The coronavirus that causes COVID-19 has been responsible for thousands of deaths worldwide, and we've learned that it can cause a wide range of health problems.
Data from countries like South Korea, where testing has been widespread, has shown just how varied the infection can be in different people. Many show no symptoms at all, others get a cough, while a smaller proportion has a serious respiratory infection that can result in death. Because it's a respiratory illness, it shares symptoms with many other common illnesses, including seasonal allergies. So how can people tell the difference? As noted last month, one symptom that has been identified in SARS-CoV-2-positive individuals that have no other problems has been the loss of smell, and it's being used more often to identify suspected cases. So if a person can't smell anything but doesn't have nasal congestion, it may indicate the presence of the virus.
"COVID-19 is not associated with the symptoms that are typically associated with a viral cold such as nasal blockage or mucus production," said Ahmad Sedaghat, an associate professor at the University of Cincinnati College of Medicine's Department of Otolaryngology-Head and Neck Surgery.
After reviewing nineteen studies describing the illness caused by the virus, Sedaghat came to the conclusion that the loss of smell, also called anosmia, of a patient, is "a highly specific indicator of COVID-19." His findings have been reported in Laryngoscope Investigative Otolaryngology.
"This distinction is also why it is fairly easy to distinguish COVID-19 from seasonal allergies. COVID-19 is associated with a fairly unique combination of nasal symptoms: a sudden loss of one's sense of smell, also known as 'anosmia,' without nasal obstruction," added Sedaghat. "The occurrence of sudden onset anosmia without nasal obstruction is highly predictive of COVID-19 and should trigger the individual to immediately self-quarantine with presumptive COVID-19."
COVID-19 is caused by a virus that incubates in the body before it causes symptoms, so it may take two to fourteen days after exposure to the virus for symptoms to appear. These symptoms include fever, cough, and shortness of breath. If breathing trouble gets so bad that a person has constant chest pain or a hard time standing up, it's time to seek medical attention, according to the Centers for Disease Control and Prevention.
Most people that get sick will recover. We still don't know how long the loss of smell persists in every person, however. It is assumed that in most people, the sense will return a few days or weeks after the infection resolves. It may take longer for some, however.
SARS-CoV-2 can spread if it's being produced in the lining of the nose. It can then be released via mucus. "Nasal virus production is at very high levels and tends to occur early in the disease process while patients are still asymptomatic or having very mild symptoms," Sedaghat said. "When someone sneezes, this mucus, which contains the virus, is aerosolized outwards. Similarly, if someone wipes their nose and then touches surfaces without washing their hands first, that could lead to [the] spread of COVID-19."
This knowledge may inform people that feel fine and have no idea they may be infected.
"A sudden loss of one's sense of smell wouldn't trigger most people to think they have COVID-19," said Sedaghat. "These individuals could continue business as usual and spread the disease as a carrier. The guidelines for when to formally test for COVID-19 remain fluid in the setting of limited tests. But 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."