Uppal S, Harris J, Al-Niami A, Swenson CW, Pearlman MK, Reynolds RK, et al. Prophylactic antibiotic choice and risk of surgical site infection after hysterectomy. Obstet Gynecol 2016;127.
The authors provided this information as a supplement to their article.
Copyright © 2016 American College of Obstetricians and Gynecologists. Page 1 of 6
Appendix 1. Propensity Score Matching Analysis
Method: We used propensity score matching to confirm the results of the multivariable logistic regression. Propensity score matching allows for comparisons between patients receiving a different treatment (antibiotic type) but having a similar surgical risk profile. The propensity score is the probability from 0 to 1 of each patient receiving a particular antibiotic regimen, given a set of known variables, and is used to reduce potential selection bias, confounding, and differences between treatment groups in observational studies.
The beta-lactam antibiotic group was considered as the reference group. Two separate propensity score matching analysis were performed (1. Beta-lactam vs. beta-lactam alternatives 2. Beta- lactam vs Non-standard). The propensity score–matching approach was accomplished in 2 steps.
First, the probability of receiving PCN allergy antibiotic regimen was modeled using multiple logistic regressions. From this regression, the propensity score for receiving this regimen was computed for each patient. Second, the beta-lactam alternative groups patients were matched 1:1 to patients in the beta-lactam group based on a k-nearest neighbor match algorithm with common support restriction. The first table below (“Beta-lactam Antibiotics Compared With Beta-lactam Alternative Group”) illustrates the unmatched and matched values with p-values for the two groups. Similarly, for the second propensity score model Non-standard regimen patients were matched to the beta-lactam antibiotics regimen (see the Table, “Propensity Score Matching:
Beta-lactam Antibiotics Compared With Nonstandard Antibiotics”).
Results:
Beta-lactam antibiotics vs. beta-lactam alternative group:
Uppal S, Harris J, Al-Niami A, Swenson CW, Pearlman MK, Reynolds RK, et al. Prophylactic antibiotic choice and risk of surgical site infection after hysterectomy. Obstet Gynecol 2016;127.
The authors provided this information as a supplement to their article.
Copyright © 2016 American College of Obstetricians and Gynecologists. Page 2 of 6
A total of 4,688 patients receiving beta-lactam antibiotic were matched to 2,857 receiving beta- lactam alternatives. (See the table, “Beta-lactam Antibiotics Compared With Beta-lactam Alternative Group.”) The overall rate of surgical site infection was noted to be 2.1% in the patients receiving beta-lactam antibiotics compared to 3.1% in those receiving beta-lactam alternatives (p=0.006).
Propensity score matching – Beta-lactam antibiotics vs non-standard antibiotics:
A total of 1,231 patients receiving beta-lactam antibiotics were matched to 649 patients receiving non-standard antibiotics. The overall rate of SSI was significantly higher in those receiving non- standard regimens (3.7% vs. 1.4%, p<0.001).
Uppal S, Harris J, Al-Niami A, Swenson CW, Pearlman MK, Reynolds RK, et al. Prophylactic antibiotic choice and risk of surgical site infection after hysterectomy. Obstet Gynecol 2016;127.
The authors provided this information as a supplement to their article.
Copyright © 2016 American College of Obstetricians and Gynecologists. Page 3 of 6
Beta-lactam Antibiotics Compared With Beta-lactam Alternative Group
Unmatched Matched
Beta-lactam antibiotics N = 17,827
Beta- lactam alternative
N = 2,878
p Beta-lactam antibiotics (N=4,688)
Beta- lactam alternative (N=2,857)
p
Age, mean (years) 48 48.5 0.033 48.6 48.5 0.449
Diabetes, % 8.2 10.6 <0.0001 10.6 10.5 0.932
ASA Category ≥3, % 20.4 25.9 <0.0001 25.7 25.9 0.868
BMI, mean (kg/m2) 30.8 31.3 <0.001 31.4 31.4 0.717
Coronary Artery Disease, % 2.4 3.5 0.002 3.6 3.5 0.803
Hypertension, % 2.9 3.2 0.001 3.3 3.2 0.440
Smoker, % 2.3 2.5 0.004 2.5 2.5 0.820
Surgery time, mean (hrs) 2.2 2.157 0.990 2.172 2.2 0.649
Total estimated blood loss, mean (ml)
25.9 26.9 <0.001 26.9 26.9 0.988
Uppal S, Harris J, Al-Niami A, Swenson CW, Pearlman MK, Reynolds RK, et al. Prophylactic antibiotic choice and risk of surgical site infection after hysterectomy. Obstet Gynecol 2016;127.
The authors provided this information as a supplement to their article.
Copyright © 2016 American College of Obstetricians and Gynecologists. Page 4 of 6
Total estimated blood loss, mean (ml)
175.3 176.3 0.826 174.4 176.4 0.773
Open Case, % 27.4 26.3 0.231 25.7 26.3 0.578
Malignancy, % 10.8 9.8 0.004 11.1 10.8 0.704
Outcomes
Any SSI, % 1.8 3.1 <0.001 2.1 3.1 0.006
Superficial SSI,% 0.9 1.4 0.012 1.1 1.4 0.13
Deep/Organ space SSI,% 0.9 1.6 0.001 1 1.6 0.03
PCN – Penicillin; SSI – Surgical site infection; BMI – Body mass index; ASA – American society of anesthesiology
Uppal S, Harris J, Al-Niami A, Swenson CW, Pearlman MK, Reynolds RK, et al. Prophylactic antibiotic choice and risk of surgical site infection after hysterectomy. Obstet Gynecol 2016;127.
The authors provided this information as a supplement to their article.
Copyright © 2016 American College of Obstetricians and Gynecologists. Page 5 of 6
Propensity Score Matching: Beta-lactam Antibiotics Compared With Nonstandard Antibiotics
Unmatched Matched
Beta-lactam antibiotics (N = 17,827)
Non- standard
(N = 653)
p Beta-lactam antibiotics (N=1,231)
Non-
standard (N =649)
p-value
Age, mean (years) 48 47.9 0.870 48 47.9 0.904
Diabetes, % 8.2 10.4 0.043 11.9 10.5 0.404
ASA Category, % 20.4 26 0.001 25 26.2 0.634
BMI, mean (kg/m2) 30.8 31.6 0.005 31.1 31.8 0.177
Coronary Artery Disease, %
2.5 4.3 0.004 5.2 4.3 0.435
Hypertension 0.294 0.320 0.155 0.297 0.319 0.400
Smoker 22.9 26.5 0.034 27.6 26.5 0.662
Surgery time (hrs) 2.2 2.1 0.006 2 2 0.974
Total relative value units, RVUs
25.9 25.4 0.350 25.2 2.4 0.771
Uppal S, Harris J, Al-Niami A, Swenson CW, Pearlman MK, Reynolds RK, et al. Prophylactic antibiotic choice and risk of surgical site infection after hysterectomy. Obstet Gynecol 2016;127.
The authors provided this information as a supplement to their article.
Copyright © 2016 American College of Obstetricians and Gynecologists. Page 6 of 6
Total estimated blood loss, mean (ml)
175.2 162.1 0.197 164.0 162.1 0.889
Open Case, % 27.4 24.5 0.106 23.5 24.5 0.673
Malignancy, % 9.1 9.7 0.639 9.6 9.6 0.962
Outcomes
Any SSI, % 1.8 3.7 <0.001 1.4 3.7 0.001
Superficial SSI,% 0.9 2.3 0.001 0.7 2.3 0.004
Deep/Organ space SSI,%
0.9 1.5 0.13 0.7 1.5 0.06
PCN – Penicillin; SSI – Surgical site infection; BMI – Body mass index; ASA – American society of anesthesiology
