The Centers for Disease Control and Prevention (CDC) named “new loss of taste or smell” one of the most common symptoms of COVID-19 infection. The UC San Francisco Otolaryngology – Head and Neck Surgery team continues to research and treat olfactory loss in people infected with COVID-19 and has published three studies on this topic.
Complete (anosmia) and incomplete (hyposmia) smell sensitivity impairment are widely reported indicators among the many symptoms of COVID-19 infection. Quality of life can be substantially impacted by the loss of taste and smell, with possible effects including depression, loss of appetite, and safety risks from lack of awareness of gas leaks, smoke or spoiled food. The path to recovery of taste and smell varies widely among affected individuals.
Identifying the cause
“The loss of smell observed in COVID-19 infections is thought to be caused by direct viral injury to the chemosensory system, which is different from the mechanism seen in a typical cold or upper respiratory infection (URI),” said Lauren T. Roland, MD, head and neck surgeon at UCSF and co-author of the studies.
Smell loss due to URI occurs when nasal congestion and mucus block odorants from reaching the olfactory region of the nose located higher in the nasal cavity. “In contrast to the typical temporary loss of smell that we see with URI, many people with COVID-19 report a sudden loss of smell without associated nasal obstruction and congestion. A change in their sense of smell is sometimes their only symptom of the infection,” said Patricia Loftus, MD, rhinologist and skull base surgeon at UCSF and co-author of the studies.
“Currently, the mechanism for smell and taste loss in COVID-19 is being investigated,” Loftus added. “Histologic studies have shown that SARS-CoV-2 attacks the sustentacular cells – the cells that support the olfactory nerves in the nose. SARS-CoV-2 targets the ACE2 receptor found on the surface of sustentacular cells but not on olfactory neurons. If the supporting cells are compromised, the olfactory nerves are unable to function correctly.”
“Since taste relies on olfaction,” Loftus said, “taste loss may be present because of smell loss, but further research is needed to determine how COVID-19 affects taste receptors on the tongue and sensory nerves.”
Focusing on patient outcomes
The UCSF team maintains a focus on patient-care-related research for those with olfactory loss. “We have a lot of work underway to investigate options for improving smell in patients with loss related to COVID-19,” Roland said. “The options with the best data are nasal steroid irrigation treatments and retraining methods to help patients relearn how to detect commonly encountered scents.”
Jose G. Gurrola II, MD, rhinologist and skull base surgeon at UCSF and co-author of the studies, has acquired an advanced research olfactometer, a device for precise measurement of the sense of smell, to better understand the nature and time course of the chemosensory loss. “This device will expand our team’s ability to characterize the nature and magnitude of olfactory loss in ways that commercially available testing does not,” he said. “Most people will recover their sense of smell, although some may experience an altered sense of smell from their previous baseline. We are very interested in learning more about the recovery process, and we highly recommend that patients are evaluated as early as possible.”
Research is also key to understanding the trajectory for recovery of sense of smell or taste. “Our group followed patients with COVID-19 smell loss over time and determined the timeline to recovery based on the severity of their initial smell loss,” said Loftus. “Our studies as well as others’ work show that approximately 90 percent of patients who contract COVID-19 report a change in their sense of smell. Around 80 percent of these patients will recover their sense of smell within one to four weeks, and 95 percent will recover their smell within six months. The prognosis for the approximately 5 percent of patients who have not recovered their smell after six months is actively being studied. This knowledge has been extremely helpful in counseling patients about what they can expect in terms of their recovery.”
UCSF Medical Center has been recognized as Best in the West and No. 5 in the nation for ear, nose and throat in the 2021-2022 Best Hospitals rankings by U.S. News & World Report.
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