Table 3.
Summary of smell-related outcomes assessed via validated questionnaires and/or objective tests
| Study authors | Patient age (years) | Setting | Olfactory evaluation(s) | Evaluation time point | Evaluation results | Olfactory dysfunction onset |
|---|---|---|---|---|---|---|
| Carignan et al.18 | Median 57.1; IQR 41.2–64.5 | Out-patients (except 3 Covid-19 patients admitted to hospital) | Adapted questions from Self-reported Mini Olfactory Questionnaire47 | Within 72 hours’ (before or after) SARS-CoV-2 testing | Anosmia 69 (51.5%), dysgeusia 85 (63.4%) | 3 (2.2%) reported anosmia & dysgeusia as presenting manifestations |
| Hornuss et al.20 | Median 56 ± 16.9 | In-patients | Self-report questionnaire, Burghart Sniffin’ Sticks smell test48,49 | N/A | 44% of anosmic & 50% of hyposmic patients on objective tests did not report smelling problems | N/A |
| Lechien et al.24 | Average 36.9 ± 11.4; IQR 19–77 | Non-ICU in-patients & infected healthcare workers across Europe | sQOD-NS50 | Average of 9.2 ± 6.2 days after first symptoms onset | Anosmia 284, 73 hyposmia | Olfactory dysfunction appeared before (11.8%), after (65.4%) or at same time as appearance of general or ENT symptoms (22.8%) |
| Lechien et al.25 | Average 39.50; IQR 12.10 | 161 (8%) in-patients & 1852 (92%) out-patients | Standardised online validated questionnaire NAHNES;51 a subset of patients had Burghart Sniffin’ Sticks smell test48,49 | Mean (SD) time from end of disease to evaluation was 7.8 (6.8) days | Mean duration of olfactory dysfunction was 8.4 days (SD, 5.1) | Before other symptoms (15%), concomitant with other symptoms (25%) or after other symptoms (57%) (considering patients with smell dysfunction) |
| Lechien et al.26 | Mean 41.7 ± 11.8 | Out-patients | NAHNES,51 sQOD-NS,50 SNOT-22 (French version), Burghart Sniffin' Sticks smell test48,49 | Mean duration of olfactory dysfunction at evaluation time was 17 ± 11 days for anosmic & 18 ± 11 days for hyposmic patients | Objective olfactory testing: 41 (47.7%) anosmic, 12 (14.0%) hyposmic | 61.4% of patients described total loss of smell at disease onset |
| Li et al.29 | Average 49 (range, 13–80) | Multicentre prospective cohort study | Smell identification testing using a T&T olfactometer based scoring system52 with odours generally familiar to Chinese population | N/A | Dysosmia of: garlic in 7 (5%), pineapple in 13 (9%), mint in 11 (8%) & ginger in 38 (26%) | Average from symptom onset of 62 days (range, 25–95) |
| Moein et al.32 | Average 46.55 ± 12.17 (overall population) | In-patients in single hospital | UPSIT smell test,53 single question | Patients dismissible within 4 days | Anosmia in 15; microsmia was severe in 20, moderate in 16 & mild in 8 | N/A |
| Ottaviano et al.34 | N/A | N/A | Objective olfactory test ‘Le Nez Du Vin’ quick olfaction test,54 PROMs,34 SNOT-22,55 smell & taste VAS55 | N/A | Alterations in smell & taste; nasal symptoms other than olfaction or taste were found to be irrelevant | N/A |
| Spinato et al.37 | Median 56; IQR 45–67 | Out-patients in single hospital | ARTIQ,56 SNOT-2255 | Patients were asked if had experienced sudden onset of altered smell or taste in 2 weeks before swab | SNOT-22 grades: 5 very mild, 23 mild, 27 moderate, 27 severe, 48 as bad as it can be | Timing of altered sense of smell or taste onset in relation to other symptoms occurred before other symptoms in 24 (11.9%), at same time in 46 (22.8%) & after other symptoms in 54 (26.7%) |
| Tsivgoulis et al.40 | Mean 55 ± 10 | In-patients | SNOT-22,55 Q-SIT (Sensonics, Haddon Heights, NJ, USA)57 | N/A | Microsomia in 15, anosmia in 1 | N/A |
| Vaira A et al.41 | Average 48.5 ± 12.8 (range, 23–88) | 184 in-patients & 161 out-patients | CCCRC orthonasal olfaction test58,59 administered for hospitalised patients; test with 7 groups of odorants for home-quarantined patients | 9.9 ± 5.8 (range, 1–28) days from positive swab; 14.8 ± 7.4 (range, 2–35) days from Covid-19 symptoms onset | Normal findings in 104 (30.1%); hyposmia was mild in 76 (22%), moderate in 59 (17.1%), severe in 45 (13%); anosmia in 61 (17.7%) | High frequencies of olfactory disorders throughout observation period, ranging between 77.4% (days 1–4) & 69.2% (days 25–35) |
| Vaira et al.42 | Average 49.2 ± 13.7 (range, 26–90) | In-patients in single teaching hospital & infected healthcare workers | CCCRC orthonasal olfaction test,58,59 single questions | Average 19.3 ± 4.5 days from onset; 15.6 ± 4.3 days from positive swab. Prevalence over whole disease course | Hypogeusia was mild in 22, moderate in 33, severe in 3; ageusia in 2; olfactory dysfunction in 44 | N/A |
| Vaira et al.43 | Average 47.2 ± 10 (range, 26–64) | Out-patients in 3 hospitals | CCCRC orthonasal olfaction test,58,59 self-administered home test, single questions | Average 20.1 ± 3.9 days from onset; 17.5 ± 3.1 days from positive swab. Prevalence over whole disease course | Of 21 with chemosensory dysfunctions, 4 had hyposmia only, 4 had anosmia hyposmia only, & 13 reported olfactory & taste disorders | N/A |
IQR = interquartile range; Covid-19 = coronavirus disease 2019; SARS-CoV-2 = severe acute respiratory syndrome coronavirus-2; N/A = not applicable; ICU = intensive care unit; sQOD-NS = short version of the Questionnaire of Olfactory Disorders – Negative Statements (a seven-item patient-reported outcome questionnaire including social, eating, annoyance and anxiety questions; NAHNES = National Health and Nutrition Examination Survey; SD = standard deviation; UPSIT = University of Pennsylvania Smell Identification Test; PROM = patient-reported outcome measures; SNOT-22 = Sino-Nasal Outcome Test-22; VAS = visual analogue scale; ARTIQ = Acute Respiratory Tract Infection Questionnaire; Q-SIT = Quick Smell Identification Test; CCCRC = Connecticut Chemosensory Clinical Research Center