1. STANDARDIZED INFECTION RATIO SIMPLIFIED
Laurie Fish, RN, BSN, CIC

2. Standardized Infection Ratio
The SIR is a summary measure used to compare the HAI experience among one or more groups of patients to that of a standard population.
Groups can be in various units of measure (unit, hospital, state or country)
The data in the group is aggregated into a summary measure and then compared to the standard population

3. Definition of SIR
The number of observed infections in an index group divided by the number of infections expected in that group, based on a standard population.
Observed (O) HAIs
Expected (E) HAIs
This is the number of HAIs in your hospital
= SIR
This is the estimated number for your hospital based on standard population

4. Standard Population Standard Population for CAUTI is 2009
Standard Population for CLABSI is
Standard Population for CAUTI is 2009
4/17/2017

5. How does my facilities performance compare?
What is the relative difference in HAI occurrence between my facility compared to a common benchmark or referent period (standard population)
This is the question the SIR answers for us.
4/17/2017

6. Making Comparisons
Standard population
Index group (your facility)
Your actual (observed) number is then divided by your expected= SIR
Your expected is determined using the following formula:
standard population rate/1000 X your device days= Expected

7. How is the CLABSI SIR calculated?
The national rate of CLABSI for a teaching medical surgical unit is 2.1/1000 cath days
Hospital A Data:
Org id
Location
Summary Yr/Half
Months
Infcount
Number expected
Central line days
SIR
SIR P Value
95% Confidence Interval
10018
ICU
2009H1 3 2
1.785
850
1.12
0.5327
The E for ICU = (2.1/1000) X 850 = 1.75
SIR = 2/1.785 = 1.12

8. Expected less than 1
If the expected is less that 1, a SIR will not be calculated.
If the expected is less than 1 your denominator is too low to calculate a precise SIR

9. How is SIR Calculated at hospital level?
Type of ICU
# of CLABSI
# of central line days
CLABSI Rate
NHSN Rate
p value
Expected # of CLABSI
Medical Cardiac 2
380
5.26
2.0
0.09
0.76
Medical 1
257
3.89
2.6
0.15
0.67
Med/Surgical 3
627
4.78
1.5
0.11
0.94
Neurosurgical
712
2.81
2.5
0.32
1.78
Total 8
1976
4.05
4.15
Overall CLABSI SIR= Observed/Expected= 8/4.15=1.93

10. Interpretation of the SIR
During the first 6 months of 2012, there was 1 CLABSI identified in our facility and we observed 2945 catheter days.
Based on the data we expected CLABSIs
This results in a SIR of (almost 80% better than expected)
The p value and 95% confidence interval indicates the number of observed is not significantly lower that expected.

11. Interpretation of statistical tests
Tip: The expected is one so it is significant if this range does not contain 1.
p value: <0.05 is considered statistically significant
Confidence Interval: if the range between the 2 numbers does not contain 1 the value is considered statistically significant.
SIR Value of 1

12. Risk Adjustment: CLABSI and CAUTI
Population level risk adjustment:
Patient mix by type of unit location
Hospital affiliation with a medical school
Bed size for the patient care location

13. Risk Adjustment for Surgical Site Infection
Includes only deep and organ space and are detected through readmission to the same hospital
Colon: Age, ASA, duration, endoscope, medical school affiliation, bed size, wound class
Abdominal hysterectomy: Age, ASA, duration of procedure, hospital bed size

14. The SIR is not….
“The SIR is NOT intended as a comprehensive and conclusive HAI measure for all users and users of HAI data.”
“More specific data at the state and local level are needed to target specific HAI problems and monitor the impact of prevention programs.”
4/17/2017

15. Questions?