Table I.
Features of the studies using self-rating assessment.
| Source | Year | Country | Study population | Methods | Prevalence | Recovery time | Topic | STROBE score* | |
|---|---|---|---|---|---|---|---|---|---|
| 1 | Altundag A 13 | 2021 | Turkey, USA | 135 COVID-19 patients | Structured questionnaire | OD: 59.3%; Mean recovery: 7.8 days | N/A | Prevalence and recovery of chemosensory dysfunction | 20 |
| 2 | Bagheri SH 14 | 2020 | Iran | 10 069 COVID-19 patients | Structured questionnaire | OD: anosmia 60.9%, 80.4% combined dysfunction | N/A | Prevalence of chemosensory dysfunction | 20 |
| 3 | Barillari MR 15 | 2020 | Italy | 294 COVID-19 patients | Validated questionnaires | OD: 70.4%; GD: 59.2% | N/A | Prevalence of chemosensory dysfunction | 21 |
| 4 | Boscolo Rizzo P 16 | 2021 | Multicentric | 268 COVID-19 patients | Validated questionnaires | Combined chemosensory dysfunction: 81.3%; OD: 10.2%; GD 8.6% | N/A | Prevalence of chemosensory dysfunction | 22 |
| 5 | Boscolo-Rizzo P 18 | 2020 | Italy, UK | 187 COVID-19 patients | Validated questionnaires | Baseline: - OD or GD: 60.4%; 4 weeks: - complete resolution or improvement: 89% | N/A | Prevalence of chemosensory dysfunction and recovery time | 21 |
| 6 | Boscolo-Rizzo P 17 | 2020 | Italy | 296 household contacts of home-isolated COVID-19 patients | Structured questionnaire | OD or GD: 25% | N/A | Prevalence of chemosensory dysfunction | 21 |
| 7 | Chapurin N 19 | 2021 | USA | 1003 COVID-19 patients | Validated questionnaires | OD and GD: 73% | 19.7 days | Prevalence of chemosensory dysfunction | 20 |
| 8 | Chiesa-Estomba CM 20 | 2020 | Multicentric | 751 COVID-19 patients | Validated questionnaires | OD: 82.7%; anosmia 83%, hyposmia 17% | N/A | Prevalence and recovery of chemosensory dysfunction | 22 |
| 9 | Cho RHW 21 | 2020 | Hong Kong | 83 COVID-19 patients; 60 controls | Structured questionnaire | OD: 47%; GD: 43.4% | OD: 10.3 days; GD: 9.5 days | Correlation between olfactory dysfunction and viral load | 22 |
| 10 | Gerkin RC 22 | 2021 | Multicentric | 4148 COVID-19 patients | Validated questionnaires; VAS | N/A | N/A | Predictive value of olfactory loss in COVID-19 | 22 |
| 11 | Gorzkowski V 23 | 2020 | France | 229 COVID-19 patients | Structured questionnaire | OD: 70.3% | 11.6 days | Prevalence of chemosensory dysfunction and recovery time | 22 |
| 12 | Haehner A 24 | 2020 | Germany | 500 patients suspected for COVID-19: 34 confirmed cases | Structured questionnaire; VAS for OD/GD | Smell and/or taste loss: 13.8% | N/A | Predictive value of olfactory loss in COVID-19 | 19 |
| 13 | Hopkins C 25 | 2021 | Multicentric | 434 responders; 114 COVID-19 patients | Structured questionnaire | 6 months: 40.9% patients normosmic; 97.2% normogeusic | N/A | Prevalence of chemosensory dysfunction | 20 |
| 14 | Iravani B 26 | 2020 | Multicentric | 2440 patients | Data collection website smelltracker.org | Relationship between the COVID-19 prediction model and odour intensity ratings over time, ρ = -0.83, P < 0.001 | N/A | Predictive value of olfactory loss in COVID-19 | 21 |
| 15 | Jalessi M 27 | 2021 | Iran, UK | 243 COVID-19 patients | Validated questionnaires | OD: 88.5% anosmia at the onset. | N/A | Prevalence of chemosensory dysfunction | 20 |
| 16 | Konstantinidis I 28 | 2020 | Greece | 79 COVID-19 patients | VAS; olfactory and gustatory home test | OD: 36.7%; GD: 27.8% | N/A | Prevalence of chemosensory dysfunction | 22 |
| 17 | Lal P 83 | 2021 | India | 435 COVID-19 patients | Structured questionnaire | OD and/or GD: 10.8% | - OD 12.1 days; - GD 10.8 days | Recovery time | 15 |
| 18 | Lechien JR 29 | 2020 | Multicentric | 417 COVID-19 patients | Validated questionnaires | OD: 85.6%. GD: 88.0% | N/A | Prevalence of chemosensory dysfunction | 21 |
| 19 | Lechien JR 32 | 2021 | Multicentric | 2581 COVID-19 patients | Validated questionnaires; Sniffin’ sticks identification test (233 patients) | OD: 85.9% (mild forms) moderate-to-critical forms (4.5-6.9%). Psychophysical testing: 54.7% hyposmia/anosmia | - OD 21.6 days | Prevalence and recovery of chemosensory dysfunction | 20 |
| 20 | Lechien JR 31 | 2021 | Multicentric | 2579 COVID-19 patients | Validated questionnaires; Sniffin’ sticks identification test (231 patients) | OD: 73.7%. GD: 46.8%. Psychophysical testing: 23.5% anosmia; 18.6% hyposmia | N/A | Prevalence of chemosensory dysfunction | 20 |
| 21 | Lechien JR 30 | 2020 | Multicentric European | 1420 COVID-19 patients | Validated questionnaires | OD: 70.2%; GD: 54.2% | N/A | Prevalence of chemosensory dysfunction | 20 |
| 22 | Locatello LG 33 | 2021 | Italy | 101 COVID-19 patients | Validated questionnaires | Chemosensory dysfunction; - One month: 44%; -Three months: 37% | N/A | Treatment outcomes | 21 |
| 23 | Lucidi D 34 | 2020 | Italy | 110 COVID-19 patients | Validated questionnaires | N/A | Complete recovery: 7-14 days in 63% patients. Partial recovery: 1-3 months in 22% patients | Prevalence of chemosensory dysfunction | 20 |
| 24 | Maiorano E 35 | 2021 | Italy | 170 COVID-19 patients | Structured questionnaire; VAS for OD/GD | OD and GD: 96% | N/A | Prevalence of chemosensory dysfunction | 19 |
| 25 | Paderno A 36 | 2020 | Italy | 508 COVID-19 patients | Structured questionnaire | OD: 56%; GD: 63% | N/A | Prevalence of chemosensory dysfunction | 22 |
| 26 | Parma V 37 | 2020 | Multicentric | 4039 COVID-19 patients | Validated questionnaires | Mean reduction of smell: -79.7%; taste: -69.0%; chemestetic: -37.3% | N/A | Prevalence of chemosensory dysfunction | 22 |
| 27 | Qiu C 38 | 2020 | Multicentric | 394 COVID-19 patients | Validated questionnaires, VAS | Olfactory and/or gustatory dysfunction: 41% | N/A | Prevalence of chemosensory dysfunction | 22 |
| 28 | Raad N 39 | 2021 | Iran | 1299 COVID-19 patients | Validated questionnaires | Parosmia: 10.8% | N/A | Prevalence of parosmia | 20 |
| 29 | Spinato G 40 | 2021 | Italy | 230 COVID-19 patients; 230 controls | Validated questionnaires | N/A | N/A | Validation of a questionnaire | 21 |
| 30 | Vaira LA 41 | 2021 | Multicentric | 153 COVID-19 patients after vaccination | Validated questionnaires | OD: 62.3%. GD: 53.6% | N/A | Prevalence of chemosensory dysfunction in COVID-19 cases after vaccination | 21 |
| 31 | Yan CH 42 | 2020 | USA | 128 COVID-19 patients | Structured questionnaire | OD: -hospitalized 26.9%, outpatients 66.7%; GD: -hospitalized 23.1%, outpatients 62.7% | N/A | Predictive value of olfactory loss in COVID-19 | 19 |
OD: indicates olfactory dysfunction; GD: gustatory dysfunction; N/A: not applicable; VAS: visual analogue scale.
* Scores interval from 0 to 22, with higher scores showing better study quality 12.