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Table 2 Classification of departments in terms of frequency of surgeries, and univariate analysis of risk and confounding factors of SSI

From: Association between the frequency of surgeries for video-assisted thoracic surgery and the incidence of consequent surgical site infections: a retrospective observational study based on national surveillance data

   Department groups in terms of average number of all kinds of procedures/year Univariate analysis against
    Department group SSI
total < 50/year 50–100/year > 100/year p value p value
Department, N 74 38 16 20   
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%)   
  1. NNIS National Nosocomial Infections Surveillance System, SSI surgical site infections