Transient loss and recovery of oral chemesthesis, taste and smell with COVID-19: A small case-control series

Abstract

Transient loss of smell is a common symptom of influenza and other upper respiratory infections. Loss of taste is possible but rare with these illnesses, and patient reports of 'taste loss' typically arise from a taste / flavor confusion. Thus, initial reports from COVID-19 patients of loss of taste and chemesthesis (i.e., chemical somatosensation like warming or cooling) were met with skepticism until multiple studies confirmed SARS-CoV-2 infections could disrupt these senses. Many studies have been based on self-report or on single time point assessments after acute illness was ended. Here, we describe intensive longitudinal data over 28 days from adults aged 18-45 years recruited in early 2021 (i.e., prior to the Delta and Omicron SARS-CoV-2 waves). These individuals were either COVID-19 positive or close contacts (per U.S. CDC criteria at the time of the study) in the first half of 2021. Upon enrollment, all participants were given nose clips, blinded samples of commercial jellybeans (Sour Cherry and Cinnamon), and scratch-n-sniff odor identification test cards (ScentCheckPro), which they used for daily assessments. In COVID-19 cases who enrolled on or before Day 10 of infection, Gaussian Process Regression showed two distinct measures of function - odor identification and odor intensity - declined relative to controls (exposed individuals who never developed COVID-19). Because enrollment began upon exposure, some participants became ill only after enrollment, which allowed us to capture baseline ratings, onset of loss, and recovery. Data from these four cases and four age- and sex- matched controls were plotted over 28 days to create panel plots. Variables included mean orthonasal intensity of four odors (ScentCheckPro), perceived nasal blockage, oral burn (Cinnamon jellybeans), and sourness and sweetness (Sour Cherry jellybeans). Controls exhibited stable ratings over time. By contrast, COVID-19 cases showed sharp deviations over time. Changes in odor intensity or odor identification were not explained by nasal blockage. No single pattern of taste loss or recovery was apparent, implying different taste qualities might recover at different rates. Oral burn was transiently reduced for some before recovering quickly, suggesting acute loss may be missed in datasets collected only after illness ends. Collectively, intensive daily testing shows orthonasal smell, oral chemesthesis and taste were each altered by acute SARS-CoV-2 infection. This disruption was dyssynchronous for different modalities, with variable loss and recovery rates across both modalities and individuals.

Keywords: Anosmia; Gustation; Longitudinal; Olfaction; Recovery; Trigeminal.

Figure 1:

Flow diagram summarizing selection of cases and controls for this case series. Blue boxes indicate the 30 participants included in the Gaussian Process model regression, and gray boxes indicate the 8 individuals shown in the in-depth panel plots.

Figure 2.

Individual (left) and group level (right) Gaussian Process Regression models for 15 controls (black) and 15 COVID-19 cases (red) who entered the study on or before day 10 of their infection. For cases, Day of Rating is centered on estimated day of infection. Odor identification scores (top) and odor intensity ratings (bottom) are shown as deviation scores calculated from a grand mean of controls across time. (A) Individual odor identification data in a Gaussian Process Regression model of deviation scores from 15 COVID-19 cases (red) and 15 controls (black). (B) Group level odor identification data in a Gaussian Process Regression model for COVID-19 cases (red) and controls (black). (C) Individual deviation scores for smell intensity ratings for 15 COVID-19 cases (red) and 15 controls. (D) Group level smell intensity data in a Gaussian Process Regression model for 15 COVID-19 cases (red) and 15 controls (black). In panels B and D, the solid line represents the group median, and the shaded region shows the interquartile range. Panels A and C show maximal loss roughly around day. Panel B shows some evidence of a learning effect for the OdorID task in the controls; no evidence of learning is seen for controls in the intensity task shown in panel D.

Figure 3:

OdorID scores, and intensity ratings from matched controls over time. These participants (Subjects 1, 3, 10, and 22) show generally consistent ratings across the study. To help illustrate uniformity across the observation period, solid (colored) lines were fit via LOESS regression and dotted lines (gray) were fit via linear regression. A vertical line on Day 0 highlights the start of the 28-day study. Open hexagons (1^st row) are the number correct on a ScentCheckPro card, while open diamonds (2^nd row) are the mean daily smell intensity ratings from the same card. Open circles (3^rd row) reflect ratings of perceived nasal blockage. Red symbols (rows 4, 5, and 6) reflect specific quality ratings from Sour Cherry jellybeans collected with a pinched nose. Orange triangles (row 7) indicate burn ratings from Cinnamon jellybeans collected with a pinched nose.

Figure 4:

OdorID scores and VAS ratings from four COVID-19 positive individuals. COVID-19 cases (subjects 35, 45, 62, and 63) tended to show transient alterations of smell, taste, and/or chemesthesis during the observation period. To help illustrate uniformity across the study days, solid lines were fit via LOESS regression. A vertical line at Day 0 was added to highlight the estimated day of infection. Symbols and rows match those used in Figure 3: row 1 is daily number correct, and row 2 is orthonasal intensity of four scratch-n-sniff patches from a ScentCheckPro card, row 3 is ratings of perceived nasal blockage, rows 4–6 are sour, sweet, and burn ratings for Sour Cherry jellybeans with the nose pinched, and row 7 is burn for Cinnamon jellybeans with the nose pinched.