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A new study based on 2,149 healthcare workers (HCWs) employed at Danderyd Hospital in Stockholm, Sweden, shows that a significant proportion of those who contracted COVID-19 experienced lasting changes to taste and smell, with 45% reporting olfactory disorders 15 months after infection, and 24% still experiencing symptoms 2.5 years after infection.
The study began in April 2020 and involved testing the HCWs for SARS-CoV-2 antibodies every 4 months. HCWs infected during the first wave of the pandemic were compared to healthy controls. All participants were asked "How has your sense of smell been during the last three days?" and to respond "always," "often," or "rarely" to the statement, "The biggest problem is not that I do not or weakly perceive odors, but that they smell different than they should," which assesses for the presence of parosmia, or altered sense of smell.
One-fourth still had loss of smell 2 years later
The authors found that 37% of the COVID-positive group suffered quantitative olfactory dysfunction, with 4 people exhibiting anosmia (loss of sense of smell), and 32 people exhibiting hyposmia, or decreased sense of smell. In the COVID-negative group, 20% showed quantitative olfactory dysfunction, all of whom had hyposmia.
Overall, first-wave infections nearly doubled the prevalence of olfactory dysfunction in the study population, from 20% to 36%, and increased the prevalence of any form of olfactory dysfunction by a full 41 percentage points compared to those without COVID.
Perhaps even more striking, 24% of all tested COVID-19 survivors still experience parosmia 2.6 years after COVID-19 diagnosis.
"Perhaps even more striking, 24% of all tested COVID-19 survivors still experience parosmia 2.6 years after COVID-19 diagnosis, nearly half of which experience medium to severe symptoms," the authors concluded. "Given the length of time, it is possible that these olfactory problems may not be fully reversible in a plurality of individuals."