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Chemosensory losses have long been considered a cardinal symptom of COVID-19 infection. Recent studies have shown changing symptom profiles with COVID-19, including decreasing incidence of olfactory losses. We accessed the National COVID Cohort Collaborative database to identify patients with and without smell and taste loss within 2 weeks of COVID-19 diagnosis. Peak prevalence time intervals for variants were determined from Covariants.org. Using rates of chemosensory loss during the peak time interval for "Untyped" variants as baseline (4/27/2020-6/18/2020), odds ratios for COVID-19-associated smell or taste disturbance fell for each of the Alpha (0.744), Delta (0.637), Omicron K (0.139), Omicron L (0.079), Omicron C (0.061), and Omicron B (0.070) peak intervals. These data suggest that during the recent Omicron waves and potentially moving forward, the presence or absence of smell and taste disturbances may no longer have predictive value in the diagnosis of COVID-19 infection., (© 2023 American Academy of Otolaryngology-Head and Neck Surgery Foundation.)

Anecdotal clinical observation suggests that rates of chemosensory dysfunction associated with COVID-19 infection may be decreasing. To investigate, the National COVID Cohort Collaborative database was queried for all patients with and without smell and taste loss within 2 weeks of COVID-19 diagnosis. Six-week periods of peak variant prevalence were selected by using CoVariants.org for analysis. Of 3,678,214 patients with COVID-19 in the database, 616,318 met inclusion criteria during the time intervals of interest, with 3431 having an associated smell or taste disturbance diagnosis. With the initial/untyped variant set as the baseline, the odds ratios for alpha, delta, and omicron (December 27, 2021-February 7, 2022) were 0.50 (95% CI, 0.45-0.55; P < .0001), 0.44 (95% CI, 0.41-0.48; P < .0001), and 0.17 (95% CI, 0.15-0.18; P < .0001), respectively. These data strongly support the clinical observation that patients infected with more recent variants are at a significantly lower risk of developing associated chemosensory loss., (© 2022 American Academy of Otolaryngology-Head and Neck Surgery Foundation.)

Since the COVID-19 pandemic began, many individuals have noted acute loss of smell and/or taste, although not all patients with these symptoms are tested for COVID-19. To better characterize all patients with these rare symptoms, a national survey was created. Over 13 days in April 2020, a total of 220 people completed the survey in its entirety, representing a wide geographic distribution across the United States. Of the 220 respondents, 93 (42%) were diagnosed with COVID-19, and 127 (58%) were not. A total of 37.7% of respondents reported changes in smell/taste as the initial or sole presentation of their condition. Most but not all patients had other symptoms suggestive of COVID-19 at the time of chemosensory loss. Despite its inclusion as a major symptom of COVID-19 by the CDC (Centers for Disease Control and Prevention), respondents with additional CDC-defined symptoms associated with COVID-19 were statistically more likely to be tested/diagnosed than those without.

Objectives: To directly measure the spatial mapping in the olfactory bulb by odor presentation and by direct electrical stimulation., Study Design: Experimental (animal)., Setting: University research laboratory., Subjects and Methods: Odor (n = 8) and electrical stimulation (n = 4) of the olfactory bulb in rats were used to demonstrate the spatial mapping of neural responses in the olfactory bulb. Both multiunit responses to odor stimulation and evoked potential responses to localized electrical stimulation were measured in different regions of the olfactory bulb., Results: Responses that were recorded simultaneously from an array of 32 electrodes positioned at different locations within the olfactory bulb were mapped. Results show different spatial patterns of neural activity for different odors (odor maps). Direct stimulation of the olfactory bulb with electrical current pulses from electrodes positioned at different locations was also effective in generating spatial patterns of neural activity., Conclusion: These data suggest that by programming an array of stimulating electrodes, it should be possible to selectively activate different regions of the olfactory bulb, generating unique patterns of neural activity as seen in normal smell., (© American Academy of Otolaryngology—Head and Neck Surgery Foundation 2016.)

The vertebrate olfactory system has become an important model for the study of neural regeneration. The most remarkable feature of this system is its unique capacity for neurogenesis and replacement of degenerating receptor neurons. This replacement is made possible by a persistent neurogenesis among basal cells. Basal cells differentiate, develop into sensory neurons and grow axon processes. Receptor cell axons project back to the olfactory bulb where they reestablish connections with the central nervous system. When mature receptors reach a critical age, are damaged by nerve injury, or are exposed to environmental agents that enter the nasal cavity, they degenerate and are subsequently replaced by newly regenerated receptor cells. Recent experiments demonstrate that olfactory neurogenesis is not simply an extension of growth and development but is a unique capacity for cell replacement that persists beyond maturity and well into old age. Even more remarkable is the finding that replacement receptor cells re-establish connections with the CNS and restore sensory function. It is expected that further studies of olfactory neurogenesis using cell and tissue culture methods will provide important advances for the field of neural regeneration.