Sudden Loss of Taste and Smell Should Be Part of COVID-19 Screen

Alicia Ault

April 21, 2020

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

As evidence piles up documenting a sudden loss of smell and/or taste as a presenting symptom of COVID-19, the call to screen for these phenomena is growing.

A number of new publications show a high proportion of people infected with COVID-19 report loss of smell and/or taste, with their authors adding to the clamor to recognize these symptoms as potentially indicative of the infection.

In particular, there is a belief that these signs may be present in many with asymptomatic COVID-19, and therefore asking about them could be a way to prioritize people for initial testing for the SARS-CoV-2 virus in the absence of other symptoms.

Anyone testing positive could then quarantine, and their contacts could be traced.

Despite this, the World Health Organization (WHO) has not listed loss of smell or taste as potential symptoms of SARS-CoV-2 infection.

But the US Centers for Disease Control and Prevention (CDC) has now added "new loss of taste or smell" as a symptom on its COVID-19 information page.

American Academy of Otolaryngology—Head and Neck Surgery (AAO-HNS) executive vice president and CEO James C. Denneny III, MD, believes the symptoms may be an early warning signal.

And there's no downside to checking for these, Denneny told Medscape Medical News.

"Given the fact that this doesn't require any surgical procedure, biopsy, or specific treatment, I think the upside of getting it early is great," he said. "The downside of using it as a symptom, and if someone doesn't turn out to have it, is virtually zero."

Claire Hopkins, MD, president of the British Rhinological Society, and colleagues, writing in Lancet Infectious Diseases, agree.

"Physicians evaluating patients with acute-onset loss of smell or taste, particularly in the context of a patent nasal airway, should have a high index of suspicion for concomitant SARS-CoV-2 infection."

They also observe that this appears to occur, in contrast to other respiratory infections, "in the absence of nasal congestion or rhinorrhea."

Newest Publications Find Smell and Taste Loss Is Common

Author of one of the newly published studies, Carol H. Yan, MD, an otolaryngologist and head and neck surgeon at the University of California San Diego, also thinks that sudden smell and taste loss seem to be fairly specific markers of COVID-19.

In her survey of patients who presented to UC San Diego Health for SARS-CoV-2 testing, Yan and colleagues reported that 68% (40 of 59) of COVID-19-positive patients reported olfactory impairment and 71% (42 of 59) reported taste impairment.

Among the 203 people in the "control" group who were PCR-negative for SARS-CoV-2, just 16% had smell loss and 17% had taste loss, according to their results published in the International Forum of Allergy & Rhinology.

"Based on our study, if you have smell and taste loss, you are more than 10 times more likely to have COVID-19 infection than other causes of infection. The most common first sign of a COVID-19 infection remains fever, but fatigue and loss of smell and taste follow as other very common initial symptoms," said Yan.

"We know COVID-19 is an extremely contagious virus. This study supports the need to be aware of smell and taste loss as early signs of COVID-19."

Yan told Medscape Medical News that another not yet published analysis indicates that sudden loss of smell or taste "may be more representative of a mild form of disease."

Getting these people tested and isolated could therefore help prevent spread of COVID-19, she urged.

Based on Yan's report and other case reports, the UC San Diego Health system is now asking all callers to its COVID-19 hotlines, and all visitors and staff, if they've had a sudden loss of taste or smell in the last few weeks, she explained.

And Ahmad R. Sedaghat, MD, PhD, at the University of Cincinnati, Ohio, takes a similar view.

In a new systematic review of the topic published April 14 in Laryngoscope Investigative Otolaryngology, Sedaghat and colleagues write: "Anosmia (total loss of smell) without nasal obstruction, in particular, appears to be a highly specific indicator of COVID-19."

Sedaghat said a sudden loss of sense of smell wouldn't necessarily lead people to think they have COVID-19, particularly if they remain asymptomatic, so "these individuals could continue business as usual and spread the disease as a carrier."

"If someone experiences anosmia without nasal obstruction, aside from quarantining, it would not be unreasonable to reach out to one's primary care physician about getting tested," he said in a statement from his institution.

Symptom Checkers Add Weight

Several organizations around the world have begun collecting symptom reports from patients and clinicians, which has shone more light on the sudden loss of taste and smell as potential flags for COVID-19.

In an April 14 Morbidity and Mortality Weekly report from the CDC on COVID-19 infections in healthcare workers, of the 5000 who reported symptoms, 750 (16%) wrote "loss of smell or taste" as an "other" symptom.

Meanwhile, the COVID Symptom Tracker smartphone app, a joint effort by Massachusetts General Hospital, Boston, Stanford University, California, and King's College, London, UK, which as of press time, was monitoring some 2.5 million people, has had similar findings.

In a preprint publication on 400,000 people reporting one or more symptoms between March 24 and 29 on the tracker, 18% had lost their sense of smell or taste — more than the 10% who reported fever, but far less than the 53% who reported fatigue.

Only 1702 of the 400,000 had received a COVID-19 test.

Of those, 579 had tested positive and 1123 were negative.

The organizers estimated that of those who were positive, 59% reported losing smell or taste, compared with just 18% who tested negative.

"When combined with other symptoms, people with loss of smell and taste appear to be three times more likely to have contracted COVID-19 according to our data," said Tim Spector, MD, a genetic epidemiologist at King's College and the app's lead researcher, on the symptom tracker's website.

These people "should therefore self-isolate for 7 days to reduce the spread of the disease," he urged.

Anosmia Is the Initial Symptom in Many Patients With COVID-19

The AAO-HNS also began collecting data from physicians and patients on March 25 through its web-based 16-question symptom tracking tool.

It has received more than 500 reports of sudden taste or smell loss, said Denneny.

In a report on the first 237 responses, published in Otolaryngology-Head and Neck Surgery, anosmia (profound loss of smell) was found in 73% of subjects before a COVID-19 diagnosis and was the initial symptom in 27% of those subjects.

That latter determination "was the single most important finding," said Denneny, noting it shows that smell and taste loss are "a sentinel symptom."

Anosmia led to testing in only 40% of the cases.

Half of the reports came from otolaryngologists, but a large number came from other medical specialties, especially from family medicine.

Just 2% of reports came from patients in that first group, which was based on responses through April 3.

Denneny said that more reports are now coming in from patients, which he attributes to widespread media coverage about the loss of taste and smell.

It's still not entirely clear why SARS-CoV-2 might inhibit taste or smell. More common viruses like influenza and other coronaviruses can also cause smell and taste loss.

So far, it seems like the sensory recovery is faster for SARS-CoV-2 than the other viruses, which suggests a potentially different mechanism of action, said Yan. Patients she surveyed at UC San Diego recovered the senses within a few weeks to a month, compared to months or a year with the more common viruses.

Yan's study was partially supported by the National Institutes of Health. Sedaghat has reported no relevant financial relationships. The COVID Symptom Tracker is supported by Zoe Global Limited and has received grants from the Wellcome Trust, Medical Research Council/British Heart Foundation, and Biological Informative Markers for Stratification of Hypertension.

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