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Understanding and Using Measures for Healthcare-Associated Infections (HAI)
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Healthcare-associated infections (HAIs) are among the top causes of unnecessary illnesses and deaths in the United States. HAIs are infections that patients get while staying in a hospital or other healthcare facility – infections that the patients did not have before being admitted. They account for approximately 1.7 million infections and almost 100,000 deaths annually1. HAIs result in extra days of hospitalizations and higher health care costs. The estimated financial impact of HAIs is between $28 billion to $33 billion a year2.

HAIs and patient safety are major public health issues that require collaborations of government and the health care industry. Reducing preventable HAIs is a priority for the State and for New Jersey hospitals. Signed in 2007, Public Reporting Legislation (PL of 2007, C 196) requires hospitals to report HAI data to the State Department of Health and Senior Services for public reporting in the Hospital Performance Report.

This section of the report shows how well New Jersey hospitals are providing safe patient care by comparing hospital’s HAI experience with the national experience. It gives hospitals information to help reduce preventable HAIs and improve patient safety.

The HAI measures are calculated differently than the recommended care and PSI measures. The HAIs are not reported as scores or simple percentages; they are reported as Standardized Infection Ratios (SIR). More detailed explanations on SIR are provided below. Hospitals that performed better than the national experience have lower ratios. Lower ratios are better because they suggest fewer infections.  The label “L” in the tables identifies the better performing hospitals. Unlike recommended care measures and similar to PSIs, a lower ratio is better.

What HAIs are in this year’s report?

This year’s report focuses on three types of HAIs; Surgical Site Infections (SSIs) following Coronary Artery Bypass Graft (CABG) surgery, Abdominal Hysterectomy procedures, Knee Arthroplasty procedures (new to this year's report), Central Line-Associated Bloodstream Infections (CLABSIs), and Catheter-Associated Urinary Tract Infections (CAUTIs).

Where do the data come from?

New Jersey hospitals are required toreport SSI, CLABSI, and CAUTI events to the National Healthcare Safety Network (NHSN), a healthcare-associated infection surveillance and prevention system developed by the Centers for Disease Control and Prevention (CDC).

This report uses SSI data reported to NHSN by New Jersey hospitals in 2010. Surgical procedures which involve the placement of an implant must be followed for a year. As a result, surgery data will be reported a year behind the other HAI measures. CLABSI and CAUTI data in this report are from 2011.

Hospitals were provided the opportunity to verify the accuracy of their data. The data in this report have not been independently audited and validated.

What is Risk-Adjustment?

Hospitals have many differences. Some treat sicker or older patients tha nothers. Sicker patients who end up in the hospitals’ ICUs or CCUs are more likely to develop hospital-acquired infections. Hospitals affiliated with a medical school generally treat sicker patients than most hospitals. Not all hospitals have the same types of ICUs. For example, patients in burn units or trauma units are more at risk of acquiring infections. These differences make it difficult to fairly compare hospitals’ HAI experience.

The CDC uses a statistical method called “risk-adjustment” that standardizes the differences across hospitals and allows all hospitals to be measured more fairly. This method ‘adjusts’ for risk-factors that most often affect the risks of developing infections, such as type of ICUs, number of ICU beds, and hospitals affiliated with a medical school. This risk adjustment methodology was used on the NewJersey data to “even out the playing field”.

How are HAIs measured and what do the measures mean?

The Standardized Infection Ratio (SIR) is used to measure HAIs. The SIR is a summary measure developed by CDC to track HAI sat the national, state, local or hospital level over time. In basic terms, the hospital SIR is the total number of “observed” or actual events, also called infections, divided by the total number of “expected” events, which is derived from the national baseline experience. More detailed explanations of the “observed” and “expected” number of events as well as the SIR are provided below.

The hospital SIRs are compared to the national experience, which is a baseline SIR of 1.0. The results are summarized under the column, National Comparison. This column classifies the hospitals’ performances by an L as “Lower than Expected,” an S as “Similar to Expected”, or an H as “Higher than Expected.”

A hospital has performed better than the national baseline if the National Comparison is marked with an L. These hospitals appear better because they had fewer infections than what is predicted based on the national experience. Hospitals labeled with an H had more infections than what the national experience predicted. Those hospitals that performed the same as the national experience are labeled with an S.

According to CDC’s risk adjustment methodology, the SIR for the national baseline is 1.0. To interpret a hospital’s SIR, compare the hospital’s SIR to 1.0, the national baseline SIR. This approach compares a hospital’s actual performance to what would have occurred if the hospital performed the same as the national baseline experience.

To learn more about the risk-adjustment method and how SIRs are calculated, see the technical report.

Surgical Site Infections

What are Surgical Site Infections?

A surgical site infection (SSI) is an infection that occurs in the area of the body where the surgery took place. The SSI can be superficial, meaning it’s on the skin. It can also be serious and affect layers unde rthe skin, organs and/or implants.The infection must develop within 30 days of the procedure in order for the infection to be attributed to the surgical procedure. If the procedure involves an implant or transplant, monitoring for an SSI must occur for a year following the procedure.

According to the CDC, SSIs were the second most common HAI, accounting for 17 percent of all HAI hospitalizations.   Associated costs to treat an inpatient with a SSI are between $11,874 - $34,670 per infection.2  One article notes that more than 750,000 SSIs occur each year in the United States which results in an additional 2.5 million hospital days which leads to more than $1 billion in unnecessary costs.6

What Surgical Site Infections are in this report?

The surgical site infections which are included in this report are from 2010. The infections reported were inpatient procedures and Deep Incisional Primary and Organ/Space SSIs that were identified during admission or readmission. As noted previously, surgical procedures which involve an implant of any kind must be followed for a year.

This year’s report includes SSI data from Coronary Artery Bypass Graft(CABG) procedures, AbdominalHysterectomy procedures and Knee Arthroplasty procedures. It is important to note that only 18 of the 72 acute care hospitals are licensed as Open Heart Surgery hospitals and are able to perform CABG surgery. The surgical site infection data for 2010 were verified for accuracy by each hospital but were not audited.

What are the SSI results for New Jersey hospitals for 2010?

A total of 5,516 CABG procedures were reported in NHSN by the 18 Open Heart Surgery Hospitals in New Jersey. The formula below provides the Statewide observed, expected and SIR for CABGs:

Observed CABG infections=66
Expected CABG infections=68.15
SIR=Observed / Expected = 66/68.15 = 0.97

The SIR of 0.97 indicates that the observed CABG infections were 3% fewer than expected based on the national data. The difference is not statistically significant which means the CABG infections in New Jersey were similar to the CABG infections seen nationally.

A total of 8,036 Abdominal Hysterectomy (HYST) procedures were reported in NHSN by the hospitals in New Jersey who perform the procedure. The formula below provides the Statewide observed, expected and SIR for abdominal hysterectomies:

Observed HYST infections=49
Expected HYST infections=55.96
SIR=Observed / Expected = 49/55.96 = 0.88

The SIR of 0.88 indicates that the observed abdominal hysterectomy infections were 12% less than expected based on the national data. However, the difference is not statistically significant which means the abdominal hysterectomy infections in New Jersey were similar to those seen nationally.

A total of 13,054 Knee Arthroplasty procedures were reported in NHSN by hospitals in New Jersey who perform the procedure. The formula below provides the Statewide observed, the expected and the SIR for knee arthroplasties:

Observed KPRO infections = 77
Expected KPRO infections = 81.04
SIR=Observed/Expected = 77/81.04 = 0.95

The SIR of 0.95 indicates that the observed knee arthroplasty infections were 5% less than expected based on the national data. However, the difference is not statistically significant which means the knee arthroplasty infections in New Jersey were similar to those seen nationally.

The Overall SSI SIR takes into account all surgeries that were reported in New Jersey in 2010; CABG, Abdominal Hysterectomy and Knee Arthroplasty. There were more than 26,000 surgeries reported in NHSN by New Jersey hospitals. The formula below provides the Statewide observed, the expected and SIR for the Overall SSIs:

Observed SSIs = 192
Expected SSIs = 205.15
SIR=Observed / Expected =192/205.15 = 0.94

The SIR of 0.94 indicates that the Overall SSIs for New Jersey is 6% fewer than expected based on the national data. However, the difference is not statistically significant. This means the surgical site infections in New Jersey were similar to the surgical site infections seen nationally.

Central Line-Associated Bloodstream Infections (CLABSIs)

What are Central Line-Associated Bloodstream Infections (CLABSIs)?

CLABSIs are primary blood stream infections that are associated with the presence of a central vascular catheter. A central line is a tube that is placed into a patient’s large vein, usually in the neck, chest, arm or groin.The line is used to give fluids and medication, withdraw blood, and monitor the patient’s condition. A bloodstream infection can occur when microorganisms such asbacteria and/or fungi enter, attach and multiply on the tubing or influid administered through the tubing and then enter the blood.

If you develop a central line-associated blood–stream infection, you may become ill with fevers and chills or the skin around the central line may become sore and red. CLABSIs can be prevented through proper management of the central line. It is estimated that CLABSIs cost $2.7 billion a year in the United States. According to the CDC, approximately 250,000 CLABSIs occur annually with an estimated death rate of 12% to 25% for each CLABSI3.

What CLABSI data are included in this report? 

CLABSIs are monitored in many inpatient locations within the hospital. This report includes CLABSI events that occurred in adult, pediatric critical/intensive care units and neonatal intensive care units (CCUs or ICUs and NICUs) in each of the 72 acute care and specialty care hospitals in New Jersey during 2011. Most hospital-acquired infections occur in intensive care units, which have the sickest patients. It is important to note that the CLABSI data in this report were verified for accuracy by each hospital but were not audited.

What are the CLABSI results for New Jersey for 2011?

There were more than 273,000 central-line days reported to NHSN by New Jersey acute care hospitals in 2011. The formula below provides the Statewide observed, expected and SIR for CLABSIs:

Observed CLABSIs = 405
Expected CLABSIs =  556.34
SIR=Observed / Expected = 0.73

The SIR of 0.73 indicates that CLABSIs for New Jersey was 27% fewer than expected based on the national data. The difference is statistically significant. This means the central-line infections in New Jersey were lower than the central-line infections seen nationally.

Catheter-Associated Urinary Tract Infections (CAUTIs)

What are Catheter-Associated Urinary Tract Infections (CAUTIs)?

Catheter Associated Urinary Tract Infections (CAUTI) are the most commonly reported healthcare-associated infection in acute care hospitals. A catheter is a drainage tube that is inserted into the bladder.The catheter is left in place and is connected to a closed collection device.

More than 30 percent of infections in acute care hospitals are reported as CAUTIs.5 As with other HAIs, CAUTIs are also associated with increased morbidity, mortality, length of stay and hospital costs. It is estimated that more than 449,000 CAUTIs occur annually and patient hospital costs range from $862 to $1,007 per incident.2  CAUTIs are also associated with more than 13,000 deaths annually.5

What CAUTI data are included in this report?

CAUTIs are monitored in many inpatient locations within the hospital. This report focuses on CAUTI events that occurred in adult critical/intensive care units (CCUs or ICUs) in each of the 72 acute care and specialty care hospitals in New Jersey during 2011. This data is also from the NHSN system noted above. It is important to note that the CAUTI data in this report were verified for accuracy by each hospital but were not audited.

What are the CAUTI results for New Jersey for 2011?

There were over 315,000 catheter days reported to NHSN by New Jersey hospitals in 2011. The formula below provides the Statewide observed, expected and SIR for CAUTIs:

Observed CAUTIs = 610
Expected CAUTIs =  626.72
SIR=Observed / Expected = 0.97

The SIR of 0.97 indicates that CAUTIs for New Jersey is 3 % lower than the expected national data. The difference is not statistically significant. This means the catheter-associated urinary tract infections in New Jersey are similar to the catheter-associated urinary tract infections seen nationally.

What is “National Comparison”?

In addition to displaying the “observed” and “expected” numbers of events and the SIRs, the tables include a column labeled “National Comparison.” This column classifies the hospitals’ performances as an L which is Lower than expected, an S which is Similar to expected, or an H which is Higher than expected. A hospital performed better than the national baseline if the National Comparison has an L or Lower than Expected, as indicated in the table.

In trying to determine a hospital’s performance, it is important to account for the fact that some differences occur simply due to chance. Although not shown in the table, 95% confidence intervals are used to determine how statistically certain is the conclusion that a hospital’s SIR is higher or lower than 1.0. For more details, refer to the HAI Technical Report at HAI Technical Report.

A hospital’s SIR is statistically significantly lower than 1.0 if its 95% confidence interval falls completely below 1.0. The hospital is noted with an L in the National Comparison column. This means that fewer HAI events were observed than expected, adjusting for differences in the types of patients treated. Since the comparison is to the national baseline data, the hospital performed better than the nationa lbaseline experience.

A hospital’s SIR is statistically significantly higher than 1.0 if its 95% confidence interval falls completely above 1.0. In this case, the hospital is noted with an H in the National Comparison column. This means that more HAI events were observed than expected, adjusting for differences in the types of patients treated and that the hospital performed worse than the national baseline experience.

A hospital’s SIR is not statistically different from 1.0 if its 95% confidence interval includes 1.0. The hospital is noted with an S in the National Comparison column. This means that adjusting for difference in the types of patients treated, the hospital’s performance on preventing HAI events was similar to the national baseline experience.

Can we make conclusions about a hospital’s performance in preventing HAIs based on this data?

Please keep in mind the following before making conclusions about a hospital:

Even though hospitals reviewed and verified the data used in this report, the data have not been audited by an independent agency.

It is also important to note that a hospital which performed lower than the National Comparison does not necessarily mean the hospital is better but that they may need to improve their HAI surveillance protocols. Conversely, a hospital which performed higher than the National Comparison is not necessarily a poor performer. This hospital could have better infection surveillance protocols and processes instituted throughout their facility.

In addition, the risk-adjustment method may not fully capture how sick patients are in certain hospitals and locations. The sicker the patients are, the more likely a hospital is to have a higher number of events. Therefore, it is important to use caution when interpreting the hospital infection data. 


1Centers for Disease Control and Prevention: Estimates of Healthcare-Associated Infections. http://www.cdc.gov/ncidod/dhqp/hai.html accessed February 25, 2013.

2 Scott, RD. The Direct MedicalCosts of Healthcare-Associated Infections in U.S. Hospitals and the Benefits of Prevention. http://www.cdc.gov/HAI/pdfs/hai/Scott_CostPaper.pdf accessed February 25, 2013.

3 Centers for Disease Control and Prevention: Slides for the American Recovery and Reinvestment Act Epidemiology and Laboratory Capacity (ELC) for Infectious Disease Program, Healthcare-Associated Infections (HAIs) Grantee Meeting October 19-20, 2009,  presented by Katherine Allen-Bridson http://www.cdc.gov/hai/recoveryAct/PDF/Oct09/11-145_Bridson_NHSN_CLABSI_Day2_Workshop1.pdf  accessed February 25, 2013. .

4 Centers for Disease Control andPrevention, APIC, JointCommission, IDSA, AHA, SHEA, FAQ Sheet about “Catheter-Associated Bloodstream Infections” http://www.cdc.gov/ncidod/dhqp/pdf/guidelines/BSI_tagged.pdf  accessed February 25, 2013.

5 Klevens RM, Edward JR, et al. Estimating health care-associated infections and deaths in U.S. hospitals, 2002. Public Health Reports 2007; 122:160-166.

6 Edmiston, CE, Spencer, M, Lewis, BD, et al., Reducing the Risk of Surgical Site Infections: Did We Really Think SCIP Was Going to Lead Us to the Promised Land? Surgical Infections 2011; 12(3):169-177.

To view more information on HAIs, click on one of the following links:

 Preventing Central Line-Associated Bloodstream Infections

 HAI Data

To view information on other measures, click on the following link:

 Using the Information on this Website


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Last Modified: Thursday June 27 2013