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One year after having COVID, loss of smell remains in 1 in 3 patients

Long COVID involves significant limitations in terms of quality of life, including among young people. One of the sequelae that has the greatest impact on this population is loss of smell and taste, which is still present after one year in 1 in 3 cases.

More than a year after the start of the COVID-19 pandemic, the short-term effects of COVID-19 infection have been described in detail, but the long-term sequelae are still being studied. It has been confirmed that some complications persist even after infection, such as fatigue, muscle and joint pain, and loss of smell and taste. With the data available 6 months after the emergence of the coronavirus, it was thought that patients with persistent loss of smell and taste would account for around 10% of cases after one year.

However, more recently obtained data seems to confirm that the persistence of this symptom is actually between 25-30%. In addition, persistence is higher in women and in people under 47 years. Rates are similar in patients who were hospitalised, and those who were not.

In a study carried out by the University of Milan, 303 patients who had been infected with COVID-19 between February and May 2020 were interviewed, some of whom had required hospitalisation. 81% reported at least one symptom. The most frequent were fatigue (52%), pain (48%), and sleep disorders (47%). 36% of patients had respiratory system involvement, with dyspnoea and increased respiratory rate following light to moderate activity. Neurocognitive impairment was reported in 36% of cases, probably due to the prolonged inflammation caused by the virus, and 28% of cases involved sensory disturbances of loss of smell (hyposmia or anosmia) and loss of taste.

Some symptoms such as fatigue, muscle pain, sleep disorders, respiratory problems, cognitive impairment and difficulties with mobility were more common in those aged between 47 and 90 years. Sensory disturbances were the only symptoms with a significantly lower frequency in older people (aged 58-90 years) compared to younger adults (18-47 years). What's more, women presented a higher prevalence of all symptoms.

Some of the symptoms such as fatigue, muscle and joint pain and sleep disturbances could be caused by decreased physical activity and isolation due to the pandemic. The reason behind loss of smell and taste in SARS-CoV-2 is still unknown, and further studies are needed to explain this effect. When it comes to variants of the virus, there is emerging evidence that the delta variant does not have as great an impact on sense of smell.

The loss of smell and taste significantly affects quality of life. In terms of recovery, the only scientifically proven treatment currently available is olfactory training, which involves brief and repeated exposure to smells (once or twice a day) to stimulate the regeneration of neurons specialised in olfactory function.

Information documented by: Dr. Joaquim Mullol, head of Rhinology and the Olfaction Clinic at the Otorhinolaryngology Department at Hospital Clinic, and head of the Clinical and Experimental Respiratory Immunoallergy research group at IDIBAPS and Dr. Isam Abloid, coordinator of the Multidisciplinary Group of Skull Base Surgery at Hospital Clínic and researcher of the same research group.