Epidemiological studies of smell: discussion and perspectives

Evaluating the Onset, Severity, and Recovery of Changes to Smell and Taste Associated With COVID-19 Infection in a Singaporean Population (the COVOSMIA-19 Trial): Protocol for a Prospective Case-Control Study

Background

Sudden loss of smell and/or taste has been suggested to be an early marker of COVID-19 infection, with most findings based on self-reporting of sensory changes at a single time point.

Objective

To understand the onset, severity, and recovery of sensory changes associated with COVID-19 infection, this study will longitudinally track changes in chemosensory acuity among people with suspected COVID-19 infection using standardized test stimuli that are self-administered over 28 days.

Methods

In a prospective, case-controlled observational study, volunteers will be recruited when they present for COVID-19 screening by respiratory tract polymerase chain reaction test (“swab test”). The volunteers will initially complete a series of questionnaires to record their recent changes in smell and taste ability, followed by a brief standardized smell and taste test. Participants will receive a home-use smell and taste test kit to prospectively complete daily self-assessments of their smell and taste acuity at their place of residence for up to 4 weeks, with all data submitted for collection through web-based software.

Results

This study has been approved by the Domain Specific Review Board of the National Healthcare Group, Singapore, and is funded by the Biomedical Research Council Singapore COVID-19 Research Fund. Recruitment began on July 23, 2020, and will continue through to March 31, 2021. As of October 2, 2020, 69 participants had been recruited.

Conclusions

To our knowledge, this study will be the first to collect longitudinal data on changes to smell and taste sensitivity related to clinically diagnosed COVID-19 infection, confirmed by PCR swab test, in a population-based cohort. The findings will provide temporal insights on the onset, severity, and recovery of sensory changes with COVID-19 infection, the consistency of symptoms, and the frequency of full smell recovery among patients with COVID-19. This self-administered and cost-effective approach has many advantages over self-report questionnaire–based methods and provides a more objective measure of smell and taste changes associated with COVID-19 infection; this will encourage otherwise asymptomatic individuals who are potential spreaders of the virus to self-isolate and seek formal medical diagnosis if they experience a sudden change in sensory acuity. This broadened case finding can potentially help control the COVID-19 pandemic and reduce the emergence of clusters of infections.

Trial Registration

ClinicalTrials.gov NCT04492904; https://clinicaltrials.gov/ct2/show/NCT04492904.

International Registered Report Identifier (IRRID)

DERR1-10.2196/24797

The Prevalence of Olfactory and Gustatory Dysfunction in COVID-19 Patients: A Systematic Review and Meta-analysis

OBJECTIVE

To determine the pooled global prevalence of olfactory and gustatory dysfunction in patients with the 2019 novel coronavirus (COVID-19).

DATA SOURCES

Literature searches of PubMed, Embase, and Scopus were conducted on April 19, 2020, to include articles written in English that reported the prevalence of olfactory or gustatory dysfunction in COVID-19 patients.

REVIEW METHODS

Search strategies developed for each database contained keywords such as anosmia, dysgeusia, and COVID-19. Resulting articles were imported into a systematic review software and underwent screening. Data from articles that met inclusion criteria were extracted and analyzed. Meta-analysis using pooled prevalence estimates in a random-effects model were calculated.

RESULTS

Ten studies were analyzed for olfactory dysfunction (n = 1627), demonstrating 52.73% (95% CI, 29.64%-75.23%) prevalence among patients with COVID-19. Nine studies were analyzed for gustatory dysfunction (n = 1390), demonstrating 43.93% (95% CI, 20.46%-68.95%) prevalence. Subgroup analyses were conducted for studies evaluating olfactory dysfunction using nonvalidated and validated instruments and demonstrated 36.64% (95% CI, 18.31%-57.24%) and 86.60% (95% CI, 72.95%-95.95%) prevalence, respectively.

CONCLUSIONS

Olfactory and gustatory dysfunction are common symptoms in patients with COVID-19 and may represent early symptoms in the clinical course of infection. Increased awareness of this fact may encourage earlier diagnosis and treatment, as well as heighten vigilance for viral transmission. To our knowledge, this is the first meta-analysis to report on the prevalence of these symptoms in COVID-19 patients.

Sensory Functioning in Older Adults: Relevance for Food Preference

The world's population is aging and older adults represent the fastest growing segment of the consumer market. Changes in sensory, perceptual and cognitive function in this segment of the population have been described psychophysically, however, more is known about the young-old than the old-old or oldest-old. Only now are we exploring the potential for neuroimaging tools to probe the changes in central nervous system function related to taste and smell that are relevant to sensory perception, reward value, anticipation of and consumption of food stimuli. There is real potential for brain imaging to provide a greater understanding of older adults' consumer behavior.

Upper respiratory symptoms worsen over time and relate to clinical phenotype in chronic obstructive pulmonary disease

RATIONALE

How nasal symptoms in patients with chronic obstructive pulmonary disease (COPD) change over time and resolve during naturally occurring exacerbations has not been described previously.

OBJECTIVES

To evaluate the evolution and impact of upper airway symptoms in a well-defined COPD cohort when stable and at exacerbation.

METHODS

Patients in the London COPD cohort were asked about the presence of nasal symptoms (nasal discharge, sneezing, postnasal drip, blocked nose, and anosmia) over an 8-year period (2005-2013) every 3 months at routine clinic visits while in a stable state and daily during exacerbations with the use of diary cards. Data were prospectively collected, and, in a subgroup of patients, COPD Assessment Test scores and human rhinovirus identification by polymerase chain reaction were available. Patients were also defined as having infrequent or frequent exacerbations (<2 or ≥2 exacerbations/yr, respectively).

MEASUREMENTS AND MAIN RESULTS

At an aggregate of 4,368 visits, 209 patients with COPD were asked about their nasal symptoms. At 2,033 visits when the patients were stable, the odds ratio (OR) for nasal discharge increased by 1.32% per year (95% confidence interval [CI], 1.19-1.45; P < 0.001); the OR for sneezing increased by 1.16% (95% CI, 1.05-1.29; P = 0.005); the OR for postnasal drip increased by 1.18% (95% CI, 1.03-1.36; P = 0.016); and the OR for anosmia increased by 1.19% (95% CI, 1.03-1.37; P = 0.015). At visits when the patients were having exacerbations, nasal discharge was present for 7 days and blocked nose, sneezing, and postnasal drip increased for just 3 days. Anosmia did not change. Nasal discharge was more likely in patients with frequent exacerbations (OR, 1.96; 95% CI, 1.17-3.28; P = 0.011), and COPD Assessment Test scores were higher by 1.06 units (95% CI, 0.32-1.80; P = 0.005) when patients were stable and higher by 1.30 units (95% CI, 0.05-2.57; P = 0.042) during exacerbations.

CONCLUSIONS

Upper airway symptoms increase over time in patients with COPD and are related to the frequent exacerbation phenotype. These longitudinal changes may be due to increasing airway inflammation or to progression of COPD.

The Epidemiology of Olfactory Disorders

Insights into risk factors for olfactory decline are needed, because knowledge about its origin is limited. This impairment has important implications for human health. Several epidemiologic studies of olfaction provide insight into the prevalence of olfactory disorders. Here, we review the major population studies carried out on this topic to date. Our purpose is to characterize knowledge about olfactory disorders from human studies. We also describe the existing methods for measuring the sense of smell in population studies, present recent insights into the epidemiology of smell disorders, and discuss the risk factors identified to date. Synthesis of these data shows that olfactory dysfunction increases as people age and is worse in men. Further study of olfaction is warranted for gaining better information on the etiologies affecting its impairment, research that will have a large public health impact.

An algorithmic approach to the evaluation and treatment of olfactory disorders

PURPOSE OF REVIEW

To review the current evidence in diagnosing olfactory disorders and suggest an algorithmic approach to patients with relevant complaints.

RECENT FINDINGS

New literature suggests that the incidence of olfactory loss increases with age. Age-associated olfactory loss is often multifactorial and requires careful history and physical exam. Psychophysical tests have a role in screening patients at risk for Parkinson's and Alzheimer's disease, but there is lack of evidence regarding timing and patient selection. Prediction of olfactory improvement in patients with chronic rhinosinusitis (CRS) is difficult with variable results from different studies. Olfactory training is suggested to be an emerging modality in patients with postinfectious olfactory loss.

SUMMARY

There is no standard treatment for olfactory loss. Each patient must be approached individually based on the suspected cause. Patients with CRS may require medical management and surgical treatment for alleviation of their olfactory dysfunction.

Chapter 13: Olfactory disorders

Decreased sense of smell can lead to significant impairment of quality of life, including taste disturbance and loss of pleasure from eating with resulting changes in weight, and difficulty in avoiding health risks such as spoiled food or leaking natural gas. Recent epidemiological reports have shown that despite fairly low self-reported prevalence of these disorders in large population studies, when validated smell identification or threshold tests are used they reveal quite a high prevalence of hyposmia and anosmia in certain groups, especially the elderly. Several different pathophysiological processes, such as head trauma, aging, autoimmunity, and toxic exposures, can contribute to smell impairment, with distinct implications concerning prognosis and possible treatment. Otolaryngologists are most likely to see this symptom in patients with chronic rhinosinusitis, and this now appears to be caused more by the mucosal inflammation than by physical airway obstruction.

Smell perception in normal tension glaucoma patients

PURPOSE

The aim of this study was to quantify the ability to identify odors in normal tension glaucoma (NTG) patients and healthy subjects with and without a primary vascular dysregulation (PVD).

METHODS

Both self-assessment of smell perception and evaluation of odor identification by means of the 12-item odor identification test ("Sniffin' Sticks") were performed in the following groups of subjects: 1) 18 NTG patients with PVD (G+), 2) 18 NTG patients without PVD (G-), 3) 18 healthy subjects with PVD (H(+)) and 4) 18 healthy subjects without PVD (H-). The subjects self-assessment of smell perception was evaluated before the Sniffin' Sticks test by asking them to judge their ability to identify odors as either "average," "better than average," or "worse than average."

RESULTS

Subjects with a PVD (G+ and H(+)) can identify odors significantly better than those without a PVD (G- and H-; in a score scale of 1-12 the score point difference=2.64, 95% CI=1.88-3.40, p<0.001). No significant differences in odor identification was found between NTG (groups G+ and G-) and healthy subjects (groups H(+) and H-; score point difference=-0.14, 95% CI=-0.9-0.62, p=0.72).

CONCLUSIONS

Subjects with a PVD can identify odors significantly better than those without a PVD.