Young people infected with the coronavirus often slip through the net because they don't have the official symptoms of dry cough, fever and shortness of breath.
But new research has found an increasing number of young patients classified as asymptomatic share a common affliction — a loss of their sense of smell and taste, a condition known as anosmia or hyposnia (partial loss).
The data is so compelling that British experts are pushing for anosmia to be recognised as a symptom for "hidden carriers" facilitating the rapid international spread of Covid-19, the potentially deadly pneumonia caused by the coronavirus.
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Professor Nirmal Kumar, president of ENT UK — the umbrella body representing ear, nose and throat specialists — says anyone who develops anosmia should immediately self-isolate, even if they have no other signs of the disease.
"In young patients, they do not have any significant symptoms such as the cough and fever, but they may have just the loss of sense of smell and taste, which suggests that these viruses are lodging in the nose," Kumar told Sky News.
A study of international cases by the British Rhinological Society Profession and the British Association of Otorhinolaryngology found a significant proportion of coronavirus patients reported losing their sense of smell, taste or both.
In Germany, two out of every three cases had anosmia while in South Korea, where testing has been more widespread, 30 per cent of patients who tested positive reported anosmia as their major presenting symptom.
"There is already good evidence from South Korea, China and Italy that significant numbers of patients with proven Covid-19 infection have developed anosmia/hyposmia," British Rhinological Society President Claire Hopkins said in a joint statement with ENT UK.
"In addition, there have been a rapidly growing number of reports of a significant increase in the number of patients presenting with anosmia in the absence of other symptoms – this has been widely shared on medical discussion boards by surgeons from all regions managing a high incidence of cases.
"Iran has reported a sudden increase in cases of isolated anosmia, and many colleagues from the US, France and Northern Italy have the same experience.
"I have personally seen four patients this week, all under 40, and otherwise asymptomatic except for the recent onset of anosmia — I usually see roughly no more than once a month.
"I think these patients maybe some of the hitherto hidden carriers that have facilitated the rapid spread of Covid-19. Unfortunately, these patients do not meet current criteria for testing or self-isolation."
One Australian expert who agrees anosmia should be added the list of official coronavirus symptoms is Melbourne surgeon and ear, nose and throat specialist Stephen Kleid.
"One of the early symptoms [of Covid-19] that seems to be evident is significant anosmia,' he told News GP.
Kleid said the evidence was compelling enough to warrant adding anosmia to the current criteria for Covid-19 swab testing.
"Loss of sense of smell should be part of it," he said.
"If it's acute onset loss of sense of smell, then I think they should be treated as a coronavirus patient until proven otherwise.
"It will create a heightened degree of panic, but maybe we'll pick up a few more patients … and we'll know who to isolate from there."