Sir, could you explain the

SIR?Dana Burshell, MPH, CPH, CIC

Andrea Alvarez, MPHHealthcare-Associated Infections Program

Virginia Department of Health

June 2012

What is a standardized infection ratio?

The standardized infection ratio (SIR) is a summary measure used to track healthcare-associated infections (HAIs) at a national, state, or local level over time. The SIR adjusts for patients of varying risk within each facility.

- The National Healthcare Safety Network (NHSN)

The SIR calculation• In HAI data analysis, the SIR compares the actual

number of HAIs reported (observed) with the baseline U.S. experience (predicted) adjusting for several risk factors that have been found to be significantly associated with differences in infection incidence.

• SIR is a ratio that is a comparison of two values

SIR = number of observed HAIs number of predicted HAIs

What is the “baseline U.S. experience”?

• 2006-2008 NHSN aggregate data are used as the standard population and considered to be the baseline U.S. experience for the SIR calculations.

• NHSN baseline data used in an SIR are used to calculate the predicted number of HAIs adjusting for the identified risk factors.

What does the SIR number mean?• An SIR greater than 1.0 indicates that more HAIs were

observed than predicted. • An SIR of 1.0 indicates that the number of HAIs observed

was equal to the number predicted.• An SIR less than 1.0 indicates that fewer HAIs were

observed than predicted.

• However, the SIR alone does not imply statistical significance. – The SIR is only a point estimate and needs additional information

to indicate if the finding is significant and not likely due to chance (that is, statistically significantly different from 1).

Statistical significance• A p-value and 95% confidence interval (CI) are

calculated by NHSN for each SIR. • The p-value identifies if the information is

statistically significant. The 95% CI can sometimes be used to approximate statistical significance.– If the p-value is < 0.05, the SIR is “statistically

significant".– If the SIR 95% CI does not contain the value 1, the SIR is

considered "statistically significant".

How do I interpret the SIR?Facility name

CLABSI (#)

Central line days

(#)

Predicted CLABSIs

(#)

SIR SIR p-value

SIR 95% CI

Hospital X 8 1,976 4.15 1.93 0.06 0.83, 3.80

• During 2011, there were 8 CLABSIs identified and 1,976 central line days observed in Hospital X’s intensive care units.

• Based on the NHSN 2006-2008 baseline data and the composition of ICU locations in Hospital X, 4.15 CLABSIs were predicted.

• This results in an SIR of 1.93 (O/P= 8/4.15), signifying that during this time period, Hospital X identified 93% more CLABSIs than predicted.

• The p-value (0.06) and 95% confidence interval (CI) (0.83, 3.80) indicate that the number of observed CLABSIs is not statistically significantly higher than the number of predicted CLABSIs. (Reminder: If the p-value is not less than 0.05 and the 95% CI does crosses 1, the SIR is not statistically significantly different than 1.)

How is the SIR being used currently?

• NHSN SIR reports– CLABSI, SSI, CAUTI

• CMS Hospital Compare website– CLABSI

• Updated VDH HAI report– CLABSI

• Other states• Within hospitals

Benefits of using the SIR• Single metric

– One number that can be used to make comparisons• Scalable

– National, regional, facility-wide, location-specific, by surgeon for SSIs, etc.

– Can combine the SIR values at any level of aggregation – Can perform more detailed comparisons within any individual risk

group• Risk-adjusted

– Adjusts for factors known to be associated with differences in HAI rates– Risk-adjustment differs between types of HAIs and types of surgical

procedures

- HHS HAI Action Plan - http://www.hhs.gov/ash/initiatives/hai/appendices.html#appendix_g_comparison

Intra-facility data sharing benefits:

• Top benefits identified by SSI pilot study IPs (2011)– Increased awareness of HAIs within the facility– Presented data to those who can make a difference– Provided benchmark data to support improvement

initiatives– Kept HAIs in the spotlight

Sharing the SIR with hospital leadership: One IP’s experience

• Reasons IP decided to educate hospital staff:– Hospital Compare website was using the SIR– VDH had started using the SIR– Corporate 2011 report used SIR

• Important leadership staff members to educate:– Leadership in IP (Chairman, Chief Nursing personnel, Quality Director)

• Presentation included:– Explanation of SIR and example calculation – Hospital Compare screenshot– Examples of CLABSI corporate SIRs compared with CLABSI rates– Tables from VDH newsletter comparing CLABSI rates from 2009-11 next to

SIRs. – NHSN data summary reports to show where comparative data comes from

Presented data

• # infections• # CL days• SIR

• # predicted• p-value• 95% CI• Comparison

• National• State• Bedsize• Hospital

• Historical data

Format

• Table• Graph• Order• Considerations

• No infections• <1 predicted

Stratification type and time period

• Aggregate by• Hospital• Adult/PICU

and NICU• Unit

• Time period• Annual• Semi-annual • Quarterly

Interpretation

• Cues• Color• Symbols• Words

• SIR language

SIR data presentation: Components to consider

Always customize for your audience whenever possible.

Customizing the data: What numbers?

• Number of infections• Number of central line days• SIR

– Number of infections predicted– p-value– 95% confidence interval– Comparison data

• National• State• Other hospitals in same bedsize category• Hospital

• Historical data

Customizing the data: What format?

• Table• Graph• Order– Alphabetical by unit– Highest to lowest SIR

• How will you account for the situation where:– There are no infections?– <1 infection is predicted?

Customizing the data: What setting and time period?

• Setting– Hospital– Adult/pediatric ICU and neonatal ICU– Unit

• Time period– Annual– Semi-annual – Quarterly– Monthly

Customizing the data: How will you help your audience interpret?

• Cues– Color

• Red/yellow/green (“stoplight”)• Red/blue/green

– Symbols• Circles, triangles, squares• Arrows to show up or down trend

– Words• SIR language

– Expected/predicted– Fewer/less/better– Greater/more/worse– Similar/same

Questions?

Dana.Burshell@vdh.virginia.gov

Andrea.Alvarez@vdh.virginia.gov

To speak to any member of the VDH HAI Team: 804-864-8141

SIR 101 and 201 available online

• SIR 101: Interpretation and public reporting– Reviewed basic SIR calculation and interpretation– Introduced publicly available SIR reports

• NHSN, Hospital Compare, Virginia Department of Health

• SIR 201: Calculating the measure, generating reports, and presenting the data– Nuts and bolts, step-by-step presentation for IPs

• Archived and available at: http://www.vdh.virginia.gov/epidemiology/ surveillance/hai/communication.htm

SIR and surveillance resources

• NHSN e-News: SIRs Special Edition– http://www.cdc.gov/nhsn/PDFs/Newsletters/ N

HSN_NL_OCT_2010SE_final.pdf

• VDH HAI website – Surveillance– http://www.vdh.virginia.gov/Epidemiology/ Sur

veillance/HAI/SurveillanceReporting.htm