TABLE I.
Major Characteristics of the Included Studies.
| No. | Study IDReference | Study Design | Country | Data Collection Period | Total Number of COVID‐19 Patients (Female) | Age (years) (Mean ± SD/Median (IQR)/Range | COVID‐19 Confirmation Procedure | Type of Assessment for Olfactory Dysfunction (Subjective/Objective) | Method of Assessment for Olfactory Dysfunction |
|---|---|---|---|---|---|---|---|---|---|
| 1 | Abalo‐Lojo 2020 16 | Cross‐sectional | Spain | NR | 131 (75) | 50.4 ± NR | RT‐PCR | Subjective | Self‐reported |
| 2 | Agarwal 2020 17 | Cross‐sectional | USA | 1 March–4 April 2020 | 16 (4) | 67.0 (38.0–95.0) | RT‐PCR | NR | NR |
| 3 | Alshami 2020 18 | Cross‐sectional | Saudi Arabia | 16 March–18 April 2020 | 128 (69) | 39.6 ± 15.5 | RT‐PCR | Subjective | Telephone questionnaire survey |
| 4 | Altin 2020 19 | Case–control | Turkey | 25 March–20 April 2020 | 81 (40) | 54.1 ± 16.9 | RT‐PCR | Objective | Sniffin' Sticks test |
| 5 | Beltrán‐Corbellini 2020 20 | Case–control | Spain | 23–25 March 2020 | 79 (31) | 61.6 ± 17.4 | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 6 | Biadsee 2020 21 | Cross‐sectional | Israel | 25 March–15 April 2020 | 128 (70) | 36.2 ± NR | RT‐PCR | Subjective | Telephone questionnaire survey |
| 7 | Brandsetter 2020 22 | Cross‐sectional | Germany | NR | 31 (26) | 18.0–65.0 | RT‐PCR | Subjective | Self‐reported |
| 8 | Carignan 2020 23 | Case–control | Canada | 10–23 March 2020 | 134 (81) | 57.2 (42.6–64.4) | RT‐PCR | Subjective | Telephone interview |
| 9 | Cervilla 2020 24 | Cross‐sectional | Spain | March–May 2020 | 51 (44) | 43.8 ± 10.7 | RT‐PCR | Subjective | Telephone questionnaire survey |
| 10 | Chary 2020 25 | Cross‐sectional | France | 25 March–18 April 2020 | 115 (81) | 47.0 (20.0–83.0) | RT‐PCR | Subjective | Telephone interview |
| 11 | Chiesa‐Estomba 2020 26 | Cross‐sectional | Spain, Uruguay, Argentina, and Venezuela | NR | 542 (324) | 34.0 ± 11.0 | RT‐PCR | Subjective | Online questionnaire survey |
| 12 | Chiesa‐Estomba 2020a 27 | Cross‐sectional | Spain, Belgium, France, Canada, and UK | NR | 751 (477) | 41.0 ± 13.0 | RT‐PCR | Subjective | Online questionnaire survey |
| 13 | Chua 2020 28 | Cross‐sectional | Singapore | 23 March–4 April 2020 | 31 (NR) | NR | RT‐PCR | Subjective | Self‐reported |
| 14 | D'Ascanio 2020 29 | Cross‐sectional | Italy | 1 February–24 April | 43 (14) | 58.1 ± 15.7 | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 15 | Dawson 2020 30 | Cross‐sectional | USA | March–April 2020 | 42 (NR) | NR | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 16 | De Maria 2020 31 | Cross‐sectional | Italy | NR | 95 (NR) | NR | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 17 | Dell'Era 2020 32 | Cross‐sectional | Italy | 10–30 March 2020 | 355 (163) | 50.0 (40.0–59.5) | RT‐PCR | Subjective | In person interview or telephone questionnaire survey |
| 18 | Durrani 2020 33 | Cross‐sectional | Pakistan | 20 March–10 April 2020 | 30 (6) | 44.0 (7.0–81.0) | RT‐PCR | Subjective | Self‐reported |
| 19 | Freni 2020 34 | Cross‐sectional | Italy | NR | 50 (20) | 37.7 ± 17.9 | RT‐PCR | Subjective | Online questionnaire survey |
| 20 | Gelardi 2020 35 | Cross‐sectional | Italy | NR | 72 (33) | 49.7 (19.0–70.0) | RT‐PCR | Subjective | Self‐reported |
| 21 | Giacomelli 2020 4 | Cross‐sectional | Italy | 19 March 2020 | 59 (19) | 60.0 (50.0–74.0) | NR | Subjective | Self‐reported questionnaire survey |
| 22 | Gorzkowski 2020 36 | Cross‐sectional | France | 1 March–31 March 2020 | 229 (147) | 39.7 ± 13.7 | RT‐PCR | Subjective | Telephone questionnaire survey |
| 23 | Güner 2020 37 | Cross‐sectional | Turkey | 10 March–10 April 2020 | 222 (90) | 50.6 ± 16.5 | RT‐PCR | Subjective | Self‐reported |
| 24 | Haehner 2020 38 | Cross‐sectional | Germany | NR | 34 (16) | 43.2 ± 11.6 | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 25 | Hintschih 2020 39 | Cross‐sectional | Germany | NR | 41 (28) | 37 (NR) | RT‐PCR | Subjective | Online questionnaire survey |
| 26 | Hornuss 2020 40 | Cross‐sectional | Germany | April 2020 | 45 (20) | 56.0 ± 16.9 | RT‐PCR | Objective | Sniffin' Sticks test |
| 27 | Jalessi 2020 41 | Cross‐sectional | Iran | February–March 2020 | 92 (30) | 52.9 ± 13.2 | RT‐PCR | Subjective | Self‐reported |
| 28 | Karadaş 2020 42 | Cross‐sectional | Turkey | April–May 2020 | 239 (106) | 46.4 ± 15.4 | RT‐PCR | Subjective | Self‐reported |
| 29 | Kerr 2020 43 | Cross‐sectional | Ireland | 24 March 2020 | 46 (27) | 36.5 (27.0–48.0) | RT‐PCR | Subjective | Self‐reported |
| 30 | Kim 2020 44 | Cross‐sectional | Korea | 12–16 March 2020 | 172 (106) | 26.0 (22.0–47.0) | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 31 | Klopfenstein 2020 45 | Cross‐sectional | France | 1–17 March 2020 | 114 (36) | 47.0 ± 16.0) | RT‐PCR | NR | NR |
| 32 | Lapostolle 2020 46 | Cross‐sectional | France | 24 March–6 April 2020 | 1487 (752) | 44.0 (32.0–57.0) | RT‐PCR | Subjective | Telephone interview |
| 33 | Lazar 2020 47 | Cross‐sectional | Romania | 28 March 2020 | 100 (49) | 41.0 (NR) | RT‐PCR | Subjective | Medical record review |
| 34 | Lechien 2020 48 | Cross‐sectional | France, Italy, Spain, Belgium, and Switzerland | 22 March–10 April 2020 | 1420 (962) | 39.0 ± 12.0 | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 35 | Lechien 2020a 49 | Cross‐sectional | Belgium | NR | 86 (56) | 41.7 ± 11.8 | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 36 | Lechien 2020b 50 | Cross‐sectional | European countries | 22 March–3 June 2020 | 2581 (1624) | 44.5 ± 16.4 | RT‐PCR | Subjective | Self‐reported |
| 37 | Lechien 2020c 51 | Cross‐sectional | Belgium, Italy, France, and Spain | NR | 417 (263) | 36.9 ± 11.4 | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 38 | Lee 2020 52 | Cross‐sectional | Canada | 16 March–15 April 2020 | 56 (33) | 38.0 (31.8–47.2) | RT‐PCR | Subjective | Telephone questionnaire survey |
| 39 | Levinson 2020 53 | Cross‐sectional | Israel | 10–23 March 2020 | 42 (19) | 34.0 (15.0–82.0) | RT‐PCR | Subjective | Telephone questionnaire survey |
| 40 | Liang 2020 54 | Cross‐sectional | China | 16 March–12 April 2020 | 86 (42) | 25.5 (6.0–57.0) | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 41 | Lombardi 2020 55 | Cross‐sectional | Italy | 24 February–31 March 2020 | 139 (82) | NR | RT‐PCR | Subjective | Self‐reported |
| 42 | Luers 2020 56 | Cross‐sectional | Germany | 22–28 March 2020 | 72 (31) | 38.0 ± 13.0 | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 43 | Luigetti 2020 57 | Cross‐sectional | Italy | 14 March–20 April 2020 | 213 (76) | 70.2 ± 13.9 | RT‐PCR | Subjective | Self‐reported |
| 44 | Magnavita 2020 58 | Cross‐sectional | Italy | 27 March–30 April 2020 | 82 (56) | NR | RT‐PCR | Subjective | Self‐reported questionnaire |
| 45 | Mao 2020 59 | Cross‐sectional | China | 16 January–19 February 2020 | 214 (127) | 52.7 ± 15.5 | RT‐PCR | NR | NR |
| 46 | Martin‐Sanz 2020 60 | Case control | Spain | 15 March–7 April 2020 | 215 (171) | 42.9 ± 0.6 | RT‐PCR | Objective | VAS |
| 47 | Meini 2020 61 | Cross‐sectional | Italy | April 2020 | 100 (40) | 65.0 ± 15.0 | RT‐PCR | Subjective | Telephone interview |
| 48 | Menni 2020 5 | Cross‐sectional | UK | 24–29 March 2020 | 579 (400) | 40.79 ± 11.84 | RT‐PCR | Subjective | Smartphone‐based App survey |
| 49 | Menni 2020a 62 | Cross‐sectional | UK | 24 March–21 April 2020 | 6452 (4638) | 41.2 ± 12.1 | RT‐PCR | Subjective | Smartphone‐based App survey |
| USA | 726 (567) | 44.6 ± 14.3 | |||||||
| 50 | Mercante 2020 63 | Cross‐sectional | Italy | 5–23 March 2020 | 204 (94) | 52.6 ± 14.4 | RT‐PCR | Subjective | Telephone questionnaire survey |
| 51 | Merza 2020 64 | Cross‐sectional | Iraq | 18 March–7 April 2020 | 15 (6) | 28.0 ± 16.4 | RT‐PCR | NR | NR |
| 52 | Moein 2020 65 | Case–control | Iran | 21–23 March 2020 | 60 (20) | 46.5 ± 12.1 | RT‐PCR | Objective | UPSIT |
| 53 | Noh 2020 66 | Cross‐sectional | Korea | NR | 199 (130) | 38.0 ± 13.1 | RT‐PCR | Subjective | In person interview |
| 54 | Otte 2020 67 | Cross‐sectional | Germany | NR | 50 (NR) | 43.2 (23.0–69.0) | RT‐PCR | Objective | Sniffin' sticks test |
| 55 | Paderno 2020 68 | Cross‐sectional | Italy | 27 March–1 April 2020 | 508 (223) | 55.0 ± 15.0 | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 56 | Parente‐Arias 2020 69 | Cross‐sectional | Spain | 3–24 March 2020 | 151 (98) | 55.2 (18.0–88.0) | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 57 | Patel 2020 70 | Cross‐sectional | UK | 1 March–1 April 2020 | 141 (58) | 45.6 (20.0–93.0) | RT‐PCR | Subjective | Telephone interview |
| 58 | Petrocelli 2020 71 | Cross‐sectional | Italy | 16 April–2 May 2020 | 300 (225) | 43.6 ± 12.2 | RT‐PCR | Objective | Olfactory threshold and identification test |
| 59 | Peyrony 2020 72 | Cross‐sectional | France | 9 March–4 April 2020 | 225 (150) | 62.0 (48.0–71.0) | RT‐PCR | Subjective | Self‐reported |
| 60 | Qiu 2020 73 | Cross‐sectional | China, France and Germany | 15 March–5 April 2020 | 394 (NR) | NR | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 61 | Romero‐Sánchez 2020 74 | Cross‐sectional | Spain | 1 March–1 April 2020 | 841 (368) | 66.4 ± 14.9 | RT‐PCR | Subjective | Medical record review |
| 62 | Sakalli 2020 75 | Cross‐sectional | Turkey | NR | 172 (88) | 37.8 ± 12.5 | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 63 | Sayin 2020 76 | Case–control | Turkey | NR | 64 (39) | 37.7 ± 11.3 | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 64 | Seo 2020 77 | Cross‐sectional | Korea | 28 April 2020 | 62 (NR) | NR | RT‐PCR | Objective | CC‐SIT |
| 65 | Sierpiński 2020 78 | Cross‐sectional | Poland | 17–18 April 2020 | 1942 (1169) | 50.0 (NR) | RT‐PCR | Subjective | Telephone interview |
| 66 | Song 2020 79 | Cross‐sectional | China | 27 January–10 March 2020 | 1172 (595) | 61.0 (48.0–68.0) | RT‐PCR | Subjective | Telephone interview |
| 67 | Speth 2020 80 | Cross‐sectional | Switzerland | 3 March–17 April 2020 | 103 (53) | 46.8 ± 15.9 | RT‐PCR | Subjective | Telephone interview |
| 68 | Tomlins 2020 81 | Cross‐sectional | UK | 10–30 March 2020 | 95 (35) | 75.0 (59.0–82.0) | RT‐PCR | NR | NR |
| 69 | Tostmann 2020 82 | Cross‐sectional | Netherlands | 10–30 March 2020 | 79 (NR) | NR | NR | Subjective | Self‐reported questionnaire survey |
| 70 | Trubiano 2020 83 | Cross‐sectional | Australia | 1–22 April 2020 | 28 (14) | 55.0 (46.0–63.5) | RT‐PCR | Subjective | Medical record review |
| 71 | Tudrej 2020 84 | Cross‐sectional | Switzerland | 24 March–14 April 2020 | 198 (NR) | NR | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 72 | Vacchiano 2020 85 | Cross‐sectional | Italy | NR | 108 (46) | 59.0 (18.0–83.0) | RT‐PCR | Subjective | Telephone questionnaire survey |
| 73 | Vaira 2020 86 | Cross‐sectional | Italy | 31 March–6 April 2020 | 72 (45) | 49.2 ± 13.7 | RT‐PCR | Objective | CCCRC |
| 74 | Vaira 2020a 87 | Cross‐sectional | Italy | 9–10 April 2020 | 33 (22) | 47.2 ± 10 | RT‐PCR | Objective | CCCRC |
| 75 | Vaira 2020b 88 | Cross‐sectional | Italy | NR | 345 (199) | 48.5 ± 12.8 (23–88) | RT‐PCR | Objective | CCCCRC |
| 76 | Wee 2020 89 | Cross‐sectional | Singapore | 26 March–10 April 2020 | 154 (NR) | NR | RT‐PCR | Subjective | Self‐reported questionnaire survey |
| 77 | Wi 2020 90 | Cross‐sectional | Korea | 15 April 2020 | 111 (57) | 41.3 ± 19.0 | RT‐PCR | Subjective | Medical record review |
| 78 | Yan 2020 91 | Cross‐sectional | USA | 3 March–8 April 2020 | 128 (67) | 53.5 (40.0–65.0) | RT‐PCR | Subjective | Self‐reported |
| 79 | Yan 2020a 92 | Cross‐sectional | Germany, USA, Bolivia and Venezuela | NR | 59 (29) | 18.0–79.0 | RT‐PCR | Subjective | Online questionnaire survey |
| 80 | Yan 2020b 93 | Cross‐sectional | USA | 9 March–29 April 2020 | 46 (NR) | NR | RT‐PCR | Subjective | Medical record review |
| 81 | Zayet 2020 94 | Cross‐sectional | France | 26 February–14 March 2020 | 70 (41) | 56.7 ± 19.3 | RT‐PCR | Subjective | Self‐reported questionnaire |
| 82 | Zayet 2020a 95 | Case–control | France | 30 March–3 April 2020 | 95 (79) | 39.8 ± 12.2 | RT‐PCR | Subjective | Medical record review |
| 83 | Zou 2020 96 | Cross‐sectional | China | 1 February–3 March 2020 | 81 (43) | 58.0 (50.0–68.5) | RT‐PCR | Subjective | Medical record review |
AAO‐HNS = American academy of otolaryngology–head and neck surgery; CC‐SIT = cross‐cultural smell identification test; CCCRC = Connecticut chemosensory clinical research center orthonasal olfaction test; IQR = interquartile range; NR = not reported; RT‐PCR = reverse transcription polymerase chain reaction; SD = standard deviation; UPSIT = University of Pennsylvania smell identification test; VAS = visual analog scale..