One of the major complications of COVID-19, the disease caused by the SARS-CoV-2 pathogen, is that many who transmit the illness will show mild or no symptoms, making it very difficult to identify how many people are infected with the disease and who is therefore likely to pass it on to others. Medical professionals in countries hit by the virus are reporting a telling symptom often present in even asymptomatic carriers is a sudden loss of smell, and in some cases, taste.

Anosmia is the complete or partial loss of smell. Common illnesses such as rhinovirus, the common cold, can cause temporary anosmia as the illness irritates the nasal lining. There are some more serious conditions that can cause permanent anosmia, but it’s more commonly linked to minor illnesses with a short duration.

Medical experts across the globe have reported that a sudden loss of sense of smell could be a tell-tale sign in otherwise asymptomatic COVID-19 carriers. Ear, nose, and throat (ENT) surgeons say the virus is capable of causing swelling in the olfactory mucosa in a way not commonly seen in other viruses, and therefore the loss of sense of smell could be used as a key clinical indicator in otherwise healthy carriers of COVID-19.

The American Academy of Otolaryngology posted on its website this week that the amount of anecdotal evidence of anosmia, hyposmia (reduced ability to smell), and dysgeusia (reduced sense of taste) is significant enough that they are added to the list of screening tools for possible infection.

ENT surgeons in the UK also issued a statement urging that anosmia should be categorized as an important symptom that may indicate infection in an otherwise asymptomatic carrier, allowing clinicians at COVID-19 clinics to quickly rule out or confirm this subtle symptom.

These "silent carriers" play a key role in the catastrophic spread of the disease, as without the obvious symptoms of a fever and a persistent cough they’re able to go undetected by current screening measures.

“While further research is required, loss of smell, or anosmia, has been reported in as many as 1 in 3 patients in South Korea and, in Germany, this figure was as high as 2 in patients,” said Professor Simon Carney of Otolaryngology (head and neck surgery) at Flinders University in a statement. 

It’s recommended that patients consider calling their doctor or local health services with this early symptom as a precursor for possible treatment, though it may not require any treatment beyond self-isolating until the infection has passed. Those who experience sudden onset anosmia are encouraged to self-isolate as it would well indicate transmission of the disease.

While most commonly a temporary symptom, anosmia can have a significant effect on the sufferer’s quality of life as it’s often accompanied by the loss of sense of taste. Losing your sense of smell and taste can make eating quite an unpleasant sensation (if you think about it, some foods have pretty bizarre textures) meaning some lose their appetite, leading to malnutrition. It can also have a big impact on your state of mind as, let’s face it, being confined to your sofa can be quite depressing if you can’t even make the most of quarantine snacks.