Increasing incidence of parosmia and phantosmia in patients recovering from COVID-19 smell loss

Abstract

Importance: Sudden smell loss is a specific early symptom of COVID-19, with an estimated prevalence of ~40% to 75%. Smell impairment affects physical and mental health, and dietary behavior. Thus, it is critical to understand the rate and time course of smell recovery. Objective: To characterize smell function and recovery up to 11 months post COVID-19 infection. Settings, Participants: 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 respiratory symptoms, chemosensory function, and COVID-19 diagnosis survey (S1) between April and September 2020 and completed 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. Main Outcomes & Measures: Primary outcomes are ratings of smell and taste function on a visual analog scale, and self-report of parosmia (smell distortions) and phantosmia (unexplained smells). Secondary outcomes include a checklist of other COVID-19 symptoms. Results: On 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. During COVID-19 illness, the ability to smell was slightly lower among those who did not recover their pre-illness ability to smell at S2. Conclusions and Relevance: While smell loss improves for many individuals who lost it due to COVID-19, the prevalence of parosmia and phantosmia increases substantially over time. Olfactory dysfunction is also associated with wider COVID-19 symptoms and may persist for many months after COVID-19 onset. 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 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.

Persisting Chemosensory Impairments in 366 Healthcare Workers Following COVID-19: An 11-Month Follow-up

“…In this cohort, prevalence of parosmia was at 17% at 5 months after the infection and rose to over 50% at 11 months 20 . This is in line with a recent study that reported increasing incidence of parosmia in individuals recovering from long-haul COVID-19 17 . This finding is particularly important, as parosmia has been associated with a better olfactory outcome following olfactory training, but if unresolved, it may be a much greater source of distress than isolated hyposmia 28,29 .…”

“…This study could not establish a prevalence of trigeminal dysfunction due to their testing methods. Moreover, prevalence of parosmia increases with time in COVID-19 patients, which is in line with the theory that qualitative dysfunctions following viral infection could result from faulty regeneration of olfactory sensory neurons [17][18][19] . Although many patients with long-haul COVID-19 have persistent OD, very few studies describe the prognosis for such individuals past 6-months after symptom onset.…”

The Effects of Persistent Olfactory and Gustatory Dysfunctions on Quality of Life in Long-COVID-19 Patients

“…Users with CD reported a broad spectrum of circumstances that reduced their wellbeing, such as work or study difficulties, impaired eating with loss of appetite and weight changes, social and interpersonal limitations. Additionally, Ohla and colleagues [27] in their pre-print suggest that POD in the acute phase of the disease is associated with more COVID-19 symptoms overall and may represent a key marker of long-COVID- 19.…”

Post-COVID-19 Vaccine Parosmia: A Case Report

“…Many studies discuss the long-term complication of COVID-19. The study of Ohla et al included 1468 out of 12,313 patients who reported a loss of smell and taste after the infection and full recovery of their sense of smell [13]. In the UK, as listed in the COVID-19 Oxford University/AstraZeneca Vaccine Analysis Print, 402 out of 842,270 cases are suspected of having parosmia after receiving the vaccine [14].…”