High prevalence of olfactory disorders 18 months after contracting COVID-19

BackgroundMore than a year after recovering from COVID-19, a large proportion of individuals still report olfactory dysfunctions. However, olfactory dysfunction was common also before the COVID-19 pandemic. To establish the prevalence of olfactory dysfunction while controlling for existing cases, we tested individuals with established COVID-19 in the first wave of the pandemic using psychophysical testing of smell functions. MethodsParticipants were regularly tested for SARS-CoV-2 IgG antibodies since the start of the pandemic. To assess normal rate of dysfunction in the population and skewed recruitment of individuals with prior olfactory dysfunction, SARS-CoV-2 IgG naive individuals were tested as a control group. ResultsOne and a half years after COVID-19, 37% of individuals who recovered from COVID-19 demonstrated a clinical reduction in their sense of smell, compared to only 20% of the control group. Critically, 51% of COVID-19-recovered individuals reported parosmia symptoms, compared to only 5% in the control group. ConclusionsIn summary, a full 65% of individuals who recovered from COVID-19 experienced some form of olfactory dysfunction 18 months later. This means that the first wave of COVID-19 increased the prevalence of a clinical reduction in the sense of smell in the population with 17 percentage points and the prevalence of any form of olfactory dysfunction with a staggering 41 percentage points when compared to individuals not infected by the virus. Given the amount of time since the initial insult to the olfactory system, it is likely that these olfactory problems are permanent in a plurality of patients.

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

ImportanceSudden 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. ObjectiveTo characterize smell function and recovery up to 11 months post COVID-19 infection. Settings, ParticipantsThis 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 & MeasuresPrimary 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. ResultsOn 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 RelevanceWhile 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. Trial registrationThis project was pre-registered at OSF: https://osf.io/3e6zc. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=125 SRC="FIGDIR/small/21262763v2_ufig1.gif" ALT="Figure 1"> View larger version (22K): org.highwire.dtl.DTLVardef@b2aceforg.highwire.dtl.DTLVardef@77a539org.highwire.dtl.DTLVardef@1004dbborg.highwire.dtl.DTLVardef@ef5c9c_HPS_FORMAT_FIGEXP M_FIG C_FIG Key PointsO_ST_ABSQuestionC_ST_ABSWhat are the characteristics of smell and taste recovery of COVID-19 patients? FindingsIn this preregistered observational study of 1,468 participants, smell loss is associated with a higher number of COVID-19 symptoms, and may persist for at least 11 months following disease onset. While a majority of participants report quantitative improvement in their ability to smell, the prevalence of parosmia and phantosmia increases substantially at follow-up. Taste recovers faster than smell, suggesting taste and smell recover separately and can be distinguished by the respondents. MeaningOlfactory dysfunction appears to be a component of long-COVID, with parosmia as a prominent symptom in almost half of those with smell loss. More research into treatment is needed, especially given that olfactory dysfunction is associated with depression and loss of appetite. Health professionals should be aware of these common and long lasting effects.