13-0300 edwards nhsn metrics analysis day2 workshop2

8/10/2019 13-0300 Edwards NHSN Metrics Analysis Day2 Workshop2

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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



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



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



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



,

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

13-0300 edwards nhsn metrics analysis day2 workshop2

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