According to a study published in the journal Neurology , almost two-thirds of Covid-19-positive people admitted to an Italian hospital in March had lost their sense of smell and taste.

Notably, 22 per cent of the participants involved in the study said that loss of taste and smell was their first symptom of the virus.

Study author Francesco Bax of Santa Maria della Misericordia University Hospital in Udine, Italy, said: “Loss of smell and taste are common in people who have Covid-19 infections, and our study found that these symptoms often occur before other symptoms, like fever or shortness of breath.”

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He added: “Because of that, clinicians should consider a patient’s loss of smell and taste an early indication of infection, one that is monitored closely while keeping that patient isolated, and possibly quarantined, until a definitive diagnosis can be made. While many people show evidence of Covid-19 infection in the lungs, we found there could be more at play than what a person’s lungs can tell us.”

Study design

For the study, the researchers analysed 93 people with an average age of 63 who were admitted to the non-intensive Covid-19 unit of the hospital in March 2020.

The participants either tested positive for the virus with a swab test, or they showed signs of lung problems with a chest X-ray or scan. They were also interviewed about their symptoms.

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Loss of smell and taste was present in 58 people, or 63 per cent of the group. For 13 of the 58, or 22 per cent, the loss of smell and taste was their first symptom. The average duration of the loss of smell and taste was 25 to 30 days.

Researchers also looked at blood work to see if there were certain biomarkers of inflammation. They noted that people with a lost sense of smell and taste reported lower amounts of white blood cells or leukocytes, compared to coronavirus-infected patients who didn’t lose their sense of smell and taste. In particular, a specific subset of white blood cells called neutrophils was reduced. These cells also help the body fight infection.

Study limitations

“More research is needed to determine whether this decrease in white blood cells we observed can be used to help identify patients in the early stages of Covid-19 infection,” said Bax.

"For people whose first symptoms were loss of taste and smell, we found very few had nasal congestion, so we think obstruction of the nasal passages is an unlikely cause of these symptoms. However, the association between a blood cell imbalance and losing your sense of smell may help in identifying patients at risk," he further added.

A limitation of the study is that only the patients remaining in the hospital were interviewed in person, while people already discharged from the hospital were interviewed over phone.