Losing Sense of Smell and Taste 'Strong Predictor' of a Person Being Infected With Coronavirus

People who suddenly lose their sense of smell and taste alongside other COVID-19 symptoms should self-isolate to prevent the spread of the new coronavirus, according to the authors of a preliminary study.

The paper, which has not been peer-reviewed, "suggests that loss of taste and smell is a strong predictor of having been infected by the COVID-19 virus," wrote the researchers. The researchers said these sensations should be added to the World Health Organization's (WHO) COVID-19 symptom list.

As those who suddenly lose their sense of smell and taste alongside other COVID-19 symptoms appear to be three times more likely to have caught the new coronavirus according to their data, they should self-isolate for 14 days to prevent the virus spreading, researchers said.

Principal investigator Tim Spector, professor of genetic epidemiology at Kings College London, told Newsweek 12 percent of the 1.5 million study participants reported the symptom, making it "common." He said it was more strongly associated with COVID-19 than a fever. Therefore, those who lose their ability to smell and taste but have no other COVID-19 symptoms should also self-isolate "if in doubt."

The team looked at data on 1,573,103 people in the U.K. who used an app to report whether they had COVID-19 symptoms between March 24 and March 29, involving 1,702 who reported having a COVID-19 test and had symptoms including losing their sense of smell and taste.

Of the 579 people who said they had tested positive for the disease, 59 percent lost their sense of smell and taste, compared with 18 percent of the 1,123 who tested negative but had least one symptom of COVID-19.

The bug that causes COVID-19 may interfere with smell receptors like many other respiratory viruses, the team said.

The researchers also tried to find which symptoms, other than anosmia (the loss of smell), were most strongly correlated and able to predict if a person tested positive for COVID-19. A combination of a loss of smell and taste as well as fever, persistent cough, fatigue, diarrhea, abdominal pain, and appetite loss emerged as the best indicators.

By applying that model to 410,598 people who reported COVID-19 symptoms but hadn't been tested, they estimate that 12.86 percent were likely to be infected by the virus.

However, the researchers said their work was limited as they relied on the participants issuing accurate reports, and that the tests the participants had may not have been accurate. As those who are sick or in contact with COVID-19 patients are more likely to be tested, the scientists may also have overestimated the number of potential cases, they said.

As widespread testing isn't happening in countries like the U.S. and the U.K., the authors argued: "It is therefore of utmost importance to identify the combination of symptoms that are most predictive of COVID-19 infection, in order to instruct on self-isolation and prevent the spreading of the disease."

Earlier this week, the U.S. overtook China in terms of confirmed COVID-19 cases, with New York particularly hard hit, as shown in the Statista graph below.

Coronavirus New York
Steep rise in coronavirus cases in New York. Statista

Reports have emerged from China, Italy, South Korea, France, Germany and the U.K. suggesting a "significant number" of confirmed COVID-19 patients had lost their sense of smell. There have also been reports of people only having anosmia, or an inability to smell.

Checking for a loss of smell and taste could be implemented as part of COVID-19 screenings, the authors said. "However its usefulness in a public health setting will depend on whether this symptom occurs early in the onset of symptoms or only after more severe symptoms, such as cough, high fever and shortness of breath are present," they added.

More research on COVID-19 symptoms, the order and how often they occur will shed light on this, the researchers said, as well as how long a person will lose these senses.

The study was submitted as a pre-print to the website medRxiv, meaning it hasn't been through the rigorous peer review process required to publish in scientific journals. Releasing studies this way enables scientists to prompt debate on a topic and is particularly useful during a fast-moving situation like a pandemic when it is useful to release and discuss information quickly.

Spector told Newsweek the same app has been launched in the U.S., and urged residents to sign up at covid.joinzoe.com.

"This is a global effort! Sign up and share the app!" he told Newsweek via email.

Jane Parker, associate professor in flavor chemistry at the U.K.'s University of Reading who did not work on the paper, said in a statement: "This paper shows good preliminary (non-peer-reviewed) evidence that loss of smell and taste is likely to be a symptom of COVID-19, but its role as an early warning signal has not been confirmed.

Parker said that there is no evidence to show that those who lose their sense of smell or taste can spread coronavirus, but given the severity of the pandemic the study's findings are convincing enough that those who suddenly lose these senses should self-isolate as a precaution.

She noted that "of the people with symptoms who tested negative for COVID-19, 18 percent self-reported loss of smell and taste. This is very high but these were undoubtedly suffering from other viral infections, so the smell loss is a good indicator, but there are other viruses going around which also have a similar effect on smell.

"This is important for any public health message. Whereas smell loss is a good indicator of COVID-19, and reason to self-isolate, it does not follow necessarily that you will develop, or have developed [COVID-19]—it does not mean you are 'immune.'"

Parker said the study was limited because the participants didn't report whether anosmia was acquired prior to other COVID-19 symptoms, during the illness or afterward, but as the app tracks over time that data may be released later.

Trish Greenhalgh, professor of primary care health sciences at the University of Oxford Nuffield Department of Primary Care Health Sciences who also didn't work on the study, commented in a statement: "This is an important study because it is the first to demonstrate scientifically and in a large population sample that loss of smell is a characteristic feature of COVID. The researchers also showed that loss of smell occasionally occurs in people who do not have COVID, and that not everyone with COVID loses their sense of smell.

Greenhalgh said while some may criticize the team for asking patients to report their own test results rather than obtaining the report from their doctor, "my own view is that most respondents would give an accurate report."

World Health Organization advice for avoiding spread of coronavirus disease (COVID-19)

Hygiene advice

  • Clean hands frequently with soap and water, or alcohol-based hand rub.
  • Wash hands after coughing or sneezing; when caring for the sick; before, during and after food preparation; before eating; after using the toilet; when hands are visibly dirty; and after handling animals or waste.
  • Maintain at least 1 meter (3 feet) distance from anyone who is coughing or sneezing.
  • Avoid touching your hands, nose and mouth. Do not spit in public.
  • Cover your mouth and nose with a tissue or bent elbow when coughing or sneezing. Discard the tissue immediately and clean your hands.

Medical advice

  • Avoid close contact with others if you have any symptoms.
  • Stay at home if you feel unwell, even with mild symptoms such as headache and runny nose, to avoid potential spread of the disease to medical facilities and other people.
  • If you develop serious symptoms (fever, cough, difficulty breathing) seek medical care early and contact local health authorities in advance.
  • Note any recent contact with others and travel details to provide to authorities who can trace and prevent spread of the disease.
  • Stay up to date on COVID-19 developments issued by health authorities and follow their guidance.

Mask and glove usage

  • Healthy individuals only need to wear a mask if taking care of a sick person.
  • Wear a mask if you are coughing or sneezing.
  • Masks are effective when used in combination with frequent hand cleaning.
  • Do not touch the mask while wearing it. Clean hands if you touch the mask.
  • Learn how to properly put on, remove and dispose of masks. Clean hands after disposing of the mask.
  • Do not reuse single-use masks.
  • Regularly washing bare hands is more effective against catching COVID-19 than wearing rubber gloves.
  • The COVID-19 virus can still be picked up on rubber gloves and transmitted by touching your face.