Definitions

Ambulatory surgery center (ASC)
Central line
Central line days (CLDs)
Central line-associated bloodstream (CLAB) infection
Central line-associated bloodstream (CLAB) infection rate
Department reporting
Expected number of infections
Healthcare-Associated infection (HAI)
Head of Bed (HOB) Elevation
Head of Bed (HOB) Elevation - Contraindication
Hospital reporting criteria
Hospital reporting period
Intensive care unit (ICU)
Risk Adjustment
Significance tests
Surgical Site Infections
Type of Operative Procedure (Surgery) for which SSIs are reported
Ventilator-Associated Pneumonia (VAP)

Ambulatory surgery center (ASC)
Typically a freestanding healthcare facility that does not keep patients overnight and that performs surgical procedures rather than providing standard office care.

back to top

Central line
A flexible tube that terminates close to the patient's heart or in one of the large veins or arteries. A central line is needed to give fluids, medication, withdraw blood, and for monitoring the patient's condition.

back to top

Central line-days (CLDs)
The total number of days a central line is in place for each patient in the intensive care unit (ICU). The count is performed each day, and each patient with a central line is counted as a central line-day.

back to top

Central line-associated bloodstream (CLAB) infection
If an infection occurs within 48 hours of the use of a central line, it is assumed to be a CLAB infection.

back to top

Central line-associated bloodstream (CLAB) infection rate
The CLAB infection rate is defined as the number of CLAB infections per 1000 central line-days. If a hospital intensive care unit (ICU) had 5 infections and 100 central line-days, their rate would be calculated as follows: 5/100 = .05 infections per central line-days X 1000 = a rate of 50 central line infections per 1000 central line-days

back to top

Department reporting
Through this web site, the Missouri Department of Health & Senior Services (DHSS) reports 12 months of central line-associated bloodstream (CLAB) infection data and surgical site infection (SSI) data. The data reflect the most recent 12-month period available. The department is in the process of developing a system to allow searches of infection data from previous years.

back to top

Expected number of infections
A facility's infection rate is compared to the infection rate of a reference group. This is done by comparing the number of infections reported by the facility to the 'expected number' of infections. 'Expected' in this usage does not mean what we would expect based on something we know about the hospital. Instead, it refers to the number of infections that we would expect if the hospital had the same infection rate as the comparison group.

The expected number is obtained by applying the rate of the comparison group to the number of central line-days reported by the hospital. For example, a hospital reports 4 patients with infections and 500 central line-days. If the rate for the comparison group (all reporting hospitals in the state) is 2.8 CLABs per 1000 central line-days, this equates to a proportion of .0028 (2.8/1000). Applying this proportion to the 500 central line-days results in 1.4 'expected' infections for the hospital (.0028 X 500 = 1.4).

back to top

Head of Bed (HOB) Elevation
Positioning the bed so the patient’s upper body is slightly elevated rather than lying flat. It is recommended that patients on a ventilator have their HOB elevated to 30-degrees or greater in order to help prevent pneumonia.

back to top

Head of Bed (HOB) Elevation - Contraindication
A contraindication is a medical reason for not performing a particular therapy which is otherwise adviseable. Contraindicators for elevating the head-of-bed in excess of 29 degrees include, but are not limited to, severe head wounds, severe burns on the upper body, or other malady that would prevent the head and upper body from being raised for any extended pperiod of time.

back to top

Healthcare-associated infection (HAI)
A healthcare-associated infection is an infection that occurs in a patient as a result of being in a healthcare setting.

back to top

Hospital and Ambulatory Surgery Center (ASC) reporting criteria
By April 1 of each year, all hospitals must report the number of central line-days in selected ICUs during the previous calendar year. Hospitals are exempt from reporting for any of the selected ICUs that had less than 50 central line-days during the previous calendar year. By April 1 of each year, all hospitals and ASCs must report the number of selected surgeries performed during the previous calendar year. Facilities are exempt from reporting for any of the selected surgeries where fewer than 20 were performed during the previous calendar year.

back to top

Facility reporting period
The 12-month period during which qualifying facilities must report to the department the number of central line-days, central line-associated bloodstream (CLAB) infections, surgical procedures, and surgcial site infections (SSIs) they experience. During this period, facilities must report within 60 days of the end of each month.

back to top

Intensive care unit (ICU)
A nursing care unit that provides intensive observation, diagnosis, and therapeutic procedures for patients who are critically ill. For HAI reporting, ICUs are designated

  • Coronary
  • Medical
  • Surgical
  • Medical/Surgical
  • Pediatric
  • Neo-Natal (NICU)
Any other ICU data will be grouped together under heading “Other”, where applicable.

back to top

Risk Adjustment
The performance of each facility in preventing Surgical Site Infections has been adjusted to reflect the higher risk of infections associated with certain procedures. Adjusting for these risk levels allows for fairer comparisons among the facilities. If a facility has a high infection rate after the adjustment, viewers of the data can have more confidence that the higher rate is the result of a problem with surgical site infections and not merely the result of treating a large number of high-risk patients.

Here is a detailed look at the basis for the adjustments and how they are calculated:

Risk factor scores for a procedure can vary from 0 to 3, with 3 representing the highest probability of an infection. Risk scores are the sum of scores for three component factors, each of which contributes a 0 or 1 to the total score. The component risk factors that are used in adjusting a facility’s performance are:

  •  the degree of contamination of the wound at the time of the operation
  • the duration of the procedure
  •  the American Society of Anesthesiologists (ASA) score. This score is an evaluation of the patient’s physical condition.

Occasionally overall risk factor scores are merged, as in “2, 3”. For these surgical procedures, the Centers for Disease Control found that SSI rates were similar whether the overall risk score was a 2 or a 3.

One component, the duration of the procedure, has changed over time. Prior to 2006, the risk score was assigned based on the number of hours needed to complete the procedure. For example, a hip prosthesis procedure that lasted more than 2 hours was assigned a 1, which was then combined with the other two factors to come up with that patient’s total risk score.  

Beginning with 2006 and 2007 data, the standard was changed to the 75th percentile of the distribution of durations to determine the point at which a duration factor would contribute a 1 to the overall risk factor score. Under the new standard, a hip prosthesis procedure that lasted more than 123 minutes resulted in a ‘1’ being contributed to the overall risk score. (This data was published in November 2008, Edwards JR, et al, National Health Care Safety Network report, data summary for 2006 through 2007. Am J Infect Control 2008; 36:609-26.)

Missouri does not collect procedure duration data in minutes from the facilities and therefore continues to use the pre-2006 standard based on hours. Data are collected on three procedures for hospitals – hip prosthesis, abdominal hysterectomy and coronary artery bypass with chest and donor incision.

For coronary bypass surgery, the 75th percentile standard published in 2008 is the same as the previous standard – 300 minutes or 5 hours.  For hip prosthesis surgery, the national standard is 3 minutes longer than in Missouri -- 123 minutes vs. 2 hours. For abdominal hysterectomy, the standard was 18 minutes longer than in Missouri – 138 minutes vs.  2 hours.

Since Missouri uses the prior standard, this means that Missouri facilities would have slightly higher risk scores for abdominal hysterectomy and hip prosthesis procedures than they would if the 75th percentile standard had been used. For example, a hip prosthesis procedure lasting 122 minutes would result in a ‘1’ being added to the risk score for Missouri facilities because the procedure lasted more than two hours. Facilities using the 123-minute standard would have a ‘0’ added, and would therefore have a lower overall risk score for the same procedure. At some point in the future, we plan to follow NHSN’s lead by collecting procedure duration data in minutes.

To put Missouri’s data into perspective, users often want to make comparisons to U.S. data. For that reason, a column is included in our HAI tables labeled “Hospital Performance Compared with Facilities in U.S.” This column is based on the annual National Health Care Safety Network publications, known as NHSN.  

However, hospitals that report to NHSN are not a random sample of hospitals in the U.S., and NHSN’s annual publications do not cover the same time periods as Missouri data, which are updated quarterly. And, as described above, Missouri and NHSN no longer define duration risk the same way. These differences make NHSN data a less-than-optimal basis for comparison. Nevertheless, the department’s staff believes that including a comparison with their data in our tables still helps users put Missouri data into a reasonable context and perspective.

back to top

Significance tests

Test for chance factors
Tests of statistical significance are needed to tell us whether the number of infections in an ICU or a facility is unusually high or low relative to the number we would expect if the facility had the same infection rate as a reference group. For example, suppose a relevant reference group (such as all reporting medical ICUs in the state) has a rate of 10 infections for every 1000 central line-days. Then, all other things being equal, a medical ICU that has twice the number of central line-days, or 2000, would be expected to have about twice the number of infections, or 20. However, the ICU is not likely to have exactly 20 infections during the year, and if it has a few more or less, we would attribute it to chance factors and normal fluctuation. If an ICU has many more (or less) than the expected number, we should be less certain that this was due to chance factors. In fact, we should be concerned that this rate is too high and maybe the facility is having a problem with infections. The function of the statistical test, then, is to help us determine at what point we should become concerned--at what point is the high (or low) rate not likely to be due to chance factors.  

Significant results
When a statistical test is performed on the number of infections in a facility or ICU and the test suggests that there are fewer infections than expected, or more infections than expected, based on the reference group rate, the results of the test are said to be ‘significant’ or ‘statistically significant’. If the test is performed and the number of infections is found to be within the range of what is expected, the results are said to be ‘statistically insignificant’ or ‘non significant’. Because of the way in which statistical tests are performed, significant results are generally more informative than non-significant results.  If a facility does not treat unusually severe patients and it also has significantly more infections than the expected number, it is safest to assume that the facility is having a problem with infections. At least consumers should be concerned enough to investigate further if they are considering treatment at the facility. If a facility treats patients with varying degrees of severity and also has significantly fewer infections than the expected number, then it is probably doing a good job of keeping health care-related infections under control.

Non-significant results
When the number of infections in a facility or ICU is not significantly different from the expected number, the interpretation is more ambiguous.  If an ICU has a small number of central line-days or a facility has a small number of surgeries, chance will play a bigger role in the observed infection rate, the number of infections will fluctuate more from year to year, and it is likely that the number of infections will not be significantly different from the expected number. However, the facility could still be doing a poor job or a very good job of controlling infections. If a number of years of data were combined in order to minimize the role of chance factors, the number of infections might be seen to be lower or higher than expected based on the reference group rate for the same number of years.

Confidence Intervals
For the data on this site, the significance tests were done by comparing the expected number of infections to confidence intervals (CI) around the reported number of infections. To oversimplify, the CI expresses the influence of chance on the reported rate. For example, if an ICU had 10 infections for the year, the confidence interval would be 4.7-18.3.  If the expected number of infections is lower than 4.7, the CI indicates that 10 is significantly higher than expected; if the expected number is above 18.3, then the CI indicates that 10 is significantly lower than expected; if the expected number is 4.7, or 18.3, or anywhere in between, then the CI indicates that 10 is not significantly different from the expected number.

The confidence intervals are exact poisson confidence intervals calculated by using the inverse gamma function as proposed by Leslie Daly ( 0 infections have a 95% confidence interval of 0 – 3.689.): Daly, L. The Calculation of Exact Binomial and Poisson Confidence Limits; Comput. Biol. Med., Vol. 22, No. 5, pp 351-361, 1992.

back to top

Surgical Site Infections
Surgical Site Infections (SSIs) are infections that are directly related to an operative procedure. Some SSIs are minor and only involve the skin or subcutaneous tissue. Other SSIs may be deeper and more serious.

back to top

Type of Operative Procedure (Surgery) for which SSIs are reported

CLAB Infection Rate Comparisons
Tests of significance are needed to tell us whether the number of infections in a facility is unusually high or low relative to the number we would expect if the facility had the same rate as a reference group. One type of significance test consists of calculating a confidence interval (CI), or range of values, around the number of infections in the facility. This CI can be thought of as the typical fluctuation in the number of infections in the facility. For example, the number of infections might be 10, with a CI of 5-15. This CI is then compared to the expected number of infections that we have calculated. If the expected number falls within the CI (between 5 and 15), the facility rate and the reference group rate are considered to be similar. In such cases, the hospital ICU will have a circle that is half full () in the Hospital Comparison and Profile tables. If the expected number is above the CI (any number above 15 in this example), the facility rate is considered to be significantly lower than the comparison group rate, and the hospital has a full circle () in the tables. If the expected number is lower than the CI (any number below 5 in this example), then the facility rate is considered to be higher than the comparison group rate, and the hospital has an empty circle ().

back to top

Ventilator-Associated Pneumonia (VAP)
An inflammatory infection in the lungs that occurs in a patient who is on a ventilator at the time of, or within 48 hours, before onset of the infection.