Crystal Cox/Business Insider
A man shops for groceries in New York City, March 27, 2020.
- A sudden loss of smell may be a symptom of the coronavirus, even when patients experience no other symptoms.
- A new case study found that a 40-year-old woman's primary COVID-19 symptom was a "sudden and complete" loss of smell.
- That aligns with evidence from South Korea, China, and Italy that suggests many asymptomatic patients experience a loss of smell.
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Most people who get the coronavirus exhibit a dry cough, fever, and difficulty breathing. Between 25% and 50% of infected people might not show no symptoms at all, while other coronavirus patients show less common symptoms like diarrhea or a loss of their senses of smell and taste.
A case study published Wednesday in the Journal of the American Medical Association describes a coronavirus patient in her 40s whose main COVID-19 symptom was a "sudden and complete" loss of smell. This is also known as anosmia. The woman had previously had a dry cough, but no fever.
The study authors tested the woman's ability to smell five different scents: caramel, goat cheese, fruit, manure, and a rose. She was unable to smell or identify any of them.
The research adds to a growing body of evidence that suggests individuals whose main symptom is a loss of smell could be infected with the new coronavirus, even if they lack other typical symptoms like cough or fever.
If a patient has all three symptoms - smell loss, cough, and fever - that "should alert the clinician" to suspect a coronavirus infection, the study said.
A swollen nasal cavity
An MRI and CT scan revealed why the patient in the case study was unable to detect smells.
The patient's olfactory cleft - a narrow space at the back of the nose into which air that carries scents flows - was swollen. The inflammation prevented odors in the inhaled air from reaching her olfactory epithelium, a mucous membrane inside the nose that detects smells.
Further examination showed that the woman's olfactory bulb (the berry-sized extension of the brain that sits above the nose and processes odor information) was normal and unharmed.
A man sneezes into a napkin.
The woman did not lose her sense of taste, the researchers reported, nor did she have a fever or a runny nose, which can sometimes cause loss of smell.
A symptom in 'hidden carriers' who spread the illness without becoming sick
Other research supports this finding.
Scientists at King's College London used a tracking app to collect self-reported COVID-19 symptom data from 1.5 million users between March 24 and March 29. About 60% of patients who tested positive for the coronavirus had reported losing their sense of smell and taste, the data showed. The research, which has yet to be peer-reviewed, revealed that the loss of smell and taste were stronger predictors of a COVID-19 diagnosis than self-reported fever.
Lucy Nicholson/Reuters
An assistant store manager rings up groceries from behind a plexiglass barrier in Los Angeles, California, March 31, 2020.
In South Korea, China, and Italy, about a third of patients who have tested positive for COVID-19 also reported a loss of smell, according to a statement from ear, nose, and throat experts with The British Association of Otorhinolaryngology.
"In South Korea, where testing has been more widespread, 30% of patients testing positive have had anosmia as their major presenting symptom in otherwise mild cases," they said.
The experts also reported that "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."
They added: "These patients may be some of the hitherto hidden carriers that have facilitated the rapid spread of COVID-19."
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