Table 1. Main characteristics of included studies.
| Study | Study design | Country | Setting | Number of patients | Age group of patients | Gender (% male) | ICU (%) | Patients who were ventilated n (%) | Patients who died n (%) | Viral co-infections n (%) | Bacterial co-infection n (%) | Fungal co-infections n (%) | Risk of bias |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Arentz, 2020 [22] | Case series | USA | ICUa | 21 | Adults | 52 | 100 | 15 (71) | 11 (52) | 3 (14) | 1 (50) | 0 (0) | Medium |
| Barrasa, 2020 [23] | Case series | Spain | ICU | 48 | Adults | 56 | 100 | 45 (94) | 16 (33) | 0 (0) | 6 (13) | 0 (0) | Low |
| Campochiaro, 2020 [24] | Prospective cohort | Italy | ICU and non-ICU | 65 | Adults | 29 | 6 | 25 (38) | 16 (25) | 0 (0) | 1 (2) | 0 (0) | Low |
| Chen, 2020 [25] | Case series | China | ICU | 99 | Adults | 68 | 100 | 17 (17) | 11 (11) | 0 (0) | 1 (1) | 4 (4) | Medium |
| Cuadrado-Payán, 2020 [26] | Case series | Spain | ICU | 4 | Adults | 75 | 75 | 3 (75) | 0 (0) | 4 (100) | 0 (0) | 0 (0) | High |
| Ding, 2020 [27] | Case series | China | Non-ICU | 115 | Adults | NRb | 0 | 0 (0) | 0 (0) | 5 (4) | 0 (0) | 0 (0) | Medium |
| Dong, 2020 [28] | Case series | China | Non-ICU | 11 | Adults/children | 54 | 0 | 1 (9) | 0 (0) | 1 (9) | 0 (0) | 0 (0) | Medium |
| Du, 2020 [29] | Case series | China | ICU | 109 | Adults | 67.9 | 48.6 | 33 (30) | 109 (100) | 0 (0) | NR | NR | Low |
| Fan, 2020 [30] | Retrospective cohort | China | ICU and non-ICU | 50 | Adults | 83 | 54 | 23 (46) | 12 (24) | 0 (0) | 5 (10) | 5 (10) | Low |
| Feng, 2020 [31] | Case series | China | ICU and non-ICU | 476 | Adults | 56.9 | 26 | 70 (15) | 38 (8) | 0 (0) | 35 (7) | 0 (0) | Medium |
| Garazzino, 2020 [32] | Retrospective cohort | Italy | ICU and non-ICU | 168 | Children | 55.9 | 1.1 | 2 (1) | 0 (0) | 10 (6) | 1 (0.5) | 0 (0) | Low |
| Gayam, 2020 [33] | Case series | USA | ICU and non-ICU | 350 | Adults | 33 | NR | NR | NR | 0 (0) | 1 (0.3) | 0 (0) | Medium |
| Huang, 2020 [34] | Case series | China | ICU and non-ICU | 41 | Adults | 73 | 32 | 4 (10) | 6 (15) | 0 (0) | 1 (2) | 0 (0) | Medium |
| Kakuya, 2020 [35] | Case series | Japan | Non-ICU | 3 | Children | 100 | 0 (0) | 0 (0) | 0 (0) | 1 (33) | 0 (0) | 0 (0) | Low |
| Khodamoradi, 2020 [36] | Case series | Iran | Non-ICU | 4 | Adults | 75 | 0 | 0 (0) | 0 (0) | 4 (100) | 0 (0) | 0 (0) | Medium |
| Kim, 2020 [37] | Retrospective cohort | USA | Non-ICU | 115 | Adults/children | 45 | 0 | 0 (0) | 0 (0) | 25 (22) | 0 (0) | 0 (0) | Low |
| Koehler, 2020 [38] | Case series | Germany | ICU | 19 | Adults | NR | 100 | NR | 3 (16) | 2 (11) | 0 (0) | 5 (26) | Medium |
| Lian, 2020 [39] | Retrospective cohort | China | ICU and non-ICU | 788 | Children/Adults | 52 | 3 | 18 (2) | 0 (0) | NR | 0 (0) | 0 (0) | Low |
| Lin, 2020 [8] | Case series | China | ICU and non-ICU | 92 | Adults | NR | NR | NR | NR | 6 (7) | NR | NR | Medium |
| Liu, 2020 [40] | Retrospective cohort | China | ICU and non-ICU | 12 | Children/Adults | 66 | NR | 6 (50) | NR | 0 (0) | 2 (17) | 0 (0) | Low |
| Lv, 2020 [41] | Retrospective cohort | China | ICU and non-ICU | 354 | Adults | 49 | NR | NR | 11 (3) | 1 (0.3) | 32 (9) | 6 (2) | Low |
| Ma, 2020 [42] | Retrospective cohort | China | NR | 93 | Adults | 55 | NR | NR | 44 (47) | 46 (49) | 0 (0) | 0 (0) | Low |
| Mannheim, 2020 [43] | Case series | USA | ICU and non-ICU | 64 | Children | 56 | 11 | NR | 0 (0) | 3 (5) | 1 (2) | 0 (0) | Medium |
| Mo, 2020 [44] | Case series | China | ICU and non-ICU | 155 | Adults | 55 | NR | 36 (23) | 22 (14) | 13 (8) | 2 (1) | 0 (0) | Medium |
| Nowak, 2020 [9] | Case series | USA | ICU and non-ICU | 1204 | Adults | 56 | NR | NR | NR | 36 (3) | 0 (0) | 0 (0) | Medium |
| Ozaras, 2020 [45] | Case series | Turkey | ICU and non-ICU | 1103 | Adults | 50 | NR | NR | NR | 6 (0.5) | 0 (0) | 0 (0) | Medium |
| Palmieri, 2020 [46] | Retrospective cohort | Italy | ICU and non-ICU | 3032 | Children/Adults | 67 | NR | NR | 3032 (100) | NR | NR | NR | Low |
| Peng, 2020 [47] | Retrospective cohort | China | ICU and non-ICU | 75 | Children | 58 | NR | NR | 0 (0) | 8 (11) | 31 (41) | 0 (0) | Low |
| Pongpirul, 2020 [48] | Case series | Thailand | ICU and non-ICU | 11 | Adults | 54 | NR | 0 (0) | 0 (0) | 2 (18) | 5 (45) | 0 (0) | Low |
| Richardson, 2020 [49] | Case series | USA | ICU and non-ICU | 5700 | Adults | 60 | 14.2 | 1151 (20) | 553 (10) | 39 (0.7) | 3 (0.1) | 0 (0) | Low |
| Sun, 2020 [50] | Retrospective cohort | China | ICU and non-ICU | 36 | Children | 61 | NR | NR | 1 (3) | 1 (3) | 1 (3) | 0 (0) | Medium |
| Tagarro, 2020 [51] | Retrospective cohort | Spain | ICU and non-ICU | 41 | Children | 44 | 9.7 | 4 (10) | 0 (0) | 2 (5) | 0 (0) | 0 (0) | Low |
| Wan, 2020 [52] | Case series | China | ICU and non-ICU | 135 | Adults | 53 | NR | 28 (21) | 1 (0.7) | NR | NR | NR | Medium |
| Wang Y, 2020 [53] | Case series | China | ICU and non-ICU | 55 | Adults | 40 | 0 | 0 (0) | 0 (0) | 1 (2) | 1 (2) | 1 (3) | Low |
| Wang L, 2020 [54] | Case series | China | ICU and non-ICU | 339 | Adults | 49 | NR | NR | 65 (19) | 0 (0) | 1 (0.3) | 1 (0.3) | Low |
| Wang R, 2020 [55] | Case series | China | ICU and non-ICU | 125 | Adults | 56.8 | 15.2 | 4 | 0 (0) | 1 (0.8) | 9 (7) | 9 (7) | Medium |
| Wang Y, 2020 [56] | Clinical trial | China | ICU and non-ICU | 237 | Adults | 56 | NR | 21 (9) | 14 (6) | NR | NR | NR | Medium |
| Wee, 2020 [57] | Prospective cohort | Singapore | ICU and non-ICU | 3807 | Adults | NR | NR | NR | 1 (0.02) | 3 (0.08) | NR | NR | Medium |
| Wu C, 2020 [58] | Retrospective cohort | China | ICU and non-ICU | 201 | Adults | 63.7 | 26.4 | 67 (33) | 44 (22) | 1 (0.5) | 0 (0) | 0 (0) | Low |
| Xia, 2020 [59] | Case series | China | ICU and non-ICU | 20 | pediatric | 65 | NR | 0 (0) | 0 (0) | 4 (0.2) | 1 (5) | 1 (5) | Medium |
| Yang X, 2020 [60] | Case series | China | ICU | 710 | Adults | 67 | 100 | 37 (5) | 32 (4) | 0 (0) | 4 (0.6) | 4 (0.6) | Low |
| Yi, 2020 [61] | Case series | USA | ICU and non-ICU | 132 | Adult | 62 | 50 | 5 (4) | 1 (0.8) | NR | NR | NR | Medium |
| Zhang J, 2020 [62] | Case series | China | ICU and non-ICU | 140 | Adults | 50.7 | NR | NR | NR | 2 (1) | 1 (0.7) | 1 (0.7) | Medium |
| Zhang G, 2020 [63] | Case series | China | ICU and non-ICU | 221 | Adults | 48.9 | 80 | 26 (12) | 5 (2) | 2 (0.9) | 6 (3) | 6 (3) | Medium |
| Zhao, 2020 [64] | Case series | China | ICU and non-ICU | 34 | Adults | 57.9 | 0 | 0 (0) | 0 (0) | 1 (3) | 1 (3) | 0 (0) | Medium |
| Zheng, 2020 [65] | Case series | China | ICU and non-ICU | 1001 | Adult and pediatric | NR | NR | NR | NR | 2 (0.2) | NR | NR | Low |
| Zhou, 2020 [66] | Retrospective cohort | China | ICU and non-ICU | 191 | Adult | 62 | 26 | 32 (17) | 54 (28) | NR | NR | NR | Low |
| Zhu, 2020 [67] | Retrospective cohort | China | ICU and non-ICU | 257 | Adult and pediatric | 53.7 | 1.16 | 0 (0) | 0 (0) | 9 (3) | 11 (4) | 11 (4) | Low |
| Alvares P, 2020 [68] | Retrospective cohort | Brazil | ICU and non-ICU | 32 | Pediatric | 59.3 | 9.3 | 2 (6) | 1 (3) | 1 (3) | NR | NR | Medium |
| Borman, 2020 [69] | Case series | UK | ICU | 719 | Adults | NR | 100.0 | NR | NR | NR | NR | 3NR | Low |
| Chauhdary W, 2020 [70] | Case series | Brunei Darussalam | ICU and non-ICU | 141 | Adults | NR | NR | NR | NR | 7 (5) | NR | Low | |
| Cheng L, 2020 [71] | Retrospective cohort | Hong Kong | ICU and non-ICU | 147 | Adults | 85.0 | 3.0 | NR | NR | NR | 4 (3) | NR | Low |
| Cheng Y, 2020 [72] | Retrospective cohort | China | ICU and non-ICU | 213 | Adults | 50.2 | 2 (1) | 8 (4) | 97 (46) | NR | NR | Low | |
| Cheng K, 2020 [73] | Retrospective cohort | China | NR | 212 | Adults/Children | 51.0 | 19 (9) | NR | NR | 13 (6) | NR | Low | |
| Contou D, 2020 [74] | Retrospective cohort | France | ICU | 92 | Adults | 79.0 | 100.0 | 83 (90) | 45 (49) | NR | 32 (35) | NR | Low |
| Dupont D, 2020 [75] | Case series | France | ICU | 19 | Adults | 78.0 | 100.0 | 18 (95) | NR | NR | NR | 19 (100) | Low |
| Elabbadi A, 2020 [76] | Case series | France | ICU | 101 | Adults | 78.2 | 100.0 | 83 (82) | 21 (21) | NR | 10 (10) | NR | Low |
| Falces-Romero, 2020 [77] | Retrospective cohort | Spain | ICU and non-ICU | 10 | Adults | 80.0 | 70.0 | 7 (70) | 7 (70) | NR | 0 | 10 (100) | Medium |
| Falcone M, 2020 [78] | Prospective cohort | Italy | ICU and non-ICU | 315 | Adults | 66.6 | 26.9 | 55 (17) | 70 (22) | NR | 11 (3) | 2 (1) | Medium |
| Fu Y, 2020 [79] | Case series | China | ICU and non-ICU | 5 | Adults | 80.0 | 100.0 | 5 (100) | NR | NR | 5 (100) | 2 (40) | Low |
| Garcia-Menino, 2021 [80] | Case series | Spain | ICU | 7 | Adults | 86.0 | 100.0 | NR | 1 (14) | NR | 7 (100) | NR | Low |
| Garcia-Vidal, 2021 [81] | Prospective cohort | Spain | ICU and non-ICU | 989 | Adults | 55.8 | 15.0 | NR | 103 (10) | 6 (1) | 47 (5) | 7 (1) | Low |
| Gouzien, 2020 [82] | Retrospective cohort | France | ICU | 53 | Adults | 67.9 | 100.0 | 53 (100) | 39 (74) | NR | NR | 1 (2) | Medium |
| Hashemi S, 2020 [83] | Case series | Iran | ICU and non-ICU | 105 | Adults/Children | NR | NR | 105 (100) | NR | NR | NR | Low | |
| Hazra A, 2020 [84] | Retrospective cohort | USA | ICU and non-ICU | 459 | NR | NR | NR | NR | 6 (1) | NR | NR | High | |
| He Bing, 2020 [85] | Retrospective cohort | China | NR | 21 | Adults/Children | NR | NR | 0 | NR | 2 (10) | 4 (19) | Medium | |
| Hirotsu Y, 2020 [86] | Prospective cohort | Japan | non-ICU | 191 | NR | NR | NR | NR | 32 (17) | NR | NR | Medium | |
| Hughes, 2020 [87] | Case series | UK | ICU | 836 | Adults | 62.0 | NR | 262 (31) | NR | 5 (1) | 27 (3) | Low | |
| Karaba, 2020 [88] | Retrospective cohort | USA | ICU and non-ICU | 1016 | Adults | 54.0 | 12.0 | NR | NR | 2 NR | 1NR | NR | Low |
| Kolenda, 2020 [89] | Prospective cohort | France | ICU | 99 | NR | NR | 100.0 | NR | NR | NR | 17 (17) | NR | Low |
| Kumar, 2021 [90] | Retrospective cohort | USA | ICU and non-ICU | 1573 | Adults | 57.9 | 31.0 | 247 (16) | 413 (26) | NR | 48 (3) | 9 (1) | Low |
| Lardaro T, 2020 [91] | Retrospective cohort | USA | ICU and non-ICU | 542 | Adults | 49.6 | 15.9 | 159 (29) | 78 (14) | NR | 8 (1) | NR | Medium |
| Lehmann C, 2020 [92] | Retrospective cohort | USA | ICU and non-ICU | 321 | Adults | 48.0 | 5.0 | NR | 22 (7) | 5 (2) | 7 (2) | NR | Medium |
| Lendorf, 2020 [93] | Retrospective cohort | Denmark | ICU and non-ICU | 115 | Adults/Children | 60.0 | 18.0 | 12 (10) | 16 (14) | NR | 9 (8) | 1 (1) | Medium |
| Li J, 2020 [94] | Retrospective cohort | China | ICU and non-ICU | 102 | Adults/Children | 66.7 | NR | 50 (49) | NR | 159 (156) | NR | Medium | |
| Li Z, 2020 [95] | Retrospective cohort | China | ICU and non-ICU | 32 | Adults | 62.5 | 40.0 | 6 (19) | NR | 6 (19) | 10 (31) | 2 (6) | High |
| Ma L, 2020 [96] | Retrospective cohort | China | ICU and non-ICU | 250 | Adults | 46.0 | 5 (2) | 4 (2) | 4 (2) | 2 (1) | NR | Low | |
| Mahmoudi H, 2020 [97] | Cross-sectional study | Iran | ICU and non-ICU | 342 | Adults | NR | NR | NR | NR | 6 (2) | NR | Medium | |
| Mendes N, 2020 [98] | Retrospective cohort | USA | ICU and non-ICU | 242 | Adults | 50.8 | 54 (22) | 52 (21) | NR | 6 (2) | NR | Low | |
| Mughal, 2020 [99] | Restrospective cohort | USA | ICU and non-ICU | 129 | Adults | 62.8 | 30.2 | 30 (23) | 20 (16) | NR | NR | NR | Low |
| Nasir N, 2020 [100] | Retrospective cohort | Pakistan | ICU and non-ICU | 30 | Adults | 83.0 | 33.0 | 24 (80) | 7 (23) | NR | 6 (20) | 7 (23) | Low |
| Nasir N, 2020 [101] | Retrospective cohort | Pakistan | ICU and non-ICU | 147 | Adults | 60.0 | NR | NR | 9 (6) | 1 (1) | Medium | ||
| Ng K F, 2020 [102] | Case series | China | ICU and non-ICU | 8 | Pediatric | 25.0 | 25.0 | NR | NR | 5 (63) | NR | NR | Low |
| Nori, 2021 [103] | Retrospective cohort | USA | ICU and non-ICU | 152 | Adults/Children | 59.0 | 55.9 | NR | 86 (57) | NR | 112 (74) | 3 (2) | Low |
| Obata, 2020 [104] | Retrospective cohort | USA | ICU and non-ICU | 226 | Adults | 55.1 | 24.8 | NR | 41 (18) | NR | 8 (4) | 8 (4) | Medium |
| Oliva, 2020 [105] | Case series | Italy | ICU and non-ICU | 7 | Adults | 57.0 | 14.3 | NR | NR | NR | 7 (100) | NR | Low |
| Papamanoli, 2020 [106] | Retrospective cohort | USA | ICU and non-ICU | 447 | Adults | 66.0 | 45.2 | 115 (26) | 102 (23) | NR | NR | NR | Low |
| Peci A, 2021 [107] | Case-control | Canada | ICU and non-ICU | 325 | Adults/Children | NR | NR | NR | 8 (2) | NR | NR | Low | |
| Pereira, 2021 [108] | Case-control | New York | ICU and non-ICU | 87 | Adults | 60.9 | 48.3 | NR | 32 (37) | 10 (11) | 6 (7) | 1 (1) | Medium |
| Pettit, 2020 [109] | Retrospective cohort | USA | ICU and non-ICU | 148 | Adults | 37.5 | 70.3 | 48 (32) | 46 (31) | 1 (1) | 14 (9) | 2 (1) | Low |
| Pickens, 2021 [110] | Retrospective cohort | Chicago | ICU | 179 | Adults | 61.5 | 100.0 | 179 (100) | 34 (19) | NR | 28 (16) | NR | Low |
| Ramadan H, 2021 [111] | Prospective cohort | Egypt | ICU and non-ICU | 260 | Adults | 55.4 | 8 (3) | 24 (9) | NR | 37 (14) | NR | Low | |
| Reig S, 2020 [112] | Retrospective cohort | Germany | ICU and non-ICU | 213 | Adults | 61.0 | 33.0 | 57 (27) | 51 (24) | NR | 26 (12) | 6 (3) | Low |
| Ripa M, 2020 [113] | Prospective cohort | Italy | ICU and non-ICU | 731 | Adults | 68.0 | 12.0 | NR | 194 (27) | NR | 24 (3) | 11 (2) | Low |
| Rothe K, 2020 [114] | Retrospective cohort | Germany | ICU and non-ICU | 140 | Adults | 64.0 | 15.0 | 41 (29) | NR | NR | NR | 9 (6) | Low |
| Segrelles-Calvo G, 2021 [115] | Case series | Spain | ICU and non-ICU | 7 | Adults | 71.0 | 86.0 | 7 (100) | 5 (71) | NR | NR | 7 (100) | Low |
| Sharifipour E, 2020 [116] | Prospective cohort | Iran | ICU | 19 | Adults | 58.0 | 100.0 | 19 (100) | 18 (95) | NR | 19 (100) | NR | Low |
| Sogaard, 2021 [117] | Retrospective cohort | Switzerland | ICU and non-ICU | 162 | Adults | 61.1 | 25.3 | NR | 17 (10) | 5 (3) | 19 (12) | 3 (2) | Low |
| Soriano, 2021 [118] | Retrospective cohort | Spain | ICU | 83 | Adults | 79.0 | 100.0 | 78 (94) | 20 (24) | NR | 7 (8) | NR | Low |
| Tang, 2021 [119] | Retrospective cohort | China | NR | 78 | Adults/Children | 53.0 | NR | NR | 4 (5) | 5 (6) | NR | Low | |
| Torrego, 2020 [120] | Retrospective cohort | Spain | ICU | 163 | NR | NR | 100.0 | 139 (85) | 23 (14) | NR | 18 (11) | NR | High |
| Townsend, 2020 [121] | Prospective cohort | Ireland | ICU and non-ICU | 117 | Adults | 63.0 | 29.1 | NR | 17 (15) | NR | 6 (5) | 1 (1) | Low |
| Verroken, 2020 [122] | Prospective cohort | Belgium | ICU | 32 | NR | NR | 100.0 | NR | NR | NR | 13 (41) | NR | Medium |
| Wang L, 2020 [123] | Retrospective cohort | UK | ICU and non-ICU | 1396 | Adults | 65.0 | 30.0 | NR | 420 (30) | NR | 11 (1) | NR | Low |
| Wei L, 2020 [124] | Retrospective cohort | China | non-ICU | 43 | Adults | 0.0 | 0.0 | NR | NR | 15 (35) | NR | NR | Low |
| White P, 2020 [125] | Retrospective cohort | UK | ICU and non-ICU | 135 | Adults | 69.0 | NR | 51 (38) | NR | NR | 36 (27) | Low | |
| Wu Q, 2020 [126] | Retrospective cohort | China | NR | 74 | Pediatric | 59.5 | 1 (1) | NR | 10 (14) | 16 (22) | NR | Low | |
| Xia P, 2020 [127] | Retrospective cohort | China | ICU | 81 | Adults | 66.7 | 100.0 | 66 (81) | 60 (74) | NR | 34 (42) | NR | Low |
| Xu J, 2020 [128] | Retrospective cohort | China | ICU | 239 | Adults | 59.8 | 100.0 | 165 (69) | 147 (62) | NR | 25 (10) | NR | Low |
| Xu S, 2020 [129] | Retrospective cohort | China | ICU and non-ICU | 64 | Adults | 0.0 | 1.6 | NR | NR | 9 (14) | 10 (16) | NR | Low |
| Xu W, 2021 [130] | Retrospective cohort | China | ICU and non-ICU | 659 | Adults/Children | 50.4 | 5.0 | NR | NR | NR | 48 (7) | NR | Low |
| Yao T, 2020 [131] | Retrospective cohort | China | NR | 83 | Adults | 63.9 | 71 (86) | 83 (100) | NR | 36 (43) | NR | Low | |
| Yu C, 2020 [132] | Retrospective cohort | China | NR | 128 | Adults | 43.0 | NR | 14 (11) | 64 (50) | 5 (4) | NR | Low | |
| Yue H, 2020 [133] | Retrospective cohort | China | NR | 307 | Adults | 47.3 | NR | NR | 176 (57) | NR | NR | Medium | |
| Yusuf E, 2021 [134] | Case-control | Netherlands | ICU | 92 | Adults | 76.1 | 100.0 | NR | NR | NR | NR | 10 (11) | High |
| Zhang C, 2020 [135] | Retrospective cohort | China | NR | 34 | Pediatric | 41.0 | NR | NR | 13 (38) | 9 (26) | NR | Low | |
| Zhang H, 2020 [136] | Retrospective cohort | China | NR | 38 | Adults | 84.2 | 23 (61) | 8 (21) | NR | 37 (97) | 3 (8) | Low |
aICU: intensive care unit.
bNR: Not reported.