Table 5.
Results of the primary and secondary outcomes and sensitivity analyses
| Outcome, n (%)a | Unadjusted | Adjustedb | ||
|---|---|---|---|---|
| Anaemia (n = 6324) | Infection (n = 12,930) | OR (95% CI) | p-value | |
| Primary outcomes | ||||
| Blood transfusion | 183 (2.9) | 302 (2.3) | 0.83 (0.36, 1.91) | 0.67 |
| Deep SSI (MSSA) (PHE) | 8 (0.13) | 18 (0.14) | 1.01 (0.42, 2.46) | 0.98 |
| Secondary infection outcomes | ||||
| Deep SSI (MSSA) (CDC) | 8 (0.13) | 18 (0.14) | 1.01 (0.42, 2.46) | 0.98 |
| Deep SSI (MSSA) (either) | 8 (0.13) | 18 (0.14) | 1.01 (0.42, 2.46) | 0.98 |
| Deep SSI (any) (PHE) | 23 (0.36) | 48 (0.37) | 0.97 (0.57, 1.64) | 0.91 |
| Deep SSI (any) (CDC) | 23 (0.36) | 48 (0.37) | 0.97 (0.57, 1.64) | 0.91 |
| Deep SSI (any) (either) | 23 (0.36) | 48 (0.37) | 0.97 (0.57, 1.64) | 0.91 |
| Superficial SSI (MSSA) (PHE) | 5 (0.08) | 4 (0.03) | 0.49 (0.13, 1.86) | 0.29 |
| Superficial SSI (MSSA) (CDC) | 5 (0.08) | 10 (0.08) | 0.93 (0.25, 3.45) | 0.91 |
| Superficial SSI (MSSA) (either) | 5 (0.08) | 10 (0.08) | 0.93 (0.25, 3.45) | 0.91 |
| Superficial SSI (any) (PHE) | 16 (0.25) | 33 (0.26) | 1.11 (0.55, 2.25) | 0.77 |
| Superficial SSI (any) (CDC) | 18 (0.28) | 48 (0.37) | 1.30 (0.62, 2.73) | 0.49 |
| Superficial SSI (any) (either) | 18 (0.28) | 48 (0.37) | 1.30 (0.62, 2.73) | 0.49 |
| Secondary outcomes | ||||
| n= 6138 | n= 9911 | |||
| Unplanned readmissions | 390 (6.4) | 464 (4.7) | 1.09 (0.54, 2.19) | 0.81 |
| n= 6324 | n= 12,693 | |||
| Critical care admission | 182 (2.9) | 465 (3.7) | 1.05 (0.46, 2.43) | 0.90 |
| IRR(95%CI) | p-value | |||
| Length of stay on critical carec,d | ||||
| N, mean (SD) | 182, 1.7 (1.4) | 465, 1.5 (1.3) | 1.05 (0.79, 1.41) | 0.73 |
| Median (min, max) | 1 (0, 12) | 1 (0, 17) | ||
| N, mean (SD) | 6324, 0.05 (0.4) | 12,693, 0.06 (0.4) | 0.97 (0.86, 1.09) | 0.56 |
| Median (min, max) | 0 (0, 12) | 0 (0, 17) | ||
| n= 6138 | n= 9911 | |||
| Length of hospital stayc | ||||
| Mean (SD) | 183 (3.9) | 184 (3.1) | 1.03 (0.93, 1.14) | 0.53 |
| Median (min, max) | 3 (0, 137) | 3 (0, 91) | ||
| Sensitivity analyses | OR(95%CI) | |||
| Excluding contaminated sites | n=6324 | n=8607 | ||
| Blood transfusion | 138 (2.9) | 230 (2.7) | 0.81 (0.36, 1.84) | 0.62 |
| Deep SSI (MSSA) (PHE) | 8 (0.13) | 14 (0.16) | 1.28 (0.52, 3.16) | 0.59 |
| Ischaemic heart disease as covariate | n=6138 | n=12,295 | ||
| Blood transfusion | 176 (2.9) | 265 (2.2) | 0.83 (0.37, 1.86) | 0.65 |
| Excluding sites with no transfusions | n=6243 | n=11,965 | ||
| Blood transfusion | 183 (2.9) | 302 (2.5) | 1.03 (0.52, 2.05) | 0.94 |
| Excluding sites with no reported infections | n=6243 | n=11,712 | ||
| Deep SSI (MSSA) (PHE) | 8 (0.13) | 18 (0.15) | 1.28 (0.51, 3.24) | 0.60 |
| Excluding sites with 100% infection confirmation | n=5162 | n=11,903 | ||
| Deep SSI (MSSA) (PHE) | 6 (0.12) | 14 (0.12) | 0.85 (0.31, 2.37) | 0.76 |
Deep infections measured up to 90 days post-surgery; superficial infections measured up to 30 days post-surgery; unplanned readmission within 30 days of discharge; critical care admissions, and time spent on critical care, up to 30 days post-surgery
SSI surgical site infection, MSSA methicillin-susceptible Staphylococcus aureus, PHE Public Health England, CDC Centre for Disease Control, OR odds ratio, IRR incidence rate ratio
aUnless mean (SD), median, minimum, maximum as stated
bTreatment effects associated with infection arm presented
cMidnights in hospital
dFirst analysis includes only those admitted to critical care, second also includes those not admitted to critical care imputing 0 midnights in critical care and using a zero-inflated model