Claire Hopkins and Nirmal Kumar, from the professional body ENT UK at the Royal College of Surgeons, said evidence from South Korea, China, Italy and Germany suggested that anosmia and hyposmia, or reduced sense of smell, were markers of the coronavirus. In South Korea, 30 per cent of patients tested as positive with the virus had anosmia as their “major presenting symptom in otherwise mild cases”, they wrote.

“There is potential that if any adult with anosmia but no other symptoms was asked to self-isolate for seven days, in addition to the current symptom criteria used to trigger quarantine, we might be able to reduce the number of otherwise asymptomatic individuals who continue to act as vectors, not realising the need to self-isolate,” they said.

The World Health Organisation does not list loss of smell or taste as common symptoms for Covid-19, which it has said can cause fever, tiredness and a dry cough, with some also experiencing “aches and pains, nasal congestion, runny nose, sore throat or diarrhoea”. But new studies and anecdotal reports of patients’ experiences have pointed to loss of smell as an indicator of coronavirus infection.

Recovered coronavirus patients ‘may still be contagious’

Experts at the Aga Khan University in Pakistan published a study last week with the American Chemical Society that said the coronavirus could enter the brain through pathways close to the olfactory bulb, or the part of the brain that detects odours. It referenced previous studies that had shown that the severe acute respiratory syndrome (Sars) coronavirus – which spread from southern China in 2002-03 – had the ability to “cause neuronal death in mice by invading the brain via the nose close to the olfactory epithelium”, or tissue lining the naval cavity for the sense of smell.

Abdul Mannan Baig, co-author of the study, told The Scientist magazine on Tuesday that loss of smell and taste could be early warning signs of infection for the coronavirus, which also suggested that the virus could invade the central nervous system.

“It is important to screen the patients for neurological signs early and late in the course of Covid-19, as this could be life-saving in our fight against Covid-19 pandemic,” he said.

A study by neurological experts at the Huazhong University of Science and Technology in Wuhan, the initial epicentre of the outbreak in China, found in late February that for confirmed coronavirus patients experiencing symptoms related to their peripheral nervous system, 5.1 per cent reported a reduced ability to smell and 5.6 per cent said they had reduced sense of taste.

Hendrik Streeck, a German virologist at the University of Bonn, told German paper Frankfurter Allgemeine Zeitung that about two-thirds of the patients he interviewed in Germany described experiencing a loss of smell and taste that lasted for several days.