Table 2.
Summary of included studies
| Study authors | Covid-19 patient population size (n) | Patients with olfactory dysfunction | Study location | Study type | Oxford level of evidence | NHI-SQAT score |
|---|---|---|---|---|---|---|
| Aggarwal et al.16 | 16 | 3 (19%) subjective olfactory &/or taste dysfunction | Des Moines, USA | Retrospective cohort study | 4 | Fair |
| Beltrán-Corbellini et al.17 | 79 | 25 (31.65%) subjective olfactory dysfunction | Madrid, Spain | Case series | 4 | Fair |
| Carignan et al.18 | 134 | 87 (64.9%) subjective olfactory &/or taste dysfunction | Quebec Eastern Townships, Canada | Retrospective cohort study | 4 | Fair |
| Giacomelli et al.19 | 59 | 20 (33.9%) subjective olfactory &/or taste dysfunction | Milan, Italy | Cross-sectional study | 4 | Fair |
| Hornuss et al.20 | 45 | 38 (84%) objective olfactory dysfunction | Freiburg, Germany | Cross-sectional study | 4 | Good |
| Kai Chua et al.21 | 31 | 7 (22.6%) subjective olfactory dysfunction | Singapore | Cross-sectional study | 4 | Fair |
| Kim et al.22 | 213 | 68 (31.9%) subjective olfactory dysfunction | Seoul, South Korea | Cross-sectional study | 4 | Good |
| Klopfenstein et al.23 | 114 | 54 (47.4%) subjective olfactory dysfunction | Trévenans, France | Retrospective cohort study | 4 | Fair |
| Lechien et al.24 | 417 | 357 (85.6%) subjective olfactory dysfunction, with validated tool | 12 European hospitals | Cross-sectional study | 4 | Good |
| Lechien et al.25 | 2013; subset of 93 patients were eligible for objective olfactory evaluation | 1754 (87%) subjective olfactory dysfunction | 18 European hospitals | Cross-sectional study | 4 | Good |
| Lechien et al.26 | 86 | 53 (62%) objective olfactory dysfunction | Mons, Belgium | Cross-sectional study | 4 | Good |
| Lechien et al.27 | 1420 | 70.2% subjective olfactory dysfunction | 18 European hospitals | Cross-sectional study | 4 | Fair |
| Lee et al.28 | 3191 | 488 (15.3%) subjective mixed olfactory &/or taste dysfunction in patients at early stage of Covid-19 | Daegu, South Korea | Cross-sectional study | 4 | Good |
| Li et al.29 | 145 | 16 (11%) objective olfactory dysfunction 25 days from symptom onset | Wuhan, China | Cross-sectional study | 4 | |
| Luers et al.30 | 72 | 53 (73.61%) subjective dysfunction | Cologne, Germany | Retrospective cohort study | 4 | Fair |
| Menni et al.31 | 6452 in UK, 726 in USA | 64.8% in UK & 67.5% in USA had subjective olfactory &/or taste dysfunction | UK & USA | Cross-sectional study | 4 | Good |
| Moein et al.32 | 60 | 59 (98.33%) objective olfactory dysfunction, 21 (35%) subjective olfactory &/or taste dysfunction | Teheran, Iran | Case series | 4 | Fair |
| Noh et al.33 | 199 | 52 (26.1%) subjective olfactory dysfunction | Gyeongju, Republic of Korea | Cross-sectional study | 4 | Good |
| Ottaviano et al.34 | 6 | 6 (100%) objective olfactory dysfunction | Padova, Italy | Case series | 4 | Fair |
| Paderno et al.35 | 508 (295 hospitalised + 213 home-quarantined) | 44% in hospitalised group & 72% in home-quarantined group had subjective olfactory dysfunction | Brescia, Italy | Cross-sectional study | 4 | Good |
| Speth et al.36 | 103 | 61.2% subjective olfactory dysfunction | Aarau, Switzerland | Cross-sectional study | 4 | Good |
| Spinato et al.37 | 202 | 130 (64.36%) subjective mixed olfactory &/or taste dysfunction | Treviso, Italy | Cross-sectional study | 4 | Fair |
| Tostmann et al.38 | 79 | 37 (46.8%) subjective olfactory dysfunction | Nijmegen, Netherlands | Cross-sectional study | 4 | Fair |
| Trubiano et al.39 | 28 | 11 (39.3%) subjective mixed olfactory &/or taste dysfunction | Melbourne, Australia | Retrospective cohort study | 4 | Fair |
| Tsivgoulis et al.40 | 22 | 16 (72.7%) objective olfactory dysfunction | Athens, Greece | Cross-sectional study | 4 | Good |
| Vaira et al.41 | 345 | 256 (74.2%) subjective chemosensitive disorders, but 30.1% of 89 patients who did not report dysfunction proved objectively hyposmic | Sassari, Salerno, Milan & Bologna, Italy | Cross-sectional study | 4 | Good |
| Vaira et al.42 | 72 | 60 (83.33%) objective dysfunction; 44 (61.1%) subjective dysfunction | Sassari, Italy | Case series | 4 | Good |
| Vaira et al.43 | 33 | 25 (75.76%) had dysfunction on objective & self-administered test; 17 (51.52%) had subjective dysfunction | Sassari, Bologna & Salerno, Italy | Cross-sectional study | 4 | Fair |
| Wee et al.44 | 154 | 22.7% subjective mixed olfactory &/or taste dysfunction | Singapore | Cross-sectional study | 4 | Poor |
| Yan et al.2 | 59 | 40 (67.8%) subjective dysfunction | La Jolla, USA | Cross-sectional study | 4 | Good |
| Yan et al.45 | 128 | 75 (58.59%) subjective dysfunction | La Jolla, USA | Cross-sectional study | 4 | Good |
| Zayet et al.46 | 95 | 60 (63.2%) dysfunction | Trévenans, France | Retrospective cohort study | 4 | Good |
Covid-19 = coronavirus disease 2019; NHI-SQAT = National Heart, Lung, and Blood Institute Study Quality Assessment Tools