Background
More than a year after recovering from COVID-19, a large proportion of individuals, many of whom work in the healthcare sector, still report olfactory dysfunctions. However, olfactory dysfunctions were already common before the COVID-19 pandemic, making it necessary to take into account the existing baseline prevalence of these dysfunctions. To establish the adjusted prevalence of COVID-19-related olfactory dysfunctions, we assessed olfactory function in healthcare workers who contracted COVID-19 during the first wave of the pandemic using psychophysical testing.
Methods
Participants were tested continuously for IgG antibodies against SARS-CoV-2 since the start of the pandemic. To assess the baseline rate of olfactory dysfunction in the population and to control for the possibility of biased recruitment of individuals with prior olfactory dysfunction, consistently IgG-naive individuals against SARS-CoV-2 were tested as a control group.
Results
Fifteen months after contracting COVID-19, 37% of healthcare workers showed a quantitative reduction in their sense of smell, compared with only 20% of individuals in the control group. Fifty-one percent of individuals who recovered from COVID-19 reported qualitative symptoms, compared with only 5% in the control group. In a follow-up study 2.6 years after COVID-19 diagnosis, 24% of all individuals tested who had recovered still experienced parosmia.
Conclusions
In summary, 65% of healthcare workers experienced parosmia or hyposmia 15 months after contracting COVID-19. Compared with a control group, the prevalence of olfactory dysfunction in the population increased by 41 percentage points. Parosmia symptoms were still present two and a half years later in 24% of individuals infected with SARS-CoV-2. Given the time elapsed between infection and testing, olfactory problems may not be fully reversible in a plurality of individuals.