Recovery rates and long-term olfactory dysfunction following COVID-19 infection

ObjectivesOlfactory dysfunction is one of the most recognized symptoms of COVID-19, significantly impacting quality of life, particularly in cases where recovery is prolonged. This review aims to explore patterns of olfactory recovery post-COVID-19 infection, with particular focus on delayed recovery.Data SourcesPublished literature in the English language, including senior author's own work, online and social media platforms, and patients' anecdotal reports.MethodA comprehensive review of the literature was undertaken by the authors with guidance from the senior author with expertise in the field of olfaction.ResultsBased on self-report, an estimated 95% of patients recover their olfactory function within 6 months post-COVID-19 infection. However, psychophysical testing detects higher rates of persistent olfactory dysfunction. Recovery has been found to continue for at least 2 years postinfection; negative prognostic indicators include severe olfactory loss in the acute phase, female sex, and older age. Variability in quantitative and qualitative disturbance in prolonged cases likely reflects both peripheral and central pathophysiological mechanisms. Limitations of many of the reviewed studies reflect lack of psychophysical testing and baseline olfactory assessment.ConclusionsPost-COVID-19 olfactory dysfunction remains a significant health and psychosocial burden. Emerging evidence is improving awareness and knowledge among clinicians to better support patients through their olfactory rehabilitation, with hope of recovery after several months or years. Further research is needed to better understand the underlying pathogenesis of delayed recovery, identify at risk individuals earlier in the disease course, and develop therapeutic targets. It has been widely reported that smell/taste dysfunction resolves substantially by 2 weeks of COVID-19 infection. However, millions suffer with continued chemosensory dysfunction, years after initial infection and there is evidence that recovery continues for several years post-COVID-19 infection. When assessing literature regarding recovery rates, one must be mindful of the lack of baseline olfactory assessment before infection, and whether recovery was evaluated using self-reported questionnaires or psychophysical testing. Olfactory training should be considered when discussing treatment options with patients with long-term olfactory dysfunction following COVID-19. This review aids in further understanding, risk factors, pathophysiology, and disease trajectory in those affected with long-term chemosensory dysfunction post-COVID-19 infection.