A follow-up on quantitative and qualitative olfactory dysfunction and other symptoms in patients recovering from COVID-19 smell loss

Abstract

Background: Sudden smell loss is a specific early symptom of COVID-19, which, prior to the emergence of Omicron, had estimated prevalence of ~40% to 75%. Chemosensory impairments affect physical and mental health, and dietary behavior. Thus, it is critical to understand the rate and time course of smell recovery. The aim of this cohort study was to characterize smell function and recovery up to 11 months post COVID-19 infection. Methods: This longitudinal survey of individuals suffering COVID-19-related smell loss assessed disease symptoms and gustatory and olfactory function. Participants (n=12,313) who completed an initial survey (S1) about respiratory symptoms, chemosensory function and COVID-19 diagnosis between April and September 2020, were invited to complete a follow-up survey (S2). Between September 2020 and February 2021, 27.5% participants responded (n=3,386), with 1,468 being diagnosed with COVID-19 and suffering co-occurring smell and taste loss at the beginning of their illness. Results: At follow-up (median time since COVID-19 onset ~200 days), ~60% of women and ~48% of men reported less than 80% of their pre-illness smell ability. Taste typically recovered faster than smell, and taste loss rarely persisted if smell recovered. Prevalence of parosmia and phantosmia was ~10% of participants in S1 and increased substantially in S2: ~47% for parosmia and ~25% for phantosmia. Persistent smell impairment was associated with more symptoms overall, suggesting it may be a key marker of long-COVID illness. The ability to smell during COVID-19 was rated slightly lower by those who did not eventually recover their pre-illness ability to smell at S2. Conclusions: While smell ability improves for many individuals who lost it during acute COVID-19, the prevalence of parosmia and phantosmia increases substantially over time. Olfactory dysfunction is associated with broader persistent symptoms of COVID-19, and may last for many months following acute COVID-19. Taste loss in the absence of smell loss is rare. Persistent qualitative smell symptoms are emerging as common long-term sequelae; more research into treatment options is strongly warranted given that even conservative estimates suggest millions of individuals may experience parosmia following COVID-19. Healthcare providers worldwide need to be prepared to treat post COVID-19 secondary effects on physical and mental health.

The Greek Collaborative Long COVID Study: Non-Hospitalized and Hospitalized Patients Share Similar Symptom Patterns

“…In fact, there was no significant difference between the two groups (hospitalized vs. non-hospitalized) in the frequency of neurological complaints in our study with the notable exception of olfactory disorders. Parosmia and other smell disorders were most commonly reported in the non-hospitalized group of patients which is in accordance with previous reports showing that olfactory dysfunction appears to be a component of LongCOVID, with parosmia as a prominent symptom in almost half of those with smell loss [ 28 ]. In a recent study byPérez–González et al, extra-thoracic symptoms (39.1%), chest symptoms (27%), dyspnoea (20.6%) and fatigue (16.1%) were more common in hospitalized patients (52.3% vs. 38.2%) and in women (59.0% vs. 40.5%) [ 29 ].…”

Analysis of Prevalence and Predictive Factors of Long-Lasting Olfactory and Gustatory Dysfunction in COVID-19 Patients

“…In addition, a recall bias might also have influenced the accuracy of the responses given by the patients one year after infection. Although our results agree with previous studies that included similar numbers of patients and varying follow-up periods (from 2 to 18 months) [ 9 , 16 , 17 , 26 , 32 , 39 , 40 , 51 ], we acknowledge that these two sources of bias may have led to an overestimation of the overall prevalence and prognostic factors found in this study.…”

“…The prevalence of parosmia at the 12-month follow-up was 27.4% in our study, similar to that reported in [ 38 ], but lower than the 43.1% reported at the 6-month follow-up in [ 9 ] and the 46.8% reported 11 months after the infection [ 39 ]. Other studies with follow-up times ranging from seven to eighteen months have reported a rate of parosmia above 60% [ 15 , 46 , 47 ].…”

“…However, it should be noted that high rates of chemosensory dysfunction were still found in our study during follow-up, even after improvement of the subjective VAS scores. Although the frequency of chemosensory dysfunction reported in the follow-up varies considerably in the literature from 16.8 to 54.5% [ 17 , 26 , 33 , 38 , 39 ], a rate similar to that obtained in our study (near 50%) has been reported in several previous studies [ 9 , 26 , 32 , 37 , 39 , 40 ]. Such variability might be explained not only by the differences in the patients’ characteristics and follow-up periods but also by the inherent limitations of the subjective self-assessment of olfactory function [ 2 ].…”

“…In addition, the analysis of the effects of other nasal and systemic symptoms during the infection has led to divergent results in different studies. Whereas some authors relate these symptoms to worsened results in the recovery of smell and taste both in the short and long term [ 26 , 39 , 43 , 44 ], others have not found any such relation [ 31 , 35 , 38 ]. In our study, we have shown that suffering from fever at the baseline was independently associated with a higher odds ratio for chemosensory recovery (OR = 3.19; 95% CI: [1.28, 7.94], p = 0.0126).…”