Table 2 Classification of departments in terms of frequency of surgeries, and univariate analysis of risk and confounding factors of SSI
| Â | Â | Department groups in terms of average number of all kinds of procedures/year | Univariate analysis against | |||
|---|---|---|---|---|---|---|
| Â | Â | Â | Department group | SSI | ||
total | < 50/year | 50–100/year | > 100/year | p value | p value | |
Department, N | 74 | 38 | 16 | 20 | Â | Â |
Department characteristics | ||||||
 Mean of number of beds | 409.5 | 315 | 449.4 | 557 | < 0.0001 |  |
 Number of teaching hospitals | 4 | 0 | 0 | 4 | 0.0012 |  |
 Number of tertiary hospitals | 21 | 5 | 6 | 10 | 0.0074 |  |
 Number of cancer centers | 3 | 0 | 1 | 2 | 0.11 |  |
Thoracic surgery | ||||||
 Total number (from 2014 to 2018) | 26,878 | 3086 | 5718 | 18,074 |  |  |
 Number of surgical site infections | 335 | 43 | 60 | 232 |  |  |
 Rate of surgical site infections (%) | 1.25 | 1.39 | 1.05 | 1.28 |  |  |
 Median number of procedures / year | 72.6 | 11.8 | 68.6 | 145.2 |  |  |
Open thoracic surgery | ||||||
 Procedures | 5724 | 841 | 1051 | 3832 |  |  |
 Number of surgical site infections | 100 | 10 | 25 | 65 |  |  |
 Rate of surgical site infections (%) | 1.75 | 1.12 | 2.38 | 1.7 |  |  |
Video-assisted thoracic surgery (VATS) |  |  |  |  | < 0.0001 | 0.0001 |
 Procedures | 21,154 | 2245 | 4667 | 14,242 |  |  |
 Number of surgical site infections | 235 | 33 | 35 | 167 |  |  |
 Rate of surgical site infections (%) | 1.11 | 1.47 | 0.75 | 1.17 |  |  |
Age (median, IQR) | 68 (55–74) | 63 (27–73) | 68 (57–75) | 68 (59–74) | < 0.0001 | 0.06 |
Sex |  |  |  |  | < 0.0001 | < 0.0001 |
 Female | 7345 (34.7%) | 582 (25.9%) | 1575 (33.7%) | 5188 (36.4%) |  |  |
 Male | 13,809 (65.3%) | 1663 (74.1%) | 3092 (66.3%) | 9054 (63.6%) |  |  |
Emergency operation |  |  |  |  | < 0.0001 | 0.605 |
 Yes | 1187 (5.6%) | 264 (11.8%) | 152 (3.3%) | 771 (5.4%) |  |  |
 No | 19,967 (94.4%) | 1981 (88.2%) | 4515 (96.7%) | 13,471 (94.6%) |  |  |
NNIS risk index |  |  |  |  | < 0.0001 | < 0.0001 |
 0 | 14,160 (66.9%) | 1601 (71.3%) | 2415 (51.7%) | 10,144 (71.2%) |  |  |
 1 | 6343 (30.0%) | 565 (25.2%) | 2001 (42.9%) | 3777 (26.5%) |  |  |
 2,3 | 651 (3.1%) | 78 (3.5%) | 251 (5.4%) | 321 (2.3%) |  |  |