Table 1.
Characteristics of the included studies.
| Characteristics | Number of studies | Percentage of the included studies (%) |
|---|---|---|
| Country | ||
| China | 111 | 51.15 |
| USA | 21 | 9.68 |
| Italy | 20 | 9.22 |
| South Korea | 7 | 3.23 |
| Spain | 7 | 3.23 |
| Iran | 6 | 2.76 |
| Germany | 5 | 2.30 |
| France | 5 | 2.30 |
| Mexico | 5 | 2.30 |
| India | 4 | 1.84 |
| UK | 4 | 1.84 |
| Brazil | 3 | 1.38 |
| Congo | 2 | 0.92 |
| Kuwait | 2 | 0.92 |
| Saudi Arabia | 2 | 0.92 |
| Bangladesh | 1 | 0.46 |
| Bolivia | 1 | 0.46 |
| Bulgaria | 1 | 0.46 |
| Denmark | 1 | 0.46 |
| Greece | 1 | 0.46 |
| Ireland | 1 | 0.46 |
| Oman | 1 | 0.46 |
| Poland | 1 | 0.46 |
| Qatar | 1 | 0.46 |
| Switzerland | 1 | 0.46 |
| Turkey | 1 | 0.46 |
| Multicountriesa | 2 | 0.92 |
| Data source | ||
| Multicenters | 83 | 38.25 |
| Single center | 134 | 61.75 |
| Type of study | ||
| Case series | 123 | 56.68 |
| Retrospective cohort study | 71 | 32.72 |
| Prospective cohort study | 10 | 4.61 |
| Ambispective cohort study | 1 | 0.46 |
| Case–control study | 4 | 1.84 |
| Cross-sectional study | 8 | 3.69 |
| Type of comparisonsb | ||
| Severe vs. non-severe | 74 | 34.10 |
| Death vs. survival | 105 | 48.39 |
| ICU vs. non-ICU | 53 | 24.42 |
| ARDS vs. non-ARDS | 6 | 2.76 |
a
One was carried out in Europe, and the other was conducted in China, Europe, and North America.
b
Seventeen studies had two types of comparisons. Two studies had three types of comparisons.