Loss of smell and taste has been anecdotally linked to COVID-19 infections. In a study published April 12, 2020 in the journal International Forum of Allergy & Rhinology, researchers at UC San Diego Health report the first empirical findings that strongly associate sensory loss with COVID-19, the respiratory disease caused by the novel coronavirus.
“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 Carol Yan, MD, an otolaryngologist and head and neck surgeon at UC San Diego Health.
Yan and colleagues surveyed 1,480 patients with flu-like symptoms and concerns regarding potential COVID-19 infection who underwent testing at UC San Diego Health from March 3 through March 29, 2020.
Within that total, 102 patients tested positive for the virus and 1,378 tested negative.
The study included responses from 59 COVID-19-positive patients and 203 COVID-19-negative patients.
Yan said the study demonstrated the high prevalence and unique presentation of certain sensory impairments in patients positive with COVID-19.
Of those who reported loss of smell and taste, the loss was typically profound, not mild. But encouragingly, the rate of recovery of smell and taste was high and occurred usually within two to four weeks of infection.
“Our study not only showed that the high incidence of smell and taste is specific to COVID-19 infection, but we fortunately also found that for the majority of people sensory recovery was generally rapid,” said Yan.
“Among the Covid-19 patients with smell loss, more than 70 percent had reported improvement of smell at the time of survey and of those who hadn’t reported improvement, many had only been diagnosed recently.”
Sensory return typically matched the timing of disease recovery. Interestingly, the researchers found that persons who reported experiencing a sore throat more often tested negative for COVID-19.
In an effort to decrease risk of virus transmission, UC San Diego Health now includes loss of smell and taste as a screening requirement for visitors and staff, as well as a marker for testing patients who may be positive for the virus.
Other known symptoms of COVID-19 include fever, fatigue, cough and difficulty breathing. Respondents in Yan’s study were most often persons with milder forms of COVID-19 infection who did not require hospitalization or intubation.
The findings, she said, underline the importance of identifying early or subtle symptoms of COVID-19 infection in people who may be at risk of transmitting the disease as they recuperate within the community.
“It is our hope that with these findings other institutions will follow suit and not only list smell and taste loss as a symptom of COVID-19, but use it as a screening measure for the virus across the world,” Yan said.
Co-authors include: Farhoud Faraji, Divya P. Prajapti, Christine E. Boone and Adam S. DeConde, all at UC San Diego.
Olfactory and gustatory outcomes
The occurrence of anosmia or hyposmia has been identified in the questionnaire. The impact of olfactory dysfunction on the quality of life (QoL) of patients has been assessed through the validated sQOD-NS (Appendix 1) .
This is a seven-item patient-reported outcome questionnaire including social, eating, annoyance, and anxiety questions. Each item is rated on a scale of 0–3, with higher scores reflecting better olfactory-specific QoL. The total score ranges from 0 (severe impact on QoL) to 21 (no impact on QoL) .
The rest of the olfactory and gustatory questions were based on the smell and taste component of the National Health and Nutrition Examination Survey .
This population survey was implemented by the Centers for Disease Control and Prevention to continuously monitor the health of adult citizens in the United States through a nationally representative sample of 5000 persons yearly .
The questions have been chosen to characterize the variation, timing, and associated symptoms of both olfactory and gustatory dysfunctions, and, therefore, they suggest a potential etiology. Note that we assessed the mean recovery time of olfaction through four defined propositions: 1–4 days; 5–8 days; 9–14 days; and > 15 days.
Referring to the studies that have demonstrated that the viral load was significantly decreased after 14 days , we assessed the short-term olfaction non-recovery rate on patients exhibiting double criteria: an onset of the infection > 14 days before the assessment and the lack of general symptoms at the time of the evaluation.
A total of 357 patients (85.6%) had olfactory dysfunction related to the infection. Among them, 284 (79.6%) patients were anosmic and 73 (20.4%) were hyposmic. Phantosmia and parosmia concerned 12.6% and 32.4% of patients during the disease course, respectively.
The olfactory dysfunction appeared before (11.8%), after (65.4%) or at the same time as the appearance of general or ENT symptoms (22.8%). Note that 9.4% of patients did not remember the time of onset of olfactory dysfunction and, therefore, were not considered for the percentage evaluation.
Considering the 247 patients with a clinically resolved infection (absence of general and ENT symptoms), the olfactory dysfunction persisted after the resolution of other symptoms in 63.0% of cases. The mean time between the onset of the disease and the assessment of this group of patients was 9.77 ± 5.68 days.
The short-term olfaction recovery rate, which was assessed in 59 clinically cured patients, was 44.0%. The different recovery times of the olfactory function of patients who reported a recovery of the olfactory function are available in Fig. 3.
In total, 72.6% of these patients recovered olfactory function within the first 8 days following the resolution of the disease. Among the patients who reported anosmia, then, excluding hyposmic patients, the olfactory function recovered throughout the 8 first days following the resolution of the disease in 67.8% of cases (Fig. 3).
A total of 342 patients (88.8%) reported gustatory disorders, which was characterized by impairment of the following four taste modalities: salty, sweet, bitter, and sour.
Note that 32 patients did not remember if they had gustatory dysfunction and, therefore, they were not considered for the assessment of the gustatory disorder prevalence.
The gustatory dysfunction consisted of reduced/discontinued or distorted ability to taste flavors in 78.9% and 21.1% of patients, respectively.
Among the 43 patients without gustatory dysfunction, 19 (44.2%) have no olfactory dysfunction, whereas 16 (37.2%) and 4 (9.3%) patients had anosmia or hyposmia.
The olfactory and gustatory disorders were constant and unchanged over the days in 72.8% of patients, whereas they fluctuated in 23.4% of patients. Among the patients who reported gustatory and olfactory disorders, 3.8% revealed that these disorders occurred during their rhinorrhea or nasal obstruction episodes.
Among the cured patients who had residual olfactory and/or gustatory dysfunction, 53.9% had isolated olfactory dysfunction, 22.5% had isolated gustatory dysfunction, and 23.6% had both olfactory and gustatory dysfunctions.
Olfactory and gustatory outcome associations
There was no significant association between comorbidities and the development of olfactory or gustatory dysfunctions.
Olfactory dysfunction was not significantly associated with rhinorrhea or nasal obstruction. There was a significant positive association between olfactory and gustatory dysfunctions (p < 0.001).
The statistical analysis identified a significant association between the fever and the anosmia (p = 0.014). The females would be proportionally more affected by hyposmia or anosmia compared with males (p < 0.001). Similar results were found for gustatory dysfunction (p = 0.001, Mann–Whitney U test).