The prevalence of sudden loss of smell in COVID-19 patients is approximately 40% to 75%. Some individuals recover from acute smell loss, only to subsequently report other olfactory dysfunctions, such as parosmia (smell distortions) and phantosmia (phantom smells or olfactory hallucinations). A longitudinal survey was conducted to characterize the smell function post-COVID-19. The smelling ability was initially measured during COVID-19 infection and then during subsequent follow-ups within 2 to 10 months after the initial survey.
During the follow-up survey, out of 1482 participants, 60% of women and 48% of men reported that their smelling ability decreased by 80% when compared to their pre-illness smell ability. Prevalence of parosmia and phantosmia was observed in 10% of participants during the initial survey. But, surprisingly during the follow-up survey, an increased number of participants, 47% and 25% complained of parosmia and phantosmia, respectively. Persistent smell impairment was associated with more symptoms overall, suggesting it may be a key marker of long-COVID. Further, olfactory dysfunctions were significantly more common in long-haulers than in non-long-haulers. 63.6% of long-haulers reported parosmia versus 23.9% of non-long-haulers. Furthermore, persistent smell loss coincided with a higher incidence of headaches.
Thus, it is concluded that parosmia and phantosmia are more prevalent among COVID-19 recovered individuals. It is important that health providers, patients, and their families are aware of this potential development, and they are educated about the course of disease and management. Millions of people worldwide are likely affected and additional research, as well as the development of new treatment options, are needed.