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. 2020 May 23;277(9):2625–2630. doi: 10.1007/s00405-020-06069-6

The role of self-reported smell and taste disorders in suspected COVID‑19

Athanasia Printza 1,, Jannis Constantinidis 1
PMCID: PMC7245504  PMID: 32447496

Abstract

Purpose

The sudden onset of smell and taste loss has been reported as a symptom related to COVID-19. There is urgent need to provide insight to the pandemic and evaluate anosmia as a potential screening symptom that might contribute to the decision to test suspected cases or guide quarantine instructions.

Methods

Systematic review of the PubMed/Medline, Cochrane databases and preprints up to May 3, 2020. Combined search terms included: “COVID-19”, “SARS-CoV-2”, “coronavirus”, “nose”, “anosmia”, “hyposmia”, “olfactory loss”, “smell loss”, “taste loss”, and “hypogeusia”.

Results

Our search identified 18 reviewed articles and 6 manuscript preprints, including a large epidemiological study, four observational case series, five case–controlled studies, five cross-sectional studies, five case series of anosmic patients and four electronic surveys. Great methodological differences were noted. A significant prevalence of anosmia is reported in COVID-19 patients. Controlled studies indicate that anosmia is more common in COVID-19 patients than in patients suffering from other viral infections or controls. Most of the studies reported either smell loss or smell plus taste loss. Less severe COVID-19 disease is related to a greater prevalence of anosmia. A quick recovery of the smell loss may be expected in most COVID-19 cases.

Conclusion

Anosmia is more prevalent in COVID-19 patients than in patients suffering from other respiratory infections or controls.

Keywords: Anosmia, COVID-19, Olfactory dysfunction, Loss of smell, SARS-CoV-2, Taste


Since the outbreak of the COVID‑19 pandemic, observations and scientific reports have been accumulating rapidly that sudden anosmia and taste disorders are symptoms associated with the COVID-19 infection [1, 2]. Recently the World Health Organization has included the loss of smell or taste as a new symptom of COVID-19 infection as have many Health Authorities after a surge of publications and press releases that pointed to anosmia as a potential screening symptom that might contribute to the decision to test suspected cases or guide quarantine instructions. Subsequently, Otolaryngologic and Rhinologic Societies have worldwide also advised to consider patients with newly acquired sudden loss of smell as potentially positive for SARS-CoV-2. Given the increase of publications concerning anosmia, and the fact that most current research is under “time-pressure” to provide insight to the pandemic, we undertook a review of the published relevant literature. The objective of this systematic review was to examine existing scientific evidence on the role of anosmia detection in the COVID-19 pandemic and highlight the areas of need for further research.

A computerized search of the PubMed/Medline and Cochrane databases was performed of all indexed studies to identify all relevant manuscripts and preprints up to May 3, 2020. Preprints’ repositories included medRxiv. Combined search terms included: “COVID-19”, “SARS-CoV-2”, “coronavirus”, “nose”, “anosmia”, “hyposmia”, “olfactory loss”, “smell loss”, “taste loss”, and “hypogeusia”. Adjunctive searches were performed based on the studies that were identified (and their references). Studies were excluded if full texts could not be obtained.

Our search identified 18 reviewed articles published or accepted for publication [118] and 6 manuscript preprints (not peer-reviewed) [1924] reporting on patients presenting sudden anosmia/taste loss in the context of COVID-19 infection (Table 1). The studies took place from mid-January to mid-April. There were great methodological differences among the studies. A large epidemiological study reported on 9199 persons who were recruited for targeted testing in Iceland [9]. Four large observational case series reported anosmia prevalence in COVID-19 cohorts from China [3], Belgium and other European countries [2], USA [8], Italy [11]. Five case–controlled studies compared the smell/taste loss between SARS-CoV-2 PCR-positive participants and patients PCR-positive for influenza [4], a panel of respiratory viruses [10], matched hospitalized controls [6, 20], and patients tested for influenza-like symptoms for COVID-19 [19]. Five cross-sectional studies of SARS-CoV-2 + patients report on smell/taste loss in patients with varying COVID-19 disease severity [1, 5, 7, 21, 22]. Four small case series and a case report of anosmic patients, most of whom had been tested for SARS-CoV-2 with various indications [1418] and four electronic surveys about smell loss [12, 13, 23, 24] commented on the increase of the patients seeking treatment for smell loss during the COVID-19 pandemic. The electronic surveys included the AAOHNS COVID-19 Anosmia Reporting Tool (completed by healthcare providers) [12], The RADAR COVID-19, an online app for the UK general population [23] and two surveys prompted by patients’ queries about smell loss (in UK [13] and Iran [24]), one reporting on a small percentage tested for SARS-CoV-2.

Table 1.

Studies on the role of smell and taste disorders in suspected COVID‑19

Author source Country Study type No of patients Participants Anosmia % Course of anosmia Level of evidence

Giacomelli A, et al. [1]

Clin Infect Dis

Italy

Cross-sectional 59 SARS-CoV-2+, hospitalized

33.9% taste/smell loss

18.6% both

20.3% pre-admission anosmia IV

Lechien et al. [2]

Eur Arch Otorhinolaryngol

Belgium

France

Italy, Spain

Case series observational 417 mild-to-moderate COVID-19 SARS-CoV-2+, hospitalized and home

85.6% smell loss

79.6% anosmic

11.8% initial symptom

Taste loss in 88.8%

72.6% recovered smell in 8 d

IV

Mao L, et al. [3]

JAMA Neurol China

Case series, observational 214 SARS-CoV-2+, hospitalized

5.1%

6.3% in mild disease

5.6% taste loss IV

Beltrán-Corbellini Α, et al. [4]

Eur J Neurol

Spain

Case-control

79 COVID-19

40 controls

SARS-CoV-2+, hospitalized

influenza controls

31.6% in COVID-19

12.5% in controls (OR 21.4)

35.5% initial symptom

35.4% taste loss

12.9% nasal obstruction

56.7% recovery (mean: 7.5 d)

III

Spinato J, et al. [5]

JAMA

Italy

Cross-sectional 202 SARS-CoV-2+, home 64.4%

3% only symptom

36.1% nasal obstruction

IV

Moein ST, et al. [6]

Int Forum Allergy Rhinol

Iran

Case–control

60 patients

60 controls

SARS-CoV-2+, hospitalized

matched controls olfactory test

29% reported a loss

58% tested anosmic/severely hyposmic

18% of controls mild hyposmia

Not an initial symptom

24% taste loss

III

Yan CH, et al. [7]

Int Forum Allergy Rhinol

USA

Cross-sectional

59 SARS-CoV-2+

203 SARS-CoV-2−

suspect case

SARS-CoV-2+ mostly home

68% in SARS-CoV-2+

16% in SARS-CoV-2−

Taste loss

71% in SARS-CoV-2+

17% in SARS-CoV-2−

72.5% improvement

18% < 1 W, 37.5% 1–2 W

IV

Yan CH, et al. [8]

Int Forum Allergy Rhinol

USA

Case series, observational 128 SARS-CoV-2+,20% hospitalized

26.9% in hospitalized patients

66.7% in home-treated patients

Taste loss

23.1% in hospitalized vs 62.7% in home-treated

Patients with loss of smell were 10 times less likely to be admitted

IV

Gudbjartsson DF, et al. [9]

N Engl J Med

Iceland

Epidemiological 1044

Targeted Tests

SARS-CoV-2+

11.5% High level epidemiological

Wee LE, et al. [10]

Eur Arch Otorhinolaryngol

Singapore

Case-control

870 suspect case

154 SARS-CoV-2+

71 other viruses+, rhinovirus, influenza, adenoviruses, coronaviruses

Suspect cases

SARS-CoV-2+ routine panel of respiratory viruses

5% in suspect cases

22.7% in SARS-CoV-2+

2.8% in other viruses (OR 10.14)

8.6% only symptom

28.5% rhinorrhea

Smell loss as screening:

98.7% specificity, 22.7% sensitivity

III

Vaira LA, et al. [11]

Head Neck

Italy

Case series observational 72

SARS-CoV-2+

22 hospitalized

47 home, healthcare personnel

Olfactory/taste test

73%

18% initial symptom

66% recovery at evaluation (mean 19 d) most recovered earlier than 5 d

IV

Kaye R, et al. [12]

Otolaryngol Head Neck Surg

USA

Online AAOHNS Reporting Tool 237 physician-submitted cases of COVID-19 related smell/taste loss The AAOHNS COVID-19 Anosmia Reporting Tool All

27% initial symptom

25% nasal obstruction

18% rhinorrhea

Mean time to improvement of 7.2 d

IV

Hopkins C, et al. [13]

Rhinology

UK

Survey prompted by queries about anosmia 2428 reporting new onset anosmia 80 had been tested for SARS-CoV-2, 74% were positive All IV

Heidari F, et al. [14]

Rhinology

Iran

Anosmia case series 23 Sudden anosmia SARS-CoV-2+ All

83% initial symptom

69.6% only symptom

75% improvement in 2 weeks

IV

Gilani G, et al. [15]

Medical Hypothesis

Iran

Anosmia case series 8

Sudden anosmia

5 tested, SARS-CoV-2+

All Anosmia followed other symptoms IV

Ottaviano G, et al. [16]

Rhinology

Italy

Anosmia case series 6 healthcare personnel

Sudden anosmia

SARS-CoV-2+

All

75% initial symptom

Improvement in 15 d

IV

Gane SB, et al. [17]

Rhinology

UK

Anosmia case series 11 Sudden anosmia 1 tested, SARS-CoV-2+ All 55.5% only symptom IV

Eliezer M, et al. [18] JAMA Otolaryngol Head Neck

France

Case report 1 SARS-CoV-2+ CT, MRI Anosmia without nasal obstruction Bilateral inflammatory obstruction of the olfactory clefts IV

Haehner A, et al. [19]

medRxiv

Germany

Cross-sectional controlled

500 suspect cases

34 SARS-CoV-2+

466 SARS-CoV-2−

Suspect cases

Anosmic were 22 SARS-CoV-2+

49 SARS-CoV-2−

13.8% in all suspect cases

64.7% in SARS-CoV-2+

10.1% in SARS-CoV-2−

Anosmic pts had less severe COVID-19

4.5% initial symptom

COVID-19 anosmic patients had less nasal obstruction and rhinorrhea

Smell loss as screening:

65% sensitivity, 90% specificity

III

Hornuss D, et al. [20]

medRxiv

Germany

Cross-sectional controlled

45 patients

45 controls

SARS-CoV-2 + , hospitalized

Hospitalized controls

Olfactory test (Sniffin’ Stick12)

SARS-CoV-2+

49% reported smell loss

Tested anosmic 40%, hyposmic 40%

0% of controls reported anosmia

III

Levinson R, et al. [21]

medRxiv

Israel

Cross-sectional 42 SARS-CoV-2+ hospitalized mild COVID-19 35.7%

33.3% taste loss

Anosmia follow-up/4d: 73.3% recovery, median duration 7.6 d

IV

Lechien J, et al. [22]

medRxiv

Belgium

Cross-sectional

78 reporting sudden anosmia

49 SARS-CoV-2+

Sudden anosmia

SARS-CoV-2+

Olfactory test, 46pts

All

Anosmia ≤ 12 d:

87.5% SARS-CoV-2+

Lasting: 23% SARS-CoV-2+

46.2% nasal obstruction

24% of reported anosmic patients were normosmic on olfactory testing

IV

Menni C, et al. [23]

medRxiv

UK

Online app

Community survey

For general population

1702 responders reported having being tested

579 SARS-CoV-2+

1123 SARS-CoV-2−

Responders to RADAR COVID-19, an app asking about COVID-19 symptoms

59% in SARS-CoV-2+

18% in SARS-CoV-2−

IV

Bagheri SHR, et al. [24]

medRxiv

Iran

Online community survey 10069 reporting new onset anosmia Volunteers reporting anosmia, general population Anosmia increased as did COVID-19 positivity in provinces of Iran IV

No number; Level of evidence of prognostic studies; d days; w weeks; AAOHNS American Academy of Otolaryngology–Head and Neck Surgery; tested: with RT-PCR for SARS-CoV-2+

Prevalence of smell loss: A large epidemiological study reported a prevalence of 11.5% for smell loss in 1044 SARS-CoV-2 + identified through targeted tests [9]. Four observational case series reported smell loss in their studied cohorts at 5.1% (hospitalized patients) [3], 26.9% (hospitalized patients) and 66.7% (home-treated patients) [8], 73% (hospitalized and home-treated patients) [11], and 85.6% (hospitalized and home-treated patients) [2]. The observed discrepancies most likely are related to varying research methods and possible patient selection biases. A significant proportion of the cohort in the studies reporting high anosmia prevalence was healthcare personnel [2, 11]. Cross-sectional studies found the prevalence of anosmia to be at 33.9% [1] and 35.7% [21] for hospitalized patients and 64.4% [5] and 68% [7] for out-patients. Smell loss prevalence was compared between COVID-19 patients and control groups in five case-controlled studies: 22.7% of COVID-19 patients compared to 2.8% of patients positive for a panel of respiratory viruses [10], 31.6% of COVID-19 compared to 12.5% of influenza [4], 29% of COVID-19 patients compared to 18% for controls [6], 49% compared to 0% for controls [20], and 64.7% of COVID-19 patients compared to 10.1% for respiratory viral illness [19]. The smell loss as a screening symptom was found to show a high specificity and moderate sensitivity for the detection of COVID-19 infection [10, 19].

Clinical characteristics: Most of the studies reported either smell loss or smell plus taste loss. As a presenting symptom, anosmia was rated from 0 to 35%. All the studies that comment on the course of anosmia report quick recovery, in 7–10 days [2, 4, 7, 11, 14, 16, 21]. Nasal obstruction was found at rates ranging from 12.9% to 46% and rhinorrhea from 18% to 28.5%.

While great methodological differences were noted in the reviewed studies, a significant prevalence of anosmia is reported in COVID-19 patients, and controlled studies indicate that anosmia is more common in COVID-19 patients than in patients suffering from other respiratory infections or controls, taking into account seasonal patterns of olfactory dysfunction. Less severe COVID-19 disease is related to a greater prevalence of anosmia. Olfactory testing and treatment decisions should take into account that quick recovery of the smell loss may be expected in most COVID-19 cases.

Compliance with ethical standards

Conflict of interest

The authors have no conflicts of interest.

Footnotes

Publisher's Note

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