Table 1. Summary of descriptive statistics for included studies.
| Characteristic | Number | Percentage of total |
|---|---|---|
| Publication type | ||
| Pre-print | 27 | 44% |
| Peer-reviewed | 34 | 56% |
| Study design | ||
| Case control | 26 | 43% |
| Cohort | 22 | 36% |
| Case series | 7 | 11% |
| Basic science study | 3 | 5% |
| Narrative review | 1 | 2% |
| Systematic review with meta-analysis | 1 | 2% |
| Non-randomised clinical trial | 1 | 2% |
| Study population | ||
| Human | 58 | 95% |
| Animal | 2 | 3% |
| Both | 1 | 2% |
| Country from which study population was drawn | ||
| China | 32 | 52% |
| Europe excl. UK (France, Germany, Italy, Spain, Sweden, Netherlands) | 13 | 21% |
| USA | 3 | 5% |
| UK | 3 | 5% |
| Other countries | 6 | 11% |
| Multiple populations | 2 | 3% |
| N/A (lab or animal based) | 2 | 3% |
| Sampling context | ||
| Hospital | 50 | 82% |
| Mixed hospital and community | 1 | 2% |
| Community | 6 | 10% |
| Laboratory (animal) | 2 | 3% |
| N/A (review) | 2 | 3% |