RESUMO
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.
RESUMO
Reduced olfactory function is the symptom with the highest prevalence in COVID-19 with nearly 70% of individuals with COVID-19 experiencing partial or total loss of their sense of smell at some point during the disease. The exact cause is not known but beyond peripheral damage, studies have demonstrated insults to both the olfactory bulb and central olfactory brain areas. However, these studies often lack both baseline pre-COVID-19 assessments and a control group and could therefore simply reflect preexisting risk factors. Right before the COVID-19 outbreak, we completed an olfactory focused study including structural MR brain images and a full clinical olfactory test. Opportunistically, we invited participants back one year later, including 9 participants who had experienced mild to medium COVID-19 (C19+) and 12 that had not (C19-), thereby creating a pre-post controlled natural experiment with a control group. Despite C19+ participants reporting subjective olfactory dysfunction, few showed signs of objectively altered function one year later. Critically, all but one individual in the C19+ group had reduced olfactory bulb volume with an average volume reduction of 14.3%, but this did not amount to a significant between group difference compared to the control group (2.3% reduction) using inference statistics. No morphological differences in cerebral olfactory areas were found but we found stronger functional connectivity between olfactory brain areas in the C19+ croup at the post measure. Taken together, these data suggest that COVID-19 might cause a long-term reduction in olfactory bulb volume but with no discernible differences in cerebral olfactory regions.
