MSDH collects data on CMS reportable HAIs from the National Healthcare Safety Network (NHSN), and reportable diseases reported by laboratories and clinicians. Facilities self-report infections; therefore, there might be some discrepancy in the actual number of infections. Some facilities might under- or over-report infection rates. The data is analyzed and the following metrics are used to summarize the findings.
- Incidence Rate: The incidence rate is a measure that standardizes the infection count based on the population at risk of infection, allowing for comparison between units and facilities. This metric is not adjusted for any risks factors (Equation 1).
Eq.1. Rate (per 1,000 device days) = (number of infections/number of at risk population) x 1,000
*At-risk population is central line days for CLABSI, catheter days for CAUTI, surgeries performed for SSI:Colo and SSI:Hyst, 1,000 patient days for MRSA and CDI, and 100,000 residents for VRE, VISA, and VRSA. Population numbers are estimated based on statistical projections from the most recent decennial census. Actual population sizes may vary from what is estimated.
- Device Days: The number of device days is the number of days each patient has a device (e.g., central line or catheter), all added together.
- Patient Days: The number of patient days is the number of days each patient was in the facility, all added together.
- Patient Months: The number of patient months is the number of months each patient was on hemodialysis, all added together.
- Standardized Infection Ratio: The SIR is calculated by dividing the number of infections by the expected number of infections. The number of expected infections is calculated using NHSN. An SIR is not calculated when the expected number of infections is less than one (Equation 2).
Eq.2. SIR = number of observed cases/number of expected cases
*SIR Limitation: The SIR is calculated using baseline data that was collected by the CDC from a sample of facilities. The baseline data for CLABSI and SSI was collected from 2006-2008, for CAUTI was 2009, and for CDI and MRSA was 2010-2011. This baseline is used to find a risk-adjusted number of expected infections. The risk factors used are likely to have changed based on improved infection control practices, changes in case definitions, and improved reporting by facilities. Caution must be used when comparing facility rates to the national baseline. For this reason, the District specific SIR will be compared to the state SIR as a reference with similar demographics and baseline.
- Estimated Costs: A study published by the CDC in 2009 estimated the costs of a select list of HAIs.1 Using these 2007 prices, the costs for a HAI was estimated, using the Bureau of Labor Statistic's Consumer Price Index (CPI) to adjust for inflation. The inpatient hospital services category of the CPI (CPI-IP) for All Urban Consumers was used to determine inflation adjustments.2
For MRSA bacteremia, a paper published in 1999 was used to estimate costs for treatment, and prices were adjusted to 2014 dollars.3 These costs are rough estimates and may over- or under-estimate the actual costs incurred by payers in 2014 since technology has changed since 2007 and 1999 (Equation 3).
Eq.3. Estimated Costs (per infection) = 2007 cost of infection [1 + (2009 CPI-IP − 2011 CPI-IP)/2009 CPI-IP)]
- Scott, RD II. The Direct Medical Costs of Healthcare-Associated Infections in U.S. Hospitals and the Benefits of Prevention. The Center for Disease Control and Prevention. March 2009. Available: http://www.cdc.gov/HAI/pdfs/hai/Scott_CostPaper.pdf.
- Bureau of Labor Statistics. Consumer Price Index. Available: http://www.bls.gov/cpi/cpi_dr.htm.
- Abramson, MA, Sexton, DJ. Nosocomial Methicillin-Resistant and Methicillin-Susceptible Staphylococcus aureus Primary Bacteremia: At What Costs? Infection Control and Hospital Epidemiology. June 1999. 20(6). 408-411. doi: dx.doi.org/10.1086/501641.