High prevalence of olfactory disorders 18 months after contracting COVID-19: a case-control study

Abstract

AbstractBackgroundMore 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 naïve 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.