A longitudinal study of olfactory dysfunction and parosmia in mild COVID-19 cases

COVID-19-related olfactory dysfunction (OD) can persist long after patients recover from acute infection, yet few studies have investigated the long-term progression of this complication. Moreover, existing studies are focused on hyposmia/anosmia but parosmia is becoming an increasingly recognized long-term symptom.

We completed a longitudinal study about OD in individuals with mild cases of COVID-19. Participants completed a questionnaire and Brief Smell Identification Test (BSIT) one week, one month and one year after diagnosis. At one-year, participants completed an additional survey about parosmia.

We obtained questionnaires and psychophysical olfactory testing information from participants at one week (n=45), one month (n=38), and one year (n=33) post COVID-19 diagnosis. At one-year, 15.2% of participants had persistent OD and 66.7% of participants reported experiencing parosmia at some point following COVID-19 diagnosis. The mean onset of parosmia was 1.3 weeks (SD: 1.9 weeks) after diagnosis, although two patients reported delayed onset (>4 weeks after diagnosis). Eight patients (24.2%) reported ongoing parosmia one year after diagnosis. Of the patients whose parosmia resolved, the mean duration of symptoms was 7.2 weeks (SD: 7.3 weeks).

Decreased sense of smell associated with COVID-19 infection has received significant recognition in both the media and in the medical literature. Symptoms of OD and parosmia were common in our patients with COVID-19. Hyposmia, anosmia, and parosmia, all decrease quality of life, necessitating continued research to understand the pathogenesis, course of symptoms, and possible treatment for these complications.