13-0300 edwards nhsn metrics analysis day2 workshop2
TRANSCRIPT
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American Recovery and Reinvestment Act
Epidemiology and Laboratory Capacity (ELC)for Infectious Disease Program
Healthcare-Associated Infections (HAIs)
rantee eet ng
October 19-20, 2009
Jonathan R. Edwards, M.Stat
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NHSN HAI Com arison Metrics
. ,Statistics Team Leader, DHQP
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ec ves
Review HAI point estimation
Describe improved SIR calculations
Discuss options for hospital comparisons
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Point Estimation for
HAI Surveillance
A type of statistical inference often
Turn surveillance data into decision
Allows you to express surveillance
Numerator
DenominatorX Constant
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e C S ate ab e
Exam le CLABSI Rate Table
Local CLABSI Rates Aggregate CLABSI Ratep-values for local vs. aggregate
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ropor on
within the denominator
Numerator is the magnitude of the partDenominator is the magnitude of the whole
Often expressed as a percent
Surgical site infection rate:
280 women undergoing hysterectomyX 100 = 1.4%
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Local SSI Rates Aggregate SSI Ratep-va ue or oca vs. aggrega e
Percenti le rank amon all hos itals
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Standardized
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t t
an ar ze n ec on a o
Standardized Infection Ratio, SIR, is asummary measure used to compare the
HAI experience among one or more groups
o pa en s o a o a s an ar popu a on s(e.g. NHSN)
n rec s an ar za on me o
Accounts for differences in risk of HAIamong the groups
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a cu a ng an
Observed (O) HAIsExpected (E) HAIs
To calculate O, sum the number of HAIs among agroup
o ca cu a e , requ res e use o e appropr a e
aggregate data (risk-adjusted rates)
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oo s ream
Infections
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d a ds J et a J ect Co t o 609 6
nnua epor
Edwards JR et al. Am J Infect Control 2008 36:609-26.
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d a ds J et a J ect Co t o 609 6
nnua epor
Edwards JR et al. Am J Infect Control 2008 36:609-26.
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xamp e a e a e
Type of # # Central CLABS NHSN p-value
Location CLABSI line-da s I Rate
Rate
Coronary 2 380 5.26 2.1 0.09
Cardiothoracic 1 257 3.89 1.4 0.15
Medical 3 627 4.78 2.4 0.11
Med/Surg, 2 712 2.81 2.0 0.32
major teachingo a . --- ---
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xamp e a e a e
Type of # # Central CLABS NHSN p-value Expected
Location CLABSI line-days I Rate # of
a e
Coronary 2 380 5.26 2.1 0.09 0.8
. . .
Medical 3 627 4.78 2.4 0.11
, . . .
major teaching
Total 8 1976 4.05 --- ---
Expected Number = 380 * (2.1 / 1000) = 380 * 0.0021 = 0.8
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xamp e a e a e
Type of # # Central CLABS NHSN p-value Expected
Location CLABSI line-days I Rate # of
a e
Coronary 2 380 5.26 2.1 0.09 0.80
. . . .
Medical 3 627 4.78 2.4 0.11 1.15
, . . . .
major teaching
Total 8 1976 4.05 --- --- 3.73
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p
xamp e a e a e
Type of # # Central CLABS NHSN p-value Expected
Location CLABSI line-days I Rate # of
a e
Coronary 2 380 5.26 2.1 0.09 0.80
. . . .
Medical 3 627 4.78 2.4 0.11 1.15
, . . . .
major teaching
Total 8 1976 4.05 --- --- 3.73
Observed
8
Standardized Infection Ratio SIR ==
= 2.14xpec e .
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External Comparison of an SIR tou .
SIR = 1.0 Observed Number of SSI
= Expected Number of SSI
Is the SIR of Hosp A (2.14) significantly greater than 1.0?
Answer: p-value = 0.07 (Poisson test)
,
"significantly greater" than expected
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Sur ical Site
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Edwards JR et al. Am J Infect Control 2008;36:609-26.
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Annual NHSN Re ort
Edwards JR et al. Am J Infect Control 2008;36:609-26.
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xamp e a e a e
Procedure Index # # SSI NHSN p-value
SSI procedures Rate Rate
Cardiac surgery 0,1
2,3
3
3
80
20
3.75
15.0
2.02
5.29
0.25
0.08
CBGB 0 1 10 10.0 1.59 0.16
1
2,3
10
5
230
60
4.35
8.33
3.15
5.76
0.20
0.28o a . --- ---
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xamp e a e a e
Procedure Index # # SSI NHSN p-value Expected
SSI procedures Rate Rate # of SSI
Cardiac surgery 0,1
2,3
3
3
80
20
3.75
15.0
2.02
5.29
0.25
0.08
1.6
CBGB 0 1 10 10.0 1.59 0.16
1
2,3
10
5
230
60
4.35
8.33
3.15
5.76
0.20
0.28o a . --- ---
Expected Number = 80 * (2.02 / 100) = 80 * 0.0202 = 1.6
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xamp e a e a e
Procedure Index # # SSI NHSN p-value Expected
SSI procedures Rate Rate # of SSI
Cardiac surgery 0,1
2,3
3
3
80
20
3.75
15.0
2.02
5.29
0.25
0.08
1.6
1.1
CBGB 0 1 10 10.0 1.59 0.16 0.2
1
2,3
10
5
230
60
4.35
8.33
3.15
5.76
0.20
0.28
7.2
3.5. --- --- .
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xamp e a e a e
Procedure Index # # SSI NHSN p-value Expected
SSI procedures Rate Rate # of SSI
,
2,3 3 20
.
15.0
.
5.29
.
0.08
.
1.1
CBGB 0 1 10 10.0 1.59 0.16 0.2
1
2,3
10
5
230
60
4.35
8.33
3.15
5.76
0.20
0.28
7.2
3.5
Total 22 400 5.50 --- --- 13.6
Observed
22
Standardized Infection Ratio (SIR) =
=
= 1.62
.
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Standardized Infection Ratio (SIR)
Ratio of Observed to Expectedinfections
Risk-adjusted summary measure
any two patient cohorts, groups, orhospitals
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"significantly greater" than expected
an SIR to its Nominal Value of 1.0
SIR = 1.0 Observed Number of SSI
=
Is the SIR of Team A (1.62) significantly greater than
1.0?
- = .
,
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on ence n erva or
3
21
ZO
99 = OOEL
3
111 ++
+
+
=
EOSIR
U
2Z
Example normal curve values
90% confidence
z = 1.645.95% confidencez.025 = 1.96
99% confidence
z.005 = 2.58
Liddell FDK. JECH 1984;38:85-89.
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-Comparing Surgical Site Infections
Skip
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Incisional SSI after CSEC
Factor Parameter Estimate OR p-valueIntercept -6.300 - -
Body Mass 0.046 1.047
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t
og s c egress on o e
General formula
= + + + +
Where:
p
pro a y o a er opera on intercept
1, 2 , 3 ...
X1, X2 , X3 ... risk factors
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= =
Logistic Model
Factor Parameter Estimate
Intercept -6.300
o y ass .
Duration of labor > 9 hr 0.506
ASA > 3 0.598
Reciprocal age (years) 14.961
logit (p) = + 1 X1+ 2 X2 + 3 X3 + 4 X4
= -6.300 + 0.046 (Body Mass) +
*
+
0.598 ASA
3* +14.961 ( 1 / Age)
* = =,
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Risk Factors
= Duration of labor = 12 hours
ASA score = 1=
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Lo istic Model
Calculation for Example Patient #1
lo it =
+ X + X + X + X
logit( ) = -6.300 + 0.046 (28) + 0.506 (1) +p
. . = - .
= logit ( ) + logit ( ) p p
= e -3.825 / (1 + e -3.825)= 0.022 or 2.2% riskp
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Risk Factors
Duration of labor = 9 hours
ASA score = 3
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Lo istic Model
Calculation for Example Patient #2
lo it =
+ X + X + X + X
logit ( ) = -6.300 + 0.046 (36) + 0.506 (1) +
p
. . = - .
= logit ( ) + logit ( ) p p
= e -2.708 / (1 + e -2.708)= 0.063 or 6.3% riskp
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= =
Incisional SSI after CSEC
BodyDuration
Patient Mass of labor ASA Age SSI p1 28 12 1 22 0 0.0222 36 9 3 18 1 0.063
.
. . . . . . .
. . . . . . .
. . . . . . .
100 31 8 4 38 0 0.020.
SIR = O/E = 3 / 2.3 = 1.3
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n erpre ng an
If SIR = 1, or O = E, observed SSIs equalsthe expected SSIs based on NHSN
If SIR is significantly >1, this suggests the
for the contributing procedures
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onc us ons
Appropriate multivariate models are useful toe er es ma e rs
Calculation of a risk-adjusted StandardizedInfection Ratio (SIR) will improve
compar sons or osp a s
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osp a s ompare o
Hospital SIR p-value Status
A 1.2 0.12 Same
. . ameC 2.7 0.001 High
D 0.7 0.002 Low
. .
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osp a roups
I)
2
%C
R(9
re erence ne
SI
0
HospitalsA B C D E F G H I
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t t
o u e o cases
xac m s
a
tio
fection
rdized
I
S
tand
Volume of cases
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as resen osp a s
Hospital Past Present Status
A 1.2 1.6 Same
B 0.9 0.8 SameC 2.7 1.9 Lower
D 0.7 1.1 HigherE 1.5 1.2 Lower
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Thank You