Health Letter, September 2022
By Michael Carome, M.D.
According to the Centers for Disease Control and Prevention, there had been over 94 million reported COVID-19 cases and more than one million COVID-19 deaths in the U.S. through the end of August.
Since the earliest days of the pandemic, disturbances of smell and taste have been among the most common and distinctive symptoms of COVID-19. Major smell and taste disturbances seen in patients with COVID-19 include the following:
- Partial loss of smell (hyposmia)
- Partial loss of taste (hypogeusia)
- Complete loss of smell (anosmia)
- Complete loss of taste (ageusia)
- Distorted perception of smell (parosmia)
- Distorted perception of taste (parageusia)
- Smell hallucinations (phantosmia)
- Taste hallucinations (phantogeusia)
One study conducted in Europe in early 2020 found that among patients with moderate-to-severe COVID-19, 86% reported smell disturbances, and 88% reported taste disturbances. A more recent study suggested that the incidence of smell and taste disturbances in patients with COVID-19 was lower in patients infected with the more recent delta and omicron variants than in those infected with earlier variants.
For many COVID-19 patients, smell and taste disturbances have persisted for weeks to months after resolution of other acute symptoms and adversely affected their quality of life, thus contributing to the significant burden of illness seen with long COVID.
A new study published in the BMJ (formerly the British Medical Journal) on July 27, 2022, provided the most comprehensive assessment to date of the prognosis of the smell and taste disturbances that afflict adult COVID-19 patients.
The new BMJ study
For the study, an international team of researchers conducted a systematic review and analysis of data from 18 published observational studies of adults who had smell or taste disturbances related to COVID-19. The total number of patients included in the 18 studies combined was 3,699.
The researchers’ objectives were to determine for such patients the following:
- the rate of recovery of smell and taste disturbances;
- the proportion of patients who have persistent smell and taste disturbances; and
- the prognostic factors associated with recovery of smell and taste.
Recovery of smell
The researchers estimated that 74% of patients with smell disturbance had recovered their sense of smell by 30 days of follow-up, 86% by 60 days, 90% by 90 days and 96% by 180 days. The median time to recovery of smell was 15 days.
Four of the observational studies specified the degree of smell recovery. Among these studies, the proportion of patients who had partial recovery of smell ranged from 13% to 30%, and the proportion of those who had full recovery of smell ranged from 44% to 70% during follow-up.
The researchers estimated that, depending on the statistical method used, between 6% and 12% of patients with smell disturbance due to COVID-19 may develop persistent smell problems.
Recovery of taste
The researchers’ estimates showed a similar pattern of recovery in patients who had taste disturbances, with 79% of such patients recovering their sense of taste by 30 days of follow-up, 88% by 60 days, 90% by 90 days and 98% by 180 days. The median time to recovery of taste was 12 days.
Three of the observational studies reported the degree of taste recovery. Among these studies, the proportion of patients who had partial recovery of taste ranged from 8% to 30%, and the proportion of those who had full recovery of taste ranged from 50% to 89% during follow-up.
The researchers also estimated that, depending on the statistical method used, between 4% and 8% of patients with taste disturbance due to COVID-19 may develop persistent taste problems.
In a separate analysis involving a larger set of observational studies, the BMJ study researchers found that female sex was strongly associated with a decreased likelihood of recovery of smell and taste. Greater severity of smell disturbance was also associated with a lower probability of smell recovery, but not of taste recovery. Finally, nasal congestion was associated with a lower likelihood of smell recovery. Age and smoking history were not related to the likelihood of smell recovery.
Implications of the BMJ study
The good news from the BMJ study is that most patients with smell or taste disturbances due to COVID-19 recover within three to six months. The bad news is that a substantial minority have persistent disturbances of these critical senses.
The authors of an editorial commenting on the BMJ study highlighted the burden that persistent smell and taste disturbances will place on patients and the health care system, noting the following:
About 5% of people who report initial changes to their sense of smell or taste after covid-19 still report smell and taste dysfunction six months later and, given that an estimated 550 million cases of covid-19 have been reported worldwide as of July 2022, large numbers of patients will be seeking care for these disabling morbidities. Health systems should therefore be ready to provide support to these patients who often report feeling isolated when their symptoms are overlooked by clinicians…
Loss of smell and taste adversely affects quality of life by depriving those affected of several everyday pleasures and social bonds. People can also experience anorexia, food aversions, malnutrition, anxiety, and depression.
A separate BMJ commentary coauthored by many of the BMJ study researchers likewise noted the following:
The extensive disruptions to everyday life may inevitably wreak havoc on mental health, with one patient describing her smell impairment as a “devastating loss” that resulted in her developing depression, suicidal thoughts, and sleeping disorders… For some, the despair stems from the unpredictable and prolonged nature of sensory impairment…
Even as we learn to cope with living in the era of the covid-19 pandemic, we must keep in mind that covid-19 is not merely a simple cough and cold, but may have far-reaching and long-lasting consequences. Persistent smell and taste loss is only one of the many health issues in the disease spectrum of long covid, and it remains clear that more can and must be done for these patients.
With the number of patients suffering from persistent smell and taste disturbances and other chronic COVID-19–related conditions ever expanding, the federal government must invest more money and resources to further study and better manage these life-altering sequelae of COVID-19.