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Letter
SARS Epidemiology Modeling
(Replies)
Ying-Hen Hsieh,*
Jen-Yu Lee,* and Hsiao-Ling Chang†
*National Chung Hsing University, Taichung, Taiwan, and †Department of
Health, Taipei, Taiwan
Appendix (Online Only)
| Appendix
Table 1. Study 1, patient characteristics, methicillin-resistant
Staphylococcus aureus (MRSA), controls not infected with S.
aureus and controls with methicillin-susceptible S. aureus
(MSSA) surgical site infections, bivariable analyses |
|
|
Variable
|
Cases, MRSA (%)
(n = 121)
|
Controls, uninfected patients (%)
(n = 193)
|
p value, (MRSA vs. uninfected controls)
|
Controls, MSSA (%)
(n = 165)
|
p value (MRSA vs. MSSA)
|
|
|
Age, mean ± SD, y
|
63.9 ± 15.4
|
57.3 ± 18.3
|
0.001
|
55.1 ± 17.4
|
<0.001
|
|
Male sex
|
55 (45.5)
|
92 (42.7)
|
0.73
|
90 (54.6)
|
0.15
|
|
Coexisting conditions
|
|
Diabetes mellitus
|
59 (48.8)
|
66 (34.2)
|
0.01
|
57 (34.6)
|
0.02
|
|
Hematologic disorder
|
1 (0.8)
|
1 (0.5)
|
1.00
|
2 (1.2)
|
1.00
|
|
HIV infection
|
0 (0.0)
|
1 (0.5)
|
1.00
|
0
|
1.00
|
|
Hypertension
|
64 (52.9)
|
75 (38.9)
|
0.02
|
80 (48.5)
|
0.48
|
|
Liver disease
|
4 (3.3)
|
1 (0.5)
|
0.07
|
2 (1.2)
|
0.25
|
|
Malignancy
|
15 (12.4)
|
14 (7.3)
|
0.16
|
13 (7.9)
|
0.23
|
|
Obesity
|
10 (8.3)
|
12 (6.2)
|
0.50
|
18 (10.9)
|
0.55
|
|
Peripheral vascular
disease
|
12 (9.9)
|
3 (1.6)
|
0.002
|
9 (5.5)
|
0.17
|
|
Pulmonary disease
|
21 (17.4)
|
23 (11.9)
|
0.19
|
32 (19.4)
|
0.76
|
|
Renal disease
|
19 (15.7)
|
9 (4.7)
|
0.002
|
13 (7.9)
|
0.06
|
|
Transplant
|
1 (0.8)
|
0
|
0.39
|
0
|
0.42
|
|
Tobacco use
|
16 (13.2)
|
20 (10.4)
|
0.47
|
24 (14.6)
|
0.86
|
|
Alcohol abuse
|
4 (3.3)
|
2 (1.0)
|
0.21
|
6 (3.6)
|
1.00
|
|
Hospital-related risk factors
|
|
Treatment at the
academic tertiary
care hospital
|
94 (77.8)
|
125 (64.8)
|
0.02
|
109 (66.1)
|
0.04
|
|
LOS before surgery,
median, IQR
|
1, 0–4
|
0, 0–3
|
0.02
|
0, 0–2
|
0.01
|
|
LOS before culture,
median, IQR
|
8, 5–14
|
NA
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NA
|
5, 3–10
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<0.001
|
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Proportion of patients
with an ICU stay
before surgery
|
11 (9.1)
|
13 (7.9)
|
0.83
|
18 (9.3)
|
1.0
|
|
ASA score, median,
IQR
|
3, 3–4
|
3, 2–4
|
0.03
|
3, 2–4
|
0.15
|
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Duration of surgery
(min), median, IQR
|
240, 166–305
|
194, 113–276
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0.004
|
202, 116–285
|
0.01
|
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Wound class,
median, IQR
|
1, 1–1
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1, 1–1
|
0.82
|
1, 1–1
|
0.36
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NNIS Risk Index,
median, IQR
|
1, 1–2
|
1, 1–1
|
0.002
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1, 1–2
|
0.06
|
|
| aLOS, length of
stay; IQR, interquartile range; ASA, American Society of Anesthesiologists-Physical
Status score; NNIS, National Nosocomial Infections Surveillance System. |
| Appendix
Table 2. Study 1: Adjusted outcomes models for methicillin-resistant
Staphylococcus aureus (MRSA) surgical site infection (SSI)
compared to uninfected control patientsa |
|
|
Variable
|
Deaths
|
Length of stayb
|
Costc
|
|
OR (95% CI)
|
ORd (95% CI)
|
OR (95% CI)
|
|
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MRSA
|
11.4 (2.8 to 34.9)
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3.2 (2.7 to 3.7)
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2.2 (2.0 to 2.6)
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ASA scoree,f
|
|
1.3 (1.2 to 1.5)
|
ASA score = 4
3.7 (1.5 to 8.9)
|
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ASA score = 2
2.0 (1.4 to 2.9)
|
|
ASA score = 3
3.0 (2.1 to 4.3)
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ASA Score = 4
4.1 (2.8 to 6.0)
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>73 y of age
|
4.8 (2.0 to 11.6)
|
|
|
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Operative duration (min)g
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211–400
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|
(0.9 to 1.3)
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1.4 (1.2 to 1.7)
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401–590
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1.7 (1.2 to 2.4)
|
2.2 (1.6 to 3.1)
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>590
|
1.8 (1.1 to 2.9)
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2.6 (1.6 to 4.0)
|
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Length of stay before surgeryh
|
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7–13 d
|
|
1.6 (1.1 to 2.1)
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1.7 (1.3 to 2.3)
|
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14–20 d
|
3.6 (1.4 to 9.6)
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5.6 (2.3 to 13.4)
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>20 d
|
0.7 (0.2 to 2.6)
|
1.2 (0.3 to 4.3)
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Intensive care unit stay before surgery
|
|
1.5 (1.2 to 2.0)
|
|
Tertiary care hospital
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1.5 (1.2 to 1.7)
|
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| aOR, odds ratio;
CI, confidence interval; ASA, American Society of Anesthesiologists
-Physical Status. |
| bModel includes
the following confounding variables: admission to the tertiary care
hospital, diabetes, and renal disease. |
| cModel includes
the following confounding variable: renal disease. |
| dFor length of
hospital stay and cost, OR represents multiplicative effect |
| eLength of stay
increases by 1.3-fold for each point increase in ASA score. |
| fFor cost, reference
category is ASA score = 1. |
| gReference category
is operative duration < 211 min. |
| hReference category
is length of stay before surgery < 7 d. |
| Appendix Table
3. Study 1, adjusted outcomes models for methicillin-resistant
Staphylococcus. aureus (MRSA) surgical site infections (SSI)
compared to patients with methicillin-resistant S. aureus (MSSA)
SSIa |
|
| |
Deathsb
|
Length of Stayc
|
Costd
|
|
|
Variable
|
OR (95% CI)
|
OR (95% CI)e
|
ORe (95% CI)
|
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MRSA
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3.4 (1.5 to 7.7)
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1.2 (1.0 to 1.5)
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1.2 (1.0 to 1.4)
|
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ASA scoref
|
ASA score = 4
5.1 (2.1 to12.5)
|
ASA score = 2
0.9 (0.5 to 1.7)
|
ASA score = 2
1.0 (0.7 to 1.5)
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|
ASA score = 3
1.6 (0.9 to 2.9)
|
ASA score = 3
1.4 (1.0 to 2.1)
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Asa score = 4
1.8 (1.0 to 3.5)
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ASA score = 4
2.1 (1.4 to 3.2)
|
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Age > 61 years
|
3.0 (1.2 to 7.3)
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Operative duration, ming
|
|
|
|
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206–381
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1.3 (1.0 to 1.6)
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1.4 (1.1 to 1.6)
|
|
382–557
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1.3 (0.8 to 2.1)
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1.8 (1.3 to 2.5)
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>557
|
1.1 (0.5 to 2.6)
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1.6 (0.9 to 2.8)
|
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Length (d) of stay before infectionh
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|
|
|
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11–20
|
1.4 (1.0 to 1.8)
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1.6 (1.3 to 2.0)
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21–30
|
1.6 (1.0 to 2.7)
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1.7 (1.2 to 2.5)
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>30
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1.3 (0.5 to 3.1)
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1.8 (0.9 to 3.8)
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Renal disease
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|
1.5 (1.0 to 2.2)
|
|
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Length (d) of intensive care unit stay before infectioni
|
|
|
|
|
8–14
|
1.8 (1.1, 2.8)
|
|
15–21
|
2.1 (1.1, 8.8)
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>21
|
1.9 (0.4, 8.0)
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Tertiary care hospital
|
|
|
1.3 (1.1, 1.6)
|
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| aOR, odds ratio;
CI, confidence interval; ASA, American Society of Anesthesiologists
-Physical Status. |
| bModel includes
the following confounding variable: operative duration >222 min. |
| cModel includes
the following confounding variables: admission to tertiary care hospital
and diabetes. |
| dModel includes
the following confounding variables: diabetes and renal disease. |
| eFor length of
hospital stay and cost, OR represents multiplicative effect. |
| fFor deaths, reference
category is ASA score < 1; for length of stay and cost, reference
category is ASA score = 1. |
| gReference category
is operative duration < 206 min. |
| hReference category
is length of stay prior to infection < 11 d. |
| iReference category
is intensive care unit length of stay prior to infection < 8 d. |
| Appendix
Table 4. Study 2, patient characteristics, vancomycin-resistant
enterococci (VRE) wound infections, controls not infected with enterococci,
and controls with vancomycin-susceptible enterococci (VSE) wound infections,
bivariate analyses |
|
|
Variable
|
Cases, VRE wound (%)
(n = 99)
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Controls, not infected (%)
(n = 280)
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P Value
(VRE vs. controls not infected)
|
Controls, VSE (%) (n = 213)
|
p value
(VRE vs. VSE)
|
|
|
Age, mean (y)
|
60.3
|
63.6
|
0.09
|
59.1
|
0.51
|
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Sex (female)
|
46 (46)
|
124 (44.3)
|
0.7
|
127 (59.6)
|
0.03
|
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Main diagnosis
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Orthopedic condition
|
11 (11)
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30 (10.7)
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18 (8.4)
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Cardiovascular condition
|
25 (25)
|
117 (41)
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61 (28.6)
|
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Endocrine disorder
|
3 (3)
|
6 (2.1)
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|
4 (1.9)
|
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Gastrointestinal disorder
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25 (25)
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60 (21.4)
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62 (29.1)
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Genitourinary disorder
|
6 (6)
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12 (4.2)
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9 (4.3)
|
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Infectious disease
|
16 (16)
|
6 (2.1)
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20 (9.4)
|
|
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Hematologic disease
|
0 (0)
|
2 (.7)
|
|
0
|
|
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Neurologic disease
|
11 (11)
|
32 (11.4)
|
|
34 (16)
|
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Pulmonary disease
|
2 (2)
|
14 (5)
|
|
5 (2.4)
|
|
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Coexisting conditions
|
|
|
|
|
|
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Cardiovascular disease
|
73 (74)
|
204 (72.9)
|
0.86
|
150 (70.4)
|
0.55
|
|
Lung disease
|
11 (11)
|
33 (11.7)
|
0.9
|
26 (12.2)
|
0.78
|
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Diabetes mellitus
|
67 (67.7)
|
139 (49.6)
|
0.002
|
127 (59.6)
|
0.17
|
|
Organ transplant recipient
|
14 (14)
|
21 (7.5)
|
0.08
|
18 (8.4)
|
0.12
|
|
Renal disease
|
18 (18.2)
|
39 (14)
|
0.7
|
28 (13.2)
|
0.24
|
|
Malignancy
|
7 (7.1)
|
27 (9.6)
|
0.5
|
32 (15)
|
0.05
|
|
AIDS
|
2 (2)
|
2 (0.7)
|
0.27
|
0
|
0.1
|
|
Hepatobiliary disease
|
16 (16.6)
|
40 (14.3)
|
0.8
|
31 (14.5)
|
0.71
|
|
Charlson comorbidity score, mean
|
3.17
|
2.66
|
0.07
|
|
|
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Hospital-related risk factors
|
|
|
|
|
|
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Transfer from another
institution
|
34 (34.3)
|
102 (36.4)
|
0.5
|
34 (16)
|
<0.001
|
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Surgery
|
29 (29.3)
|
94 (33.6)
|
0.08
|
90 (42.3)
|
0.03
|
|
Admission to ICU
|
26 (26.2)
|
58 (20.7)
|
0.9
|
53 (33.3)
|
0.8
|
|
| Appendix
Table 5. Study 2, adjusted outcomes models for vancomycin-resistant
enterococcus (VRE) wound infection compared to uninfected control
patientsa |
|
|
Variable
|
Deathsb
|
Variable
|
Length of Stayc
|
Variable
|
Costd
|
|
|
|
|
OR (95% CI)
|
ORe (95% CI)
|
ORe (95% CI)
|
|
|
VRE infection
|
2.0 (0.8 to 5.2)
|
VRE infection
|
1.8 (1.3 to 2.4)
|
VRE infection
|
1.5 (1.3, 1.8)
|
| |
|
Transfer from another hospital
|
1.5 (1.2 to 1.9)
|
Surgerye
|
1.4 (1.1, 1.8)
|
| |
|
Renal disease
|
2.0 (1.5 to 2.7)
|
|
|
| |
|
Malignancy
|
0.7 (0.5 to 0.9)
|
|
|
| |
|
Intensive care unit stayf
|
2.3 (1.6 to 3.3)
|
|
|
|
| aOR, odds ratio; CI, confidence
interval. |
| bModel includes the following
confounding variables: intensive care unit (ICU) stay and number of
coexisting conditions. |
| cModel includes the following
confounding variable: propensity score (i.e., likelihood of being
a VRE case). |
| dModel includes the following
confounding variables: propensity score [i.e., likelihood of being
a VRE case (Appendix)] and length of stay before infection (index
date for controls). |
| eFor length of hospital stay
and cost, OR represents multiplicative effect. |
| fBefore infection for cases
and before index date for controls. |
| Appendix Table
6. Study 2, adjusted outcomes models for vancomycin-resistant
enterococcus (VRE) wound infection compared to control patients with
wound infection due to vancomycin-susceptible enterococcus (VSE)a |
|
|
Variable
|
Deathsb
|
Variable
|
Length of Stayc
|
Variable
|
Costd
|
|
|
|
|
Odds Ratio (OR)
(95% Confidence Interval [CI])
|
ORe (95% CI)
|
ORe (95% CI)
|
|
|
VRE
|
2.5 (1.1, 6.1)
|
VRE
|
1.1 (0.9, 1.4)
|
VRE
|
1.4 (1.2, 1.6)
|
|
Intensive care unit stay (ICU)f
|
9.0 (3.0, 27.4)
|
ICU stayf
|
1.8 (1.3, 2.5)
|
Surgeryf
|
1.2 (1.1, 1.3)
|
|
| aOR, odds ratio;
CI, confidence interval; ICU, intensive care unit. |
| bModel includes
the following confounding variables: gender and surgery before infection. |
| cModel includes
the following confounding variable: malignancy and length of stay
before infection. |
| dModel includes
the following confounding variables: length of stay before cohort
inclusion. |
| eFor length of
hospital stay and cost, OR represents multiplicative effect. |
| fBefore infection
for cases and before index date for controls. |
|
