O R I G I N A L A R T I C L E
Smell dysfunction: a biomarker for COVID-19 Shima T. Moein, MD, PhD1, Seyed MohammadReza Hashemian, MD, FCCM2, Babak Mansourafshar, MD2,
Ali Khorram-Tousi, MD1, Payam Tabarsi, MD3 and Richard L. Doty, PhD, FAAN4
Background: Severe acute respiratory syndrome- coronavirus-2 (SARS-CoV-2), the virus that causes coro- navirus disease 2019 (COVID-19), is responsible for the largest pandemic since the 1918 influenza A virus subtype H1N1 influenza outbreak. The symptoms presently recog- nized by the World Health Organization are cough, fever, tiredness, and difficulty breathing. Patient-reported smell and taste loss has been associated with COVID-19 infection, yet no empirical olfactory testing on a cohort of COVID-19 patients has been performed.
Methods: The University of Pennsylvania Smell Identifica- tion Test (UPSIT), a well-validated 40-odorant test, was ad- ministered to 60 confirmed COVID-19 inpatients and 60 age- and sex-matched controls to assess the magnitude and frequency of their olfactory dysfunction. A mixed effects analysis of variance determined whether meaningful differ- ences in test scores existed between the 2 groups and if the test scores were differentially influenced by sex.
Results: Fi�y-nine (98%) of the 60 patients exhibited some smell dysfunction (mean [95% CI] UPSIT score: 20.98 [19.47, 22.48]; controls: 34.10 [33.31, 34.88]; p < 0.0001). Thirty-
five of the 60 patients (58%) were either anosmic (15/60; 25%) or severely microsmic (20/60; 33%); 16 exhibited mod- erate microsmia (16/60; 27%), 8 mild microsmia (8/60; 13%), and 1 normosmia (1/60; 2%). Deficits were evident for all 40 UPSIT odorants. No meaningful relationships between the test scores and sex, disease severity, or comorbidities were found.
Conclusion: Quantitative smell testing demonstrates that decreased smell function, but not always anosmia, is a major marker for SARS-CoV-2 infection and suggests the possibility that smell testing may help, in some cases, to identify COVID-19 patients in need of early treatment or quarantine. C© 2020 ARS-AAOA, LLC.
Key Words: chronic rhinosinusitis; olfactory disorders; olfaction; olfac- tory test; UPSIT; COVID-19; biomarker
How to Cite this Article: Moein ST, Hashemian SM, Mansourafshar B, Khorram- Tousi A, Tabarsi P, Doty RL. Smell dysfunction: a biomarker for COVID-19. Int Forum Allergy Rhinol. 2020;10:944–950.
1School of Biological Sciences, Institute for Research in Fundamental Sciences, Tehran, Iran; 2Chronic Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran; 3Clinical Tuberculosis and Epidemiology Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran; 4Smell & Taste Center, Department of Otorhinolaryngology-Head and Neck Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
Correspondence to: Richard L. Doty, PhD, FAAN, Smell & Taste Center, Department of Otorhinolaryngology–Head and Neck, Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA; e-mail: email@example.com
Potential conflicts of interest: R.L.D. is a consultant to Acorda Therapeutics, Eisai Co, Ltd, Merck Pharmaceuticals, the Michael J. Fox Foundation for Parkinson’s Research, and Johnson & Johnson; receives royalties from Cambridge University Press, Johns Hopkins University Press, and John Wiley & Sons, Inc.; he is president of, and a major shareholder in, Sensonics International, a manufacturer and distributor of smell and taste tests,
R ecently there have been numerous reports in the mediathat anosmia occurs in persons who have contracted coronavirus disease 2019 (COVID-19) by exposure to the severe acute respiratory syndrome-coronavirus-2 (SARS- CoV-2) virus. These include 1 published single case report,1
and self-report surveys from Germany,2 Great Britain,3
Iran,4 Italy,5 and the United States,6 with smell loss re- ports ranging from 34% to 68% of COVID-19–positive pa- tients. Otorhinolaryngology authorities have warned that loss of smell and taste, in combination with other symp- toms, appears to be a strong predictor of COVID-19 infection.7,8
To date, validated quantitative olfactory testing has not been performed in a cohort of COVID-19 patients to
including the test used in this study. A. K-T. is a medical advisor to Cobel Darou in Iran. The other authors have nothing to disclose.
Received: 9 April 2020; Revised: 15 April 2020; Accepted: 15 April 2020 DOI: 10.1002/alr.22587 View this article online at wileyonlinelibrary.com.
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Smell dysfunction: a biomarker for COVID-19
verify or determine the true magnitude of their deficits and whether less-than-total loss occurs in some patients. Moreover, the proportion of COVID-19 patients exhibit- ing true olfactory disturbances is unknown. Most studies suggest that, in general, a significant number of persons with smell loss are unaware of their deficit until formal testing9 and that self-reports of both smell and taste abil- ities correlate poorly with the results of quantitative smell and taste tests.10,11
In this case-control study, we administered the Persian version of the 40-item University of Pennsylvania Smell Identification Test (UPSIT)12 to 60 confirmed COVID-19 patients and 60 age- and sex-matched controls to assess the presence, magnitude, and frequency of their olfactory dysfunction. We determined whether the smell loss was related to the sex of the subjects and inquired, for those patients who were aware of their dysfunction before testing, when they first noticed their chemosensory disorder.
Patients and methods Subjects
The age, sex, comorbidities, smoking status, and com- plaints of chemosensory dysfunction of the 120 study par- ticipants are presented in Table 1. The 60 SARS-COV- 2–positive subjects had been admitted with the symptoms of COVID-19 to the Masih Daneshvari Hospital, Tehran, Iran, between March 21, 2020, and March 23, 2020, or March 31, 2020, and April 5, 2020. At the time of the ol- factory testing, all were inpatients in the recovery period of the disease and were ready to be discharged within 4 days. The study was explained in detail to 68 such patents, of which 8 declined to participate (ie, the participation rate was 88%).
The control subjects were from a database of 141 subjects collected in Iran for an earlier study. They were tested in the olfactory laboratory of the Institute for Research in Fun- damental Sciences, Tehran, Iran, and comprised a conve- nience sample obtained from e-mail lists, flyers, and word of mouth. None had influenza or common cold symptoms at the time of testing. The recruitment period for this database (August 8, 2019, to February 13, 2020) preceded the first reported confirmed cases of COVID-19 in Iran (February 19, 2020). A control subject was individually matched as closely as possible to each COVID-19 patient. Exact age matches were possible for 34 subjects, 1-year differences for 22 subjects, and 2-year differences for 4 subjects. In cases where >1 match was possible, the first match in the database sequence was used.
Informed written consent was obtained from each patient and control, and the study protocol was approved by the local ethics committee and the Iranian Ministry of Health (license number IR.SBMU.NRITLD.REC.1399.013). All testing was performed with the highest regard for examiner safety with appropriate personal protective equipment.
TABLE 1. Patient and control subject demographics *
Sample size, n 60 60
Age (years), mean ± SD 46.55 ± 12.17 46.55 ± 12.07 Gender (male/female), n 40/20 40/20
Smoker (current/never), n 2/58 11/49 0.016
Taste/smell complaints, n 21 0 0.001
Asthma 3 0 0.244
Atherosclerosis 0 2 0.496
Autoimmune disease 4 a
Carcinoma 2 b
Congenital melanocytic nevi 1 0 1.000
Diabetes 8 c
Hemophilia 0 1 1.000
Hepatic failure 0 1 1.000
Hyperlipidemia 1 1 1.000
Hypertension 6 c
Hypothyroidism 4 c
Migraine 0 1 1.000
Osteoporosis 0 1 1.000
Sinusitis 2 0 0.496
*Significant p differences indicated in bold. aAutoimmune disease included Behcet’s disease in combination with Crohn’s disease (n = 1), multiple sclerosis (n = 2), and rheumatoid arthritis (n = 1). bProstate and cervical cancers. c Although, in rare cases, changes in dosage and medications may have occurred
during the course of inpatient treatments, most patients remained on their pread- mission medications. COVID-19 = coronavirus disease 2019; SD = standard deviation.
Diagnosis and clinical severity classification of COVID-19 patients
COVID-19 diagnosis was based on the COVID-19 detec- tion protocol of Masih Daneshvari Hospital. All of the patients underwent 16-slice chest computed tomography (CT) imaging (Scope Power Siemens CT Scan, Munich, Ger- many) and had positive chest CT findings.13 Subsequently, the diagnosis of COVID-19 disease was confirmed by quan- titative detection of SARS-CoV-2 RNA using the real-time reverse-transcription polymerase chain reaction (rRT-PCR) in respiratory specimens.14 The RT-PCR assays were per- formed using Sansure Biotech’s 2019-nCoV 30-Minute Nu- cleic Acid Reagent Kits (Sansure Biotech, Inc., Development Zone, Changsha, China). The respiratory specimens were
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collected from the patients’ nasopharyngeal wash/aspirate or nasal aspirate.
COVID-19 clinical severity was classified as mild, mod- erate, or severe according to the Massachusetts General Hospital COVID-19 treatment guidance algorithm.15 Mild clinical COVID-19 presentation was defined as having oxy- gen saturation (SpO2) >90% along with or without risk factors. Moderate clinical COVID-19 presentation was considered for patients who had at least 1 epidemiolog- ical risk factor along with a risk factor in vital signs or laboratory findings at the admission point of time. Pa- tients in the intensive care unit (ICU) or with progres- sive disease were classified as having severe clinical pre- sentation of COVID-19. Epidemiological risk factors in- cluded age >55 years or preexisting pulmonary disease, chronic kidney disease, diabetes with glycated hemoglobin (A1c) >7.6%, history of hypertension or cardiovascular disease or transplant, or immunosuppression or human immunodeficiency virus (HIV). Risk factors of vital signs comprised respiratory rate >24 breaths/minute, heart rate >125 beats/minute, and SpO2 <90% on ambient air. In laboratory findings, fibrin degradation product D-dimer >1000 ng/mL, creatine phosphokinase (CPK) more than twice the upper limit of normal, C-reactive protein (CRP) >100 mg/L, lactate dehydrogenase (LDH) >245 U/L, el- evated troponin, admission absolute lymphocyte count <0.8, and ferritin >300 μg/L. For COVID-19 patients with mild disease with SpO2 >90%, supportive care was provided and hydroxychloroquine administration was started (200 mg twice per day [BID] × 2 doses, then 100 mg BID for 5 days). For the patients with moder- ate to severe COVID-19 presentations, lopinavir/ritonavir 200/50 mg BID for up to 10 days) was prescribed. In patients with progressive COVID-19 disease admit- ted to the ICU, intravenous immunoglobulin (IVIG) at standard dose of 0.5 g/kg/day daily for 5 days was administered.16
Olfactory testing A modified and validated Persian version of the UPSIT was administered in this study (Sensonics International, Had- don Heights, NJ). The UPSIT is a well-validated and reliable (test-retest r = 0.94) test that employs microencapsulated “scratch and sniff” odorants.11,12,17,18 It provides an in- dex of absolute dysfunction (ie, anosmia, severe microsmia, moderate microsmia, mild microsmia, normosmia, malin- gering), as well as relative dysfunction based upon age- and gender-adjusted normative percentile ranks. The to- tal number of odorant stimuli out of 40 that is correctly identified serves as the test measure. Scores on this test correlate well with other types of olfactory tests, includ- ing threshold tests.19 Although the UPSIT is designed to be self-administered, to be certain that the COVID-19 patients correctly performed the test during the limited clinical time window, the testing was assisted by a trained examiner.
FIGURE 1. UPSIT scores of the COVID-19 patients compared to those of healthy controls. The distribution of the participants’ scores in each group is depicted in violin plot. The white circles indicate the median of the score for each group. COVID-19 = coronavirus disease 2019; UPSIT = University of Pennsylvania Smell Identification Test.
Statistical analyses Statistical analyses were performed using either SYSTAT 13 (Systat Software, Inc., San Jose, CA)20 or MATLAB 2019b (The MathWorks, Inc., Natick, MA). A subject group by gender mixed factor analysis of variance (ANOVA) was used to determine whether the UPSIT scores differed signif- icantly between the patient and control groups and whether gender influenced the test scores. Standard ANOVAs were used to compare other means. Differences in frequencies were assessed using the Fisher’s exact probability test.
Results The COVID-19 patients’ non-mutually exclusive present- ing symptoms were fever (n = 46, 77%), cough (n = 35, 58%), shortness of breath (n = 31, 52%), headache (n = 22, 37%), myalgia (n = 5, 8%), sweating (n = 2, 3%), shivering (n = 2, 3%), anorexia (n = 2, 3%), stomachache (n = 1, 2%), and tinnitus (n = 1, 2%). The mean (95% CI) time between the onset of symptoms and the olfactory testsing was 12.76 (11.47, 14.06) days.
The UPSIT testing revealed that, relative to controls and published normative data, the COVID-19 patients exhib- ited marked olfactory dysfunction. Thus, as illustrated in Figure 1, the mean (95% confidence interval [CI]) UP- SIT score for the COVID-19 patients was 20.98 (19.47, 22.48), reflecting severe microsmia,21 whereas the mean UPSIT score (95% CI) for the age- and sex-matched con- trols fell within the normal range (34.10 [33.31, 34.88]; ANOVA group main effect F [1,58] = 232.99, p < 0.0001, η2 = 0.80). The COVID-19 deficit was not specific to any 1 UPSIT odorant, being evident for all 40 stimuli (Fig. 2).
Importantly, all but 1 of the 60 patients with COVID-19 had some degree of measured olfactory dysfunction (98%). Thirty-five of the 60 patients (58%) were either anosmic
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FIGURE 2. Performance on individual UPSIT odorants for the COVID-19 patients and matched healthy controls. Note that dysfunction was evident for all 40 UPSIT odorants. Performance for each group is calculated as the percent of individuals having correctly identified the odorant. COVID-19 = coronavirus disease 2019; UPSIT = University of Pennsylvania Smell Identi- fication Test.
TABLE 2. Classification of olfactory function of the UPSIT scores of COVID-19 patients and matched controls
UPSIT function category
patients n (%)
Normosmia 1 (2) 49 (82) 31–40
Mild microsmia 8 (13) 11 (18) 28–30
Moderate microsmia 16 (27) 0 24–27
Severe microsmia 20 (33) 0 17–23
Anosmia 15 (25) 0 6–16
Probable malingering 0 0 0–5
COVID-19 = coronavirus disease 2019; UPSIT = University of Pennsylvania Smell Identification Test.
(15/60; 25%) or severely microsmic (20/60; 33%); 16/60 (27%) exhibited moderate microsmia, 8/60 (13%) mild mi- crosmia, and 1/60 (2%) normosmia according to Persian- adjusted UPSIT norms (Table 2).21 This contrasts markedly from the controls, of which 49 of 60 (82%) were normal with the remaining 11 of 60 (18%) having only mild bor- derline dysfunction. Relative to the normal controls, the 11 controls with mild borderline dysfunction tended to be disproportionately men (10/11 [91%] vs 30/49 [61%]; p = 0.08) of older age (respective mean ages [95% CIs] = 51.18 [42.63, 59.73] and 45.51 [42.11, 48.90]; p = 0.18). Even though there was a tendency for women, overall, to outper- form men on the UPSIT (respective mean [95% CI] UPSIT scores: 22.55 [20.13, 24.97] and 20.20 [18.27, 22.13]; F [1,58] = 3.82, p = 0.055, η2 = 0.06), this was unrelated to COVID-19 (sex by group interaction F [1,58] = 0.396, p = 0.53).
Thirty-five percent (21/60) of the COVID-19 patients re- ported a loss in either smell or taste function, with 12% (7/60) reporting smell loss only, 7% (4/60) taste loss only,
TABLE 3. Relationship between COVID-19 clinical disease severity and mean (95% CI) scores on the UPSIT
COVID-19 disease severity n (%)
Mild 25 (42) 22.04 (20.11–24.72)
Moderate 29 (48) 19.69 (17.24–21.99)
Severe 6 (10) 22.83 (17.65–25.77)
CI = confidence interval; COVID-19 = coronavirus disease 2019; UPSIT = Univer- sity of Pennsylvania Smell Identification Test.
and 17% (10/60) both taste and smell loss. There was no significant difference between UPSIT scores of patients who were aware or unaware of their chemosensory loss (p = 0.28). All 21 reported that the onset of the olfactory dys- function occurred at the same time or immediately after the onset of their other COVID-19 symptoms. None reported recognizing any smell or taste deficits prior to their other COVID-19 symptoms, namely fever, cough, or shortness of breath. In the healthy control group, none of the partic- ipants reported any smell or taste problems.
As shown in Table 1, significantly fewer smokers were present in the COVID-19 group than in the control group (2/60 vs 11/60; p = 0.016). Eight patients with diabetes were present in the COVID-19 group, unlike the control group (8/60 vs 0/60; p = 0.007). However, the respective mean (95% CI) UPSIT scores for COVID-19 patients with and without diabetes did not differ (21.38 [18.18, 24.56] vs 20.92 [19.32, 22.62], respectively; F [2,57] = 1.43, p = 0.24, η2 = 0.05). No association of UPSIT scores with disease severity, as per the Massachusetts General Hospi- tal COVID-19 treatment guidance algorithm, was apparent (Table 3; F [2,57] = 1.45, p = 0.24, η2 = 0.05).
Discussion This study quantitatively evaluated olfaction in a sizable cohort of patients diagnosed with the SARS-CoV-2 virus infection. By employing a well-validated 40-item smell test, COVID-19 patients were able to be classified into dis- tinct categories of olfactory dysfunction, with 35 of 60 (58%) exhibiting either anosmia or severe microsmia. In the present study, only 35% of the patients were aware of their olfactory deficit before testing, a percentage near to that of 34% reported in an interview with COVID-19 inpatients in Italy,5 but lower than those reported in 2 on- line surveys (59%3 and 68%6). This difference between self-report rate and quantified smell assessment conceiv- ably reflects a disproportionate sampling of hospital ad- mitted cases and/or the well-documented underestimation of self-reported smell and taste dysfunction present for the general population9,10 and for such diseases as Alzheimer’s disease (AD)11 and Parkinson’s disease (PD).22,23 In gen- eral, smell loss is most noticeable when marked loss, such as anosmia, is present.11,22 It should be pointed out that
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the present study’s sample resembles the demographic and clinical characteristics of COVID-19 patients reported in a compilation of 43 studies involving 3600 patients,24
implying it is likely representative of COVID-19 patients in general.
The basis for the smell loss due to SARS-CoV-2 is not entirely clear, although it is well established that viruses and other xenobiotics can damage the olfactory neuroep- ithelium. Indeed, acute viral upper respiratory viral infec- tions that damage this epithelium are the major cause of chronic olfactory dysfunction and numerous viruses are known to enter the brain through cellular and pericellular transport via this epithelium.25 In North America, the peak period of non-influenza–related smell loss, including that possibly due to coronaviruses, occurs during the months of April, May, and June, whereas influenza-related smell loss peaks in December, January, and February.26 Currently, the prevalence of COVID-19 in North America seems to follow a similar function to that observed for olfactory deficits due to other viruses, including other coronaviruses. What seems unique, however, is that nearly everyone who contacts COVID-19 appears to exhibit measurable loss of smell seemingly independent of severe nasal congestion or inflammation.