London, July 3: Scientists have assessed the evolution of sudden-onset altered sense of smell or taste in people with confirmed COVID-19, and have found that in nearly half of the patients the symptom may disappear within four weeks.

The researchers, including those from the Guy's and St Thomas' Hospitals in the UK, conducted a survey-based study of 202 patients -- of whom women represented 103 patients, and the average age was 56 years. COVID-19 New Symptoms Listed by CDC: Congestion or Runny Nose, Nausea and Diarrhoea, US Health Agency Adds These Three in List of Possible Coronavirus Signs.

They found that four weeks since they observed an altered sense of smell or taste, 55 patients reported complete resolution of this symptom. According to the survey-based study, published in the journal JAMA Otolaryngology - Head & Neck Surgery, 46 of the 202 patients reported an improvement in the severity within a month, and only 12 reported the symptom was unchanged or worse.

The scientists said persistent loss of smell or taste was not associated with persistent SARS-CoV-2 infection. They said smell and taste dysfunction in COVID-19 might be a consequence of nasal obstruction, or may reflect a direct effect on olfactory mucosa and the olfactory sensory neurons, subsequently leading to the symptom.

This latter mechanism, according to the researchers, is supported by the observation that most patients did not report nasal obstruction, and in those who did, the recovery of altered sense of smell or taste was independent from improvement in blocked nose.

Although alteration of the sense of smell or taste improved in most cases during the course of the disease, the researchers said these symptoms were still the most frequently reported by COVID-19 patients four weeks after testing.

Based on the findings, they said "the loss of smell or taste is among the most common and persistent symptoms of mildly symptomatic patients with COVID-19, however, most patients reported a complete resolution or improvement of these symptoms." COVID-19 Symptoms: Runny Nose, Nausea, Diarrhea Added to The List by US Health Body CDC.

According to the scientists, further follow-up studies will be needed to determine if the 10.6 per cent of patients who had not experienced any improvement, and the 40.7 per cent people with incomplete recovery will experience future improvement.