothesis

This study investigated olfactory and gustatory dysfunction in the 2020 novel coronavirus disease (COVID‐19) patients, and their correlations with viral load evaluation.

Study Design

Prospective cross‐sectional cohort study.

Methods

One hundred forty‐three symptomatic patients being screened for severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) were invited to participate. The clinical data of 83 confirmed COVID‐19 subjects were collected, with 60 patients who were symptomatic but negative for COVID‐19 recruited as controls. The prevalence and severity of and recovery time for olfactory and gustatory dysfunction, and cycle threshold (Ct) values from a SARS‐CoV‐2 polymerase chain reaction assay of nasopharyngeal and deep throat swabs were collected. Their correlations with Ct values were reported.

Results

Thirty‐nine (47.0%) and 36 (43.4%) COVID‐19 patients reported olfactory and gustatory dysfunction, respectively. The results of one‐way analysis of variance did not show statistically significant relationships between the Ct values and severity of olfactory and gustatory dysfunction (P = .780 and P = .121, respectively). Among the COVID‐19 patients who reported smell and taste loss, 28/39 (71.8%) and 30/36 (83.3%) experienced complete recovery, respectively. The mean recovery time was 10.3 ± 8.1 days for olfactory dysfunction and 9.5 ± 6.8 days for gustatory dysfunction. The recovery time was not correlated with the Ct values (Pearson correlation coefficient, smell: −0.008, P = .968; taste: −0.015, P = .940).

Conclusions

There is a high prevalence of olfactory and gustatory dysfunction in COVID‐19. However, the severity of and recovery from these symptoms have no correlations with the viral load of SARS‐CoV‐2.

Level of Evidence

4 Laryngoscope, 130:2680–2685, 2020

Postoperative malodorous smell in open septorhinoplasty: the effect of intradomal suturing with mucosal release

PURPOSE

The aim of this study was to test a mucosal release method for decreasing the occurrence of malodourous smells after septorhinoplasty by preventing formation of debris pockets after surgery.

METHODS

This study included 50 adult patients from 18 to 45 years of age who underwent open septorhinoplasty from January to May 2019. Patients were divided into two groups. The first group had intradomal (transdomal) sutures without submucosal release, while the second group had mucosal release. All patients had scheduled post-op visits at 1, 2, 4, and 8 weeks and 6 months.

RESULTS

The overall postoperative rate of malodorous smell in both mucosal release and non-mucosal release patients at 2 weeks, 8 weeks and 6 months was 43.1%, 31.4% and 5.9%, respectively. Patients 36-45 years of age had a higher rate of postoperative malodorous smell with 55.6% at 2 weeks, decreasing to 33.3% at 8 weeks, and to less than 1% at 6 months. At 2 weeks after surgery, only 20% of the mucosal release group reported a malodorous smell compared to 65.4% in the non-mucosal release group. The rate was 8% at 8 weeks, and less than 1% at 6 months in the mucosal release group compared to 53.8% at 8 weeks and 11.5% at 6 months in the non-mucosal release group.

CONCLUSIONS

Utilizing absorbable polydioxanone sutures and releasing the vestibular mucosa of the LLC significantly reduced the rate of postoperative malodorous smell for septorhinoplasty patients with intradomal (transdomal) single-dome suturing.

Computing the Effects of SARS-CoV-2 on Respiration Regulatory Mechanisms in COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been established as a cause of severe alveolar damage and pneumonia in patients with advanced Coronavirus disease (COVID-19). The consolidation of lung parenchyma precipitates the alterations in blood gases in COVID-19 patients that are known to complicate and cause hypoxemic respiratory failure. With SARS-CoV-2 damaging multiple organs in COVID-19, including the central nervous system that regulates the breathing process, it is a daunting task to compute the extent to which the failure of the central regulation of the breathing process contributes to the mortality of COVID-19 affected patients. Emerging data on COVID-19 cases from hospitals and autopsies in the last few months have helped in the understanding of the pathogenesis of respiratory failures in COVID-19. Recent reports have provided overwhelming evidence of the occurrence of acute respiratory failures in COVID-19 due to neurotropism of the brainstem by SARS-CoV-2. In this review, a cascade of events that may follow the alterations in blood gases and possible neurological damage to the respiratory regulation centers in the central nervous system (CNS) in COVID-19 are related to the basic mechanism of respiratory regulation in order to understand the acute respiratory failure reported in this disease. Though a complex metabolic and respiratory dysregulation also occurs with infections caused by SARS-CoV-1 and MERS that are known to contribute toward deaths of the patients in the past, we highlight here the role of systemic dysregulation and the CNS respiratory regulation mechanisms in the causation of mortalities seen in COVID-19. The invasion of the CNS by SARS-CoV-2, as shown recently in areas like the brainstem that control the normal breathing process with nuclei like the pre-Bötzinger complex (pre-BÖTC), may explain why some of the patients with COVID-19, who have been reported to have recovered from pneumonia, could not be weaned from invasive mechanical ventilation and the occurrences of acute respiratory arrests seen in COVID-19. This debate is important for many reasons, one of which is the fact that permanent damage to the medullary respiratory centers by SARS-CoV-2 would not benefit from mechanical ventilators, as is possibly occurring during the management of COVID-19 patients.

Do olfactory and gustatory psychophysical scores have prognostic value in COVID-19 patients? A prospective study of 106 patients

Background

The lack of objective data makes it difficult to establish the prognostic value of chemosensitive disorders in coronavirus disease 2019 (COVID-19) patients. We aimed to prospectively monitor patients diagnosed with COVID-19 to see if the severity of olfactory and gustatory dysfunction associates with subsequent disease severity.

Methods

Multicentre prospective study that recruited 106 COVID-19 subjects at diagnosis. Chemosensitive functions were assessed with psychophysical tests within 4 days of clinical onset, at 10 and 20 days. Daily body temperature and oxygen saturation were recorded as markers of disease severity alongside need for hospitalisation. The correlation between olfactory and gustatory scores and disease severity was assessed with linear regression analysis.

Results

At T0, 71 patients (67%) presented with olfactory dysfunction while gustatory impairment was detected in 76 cases (65.6%). Chemosensitive disorders gradually improved over the observation period. No significant correlations were found between T0 chemosensitive scores and final disease severity. The correlation between olfactory scores and fever proved significant at T2 (p = 0.05), while the relationship with gustatory scores was significant at T1 (p = 0.01) and T2 (p <  0.001), however neither was clinically relevant. The correlation between chemosensitive scores and oxygen saturation was significant only for taste at T2 (p <  0.001). Logistic regression analysis found significant correlations between olfactory impairment severity and need for hospitalization at T2 (OR 3.750, p = 0.005).

Conclusions

Initial objective olfactory and gustatory scores do not seem to have a significant prognostic value in predicting the severity of the COVID-19 course; however, persistence of olfactory dysfunction at 20 days, associated with a more severe course. Unfortunately, olfactory and gustatory dysfunction do not seem to hold prognostic value at the time of initial diagnosis.

Olfactory and gustatory dysfunctions as a clinical presentation of mild-to-moderate forms of the coronavirus disease (COVID-19): a multicenter European study

OBJECTIVE

To investigate the occurrence of olfactory and gustatory dysfunctions in patients with laboratory-confirmed COVID-19 infection.

METHODS

Patients with laboratory-confirmed COVID-19 infection were recruited from 12 European hospitals. The following epidemiological and clinical outcomes have been studied: age, sex, ethnicity, comorbidities, and general and otolaryngological symptoms. Patients completed olfactory and gustatory questionnaires based on the smell and taste component of the National Health and Nutrition Examination Survey, and the short version of the Questionnaire of Olfactory Disorders-Negative Statements (sQOD-NS).

RESULTS

A total of 417 mild-to-moderate COVID-19 patients completed the study (263 females). The most prevalent general symptoms consisted of cough, myalgia, and loss of appetite. Face pain and nasal obstruction were the most disease-related otolaryngological symptoms. 85.6% and 88.0% of patients reported olfactory and gustatory dysfunctions, respectively. There was a significant association between both disorders (p < 0.001). Olfactory dysfunction (OD) appeared before the other symptoms in 11.8% of cases. The sQO-NS scores were significantly lower in patients with anosmia compared with normosmic or hyposmic individuals (p = 0.001). Among the 18.2% of patients without nasal obstruction or rhinorrhea, 79.7% were hyposmic or anosmic. The early olfactory recovery rate was 44.0%. Females were significantly more affected by olfactory and gustatory dysfunctions than males (p = 0.001).

CONCLUSION

Olfactory and gustatory disorders are prevalent symptoms in European COVID-19 patients, who may not have nasal symptoms. The sudden anosmia or ageusia need to be recognized by the international scientific community as important symptoms of the COVID-19 infection.

Magnetic resonance imaging of COVID-19 anosmic patients reveals abnormalities of the olfactory bulb: Preliminary prospective study

•

COVID-19 patients with total loss of smell have more olfactory bulb abnormalities at the magnetic resonance imaging than patients without loss of smell.

•

The olfactory bulb MRI abnormalities may be objectified through a signal intensity ratio measurement that is calculated between the average signals of the olfactory bulb and the frontal white matter.

•

The loss of smell is probably due to olfactory bulb inflammation related to virus spread.

Cell type-specific patterned neural activity instructs neural map formation in the mouse olfactory system

The development of precise neural circuits is initially directed by genetic programming and subsequently refined by neural activity. In the mouse olfactory system, axons from various olfactory sensory neurons expressing the same olfactory receptor converge onto a few spatially invariant glomeruli, generating the olfactory glomerular map in the olfactory bulbs. Using the glomerular map formation as a model, this review summarizes the current understanding of mechanisms underlying topographic map development in the mouse olfactory system and highlights how neural activity instructs the map refinement process.