PREVALENCE & INCIDENCE Contents Prevalence.................................... 2 Point Prevalence...................................... 3 Period Prevalence..................................... 4 Incidence.................................... 4 Cumulative Incidence................................. 4 Incidence Density..................................... 5 Prevalence and Incidence in Your Facility........... 7 1
Pressure Ulcers are defined as localized injury to the skin and/or underlying tissue usually over a bony prominence, as a result of pressure, or pressure in combination with shear and/or friction. A number of contributing or confounding factors are also associated with pressure ulcers; the significance of these factors is yet to be elucidated. Measurement of the frequency of these ulcers is necessary to characterize and monitor the magnitude and severity of the problem in different care settings. This is accomplished by monitoring the prevalence and incidence of pressure ulcer formation. The value of calculating prevalence and incidence data for a particular facility or agency is to compare rates over time to determine what changes have occurred, and allows for benchmarking and trending against previously collected data (either baseline or national). Prevalence and incidence are used to examine the scope of the problem from different perspectives in any given care setting. DID YOU KNOW Prevalence is the proportion of persons who have a condition at a specific point in time, whereas incidence is the proportion of at-risk persons who develop the condition over a specific period of time. Prevalence is the proportion of persons who have a condition at a specific point in time, whereas incidence is the proportion of at-risk persons who develop the condition over a specific period of time. Individuals in the incidence group automatically count in period prevalence and remain in these statistics until recovery, discharge or death. Because patients may develop pressure ulcers in one healthcare facility and then be transferred to another facility, prevalence can be adversely affected on any given day. Therefore, the incidence of new pressure ulcers is a more appropriate criterion to use for quality of care assessment. For this reason, it is important that prevalence and incidence of pressure ulcers be differentiated. Prevalence Prevalence refers to the cross-sectional view of the number of both new and old cases at any one time in the population, such as the proportion of patients in a long-term care facility with pressure ulcers on a specific day. The time can be defined as a snap shot of the occurrence at one point in time (point prevalence) or over a short period of time (period prevalence). 2
Pressure Ulcer Point Prevalence = Number of people with a pressure ulcer x 100 Number of people in a population at a specific point in time Pressure Ulcer Period Prevalence = Number of people with a pressure ulcer x 100 Number of people in a population during a particular period in time Process: Point Prevalence Point prevalence is determined by defining the population to be studied and the single point in time. 1. The first step is to identify the individuals at risk for pressure ulcer development using a validated risk assessment tool such as the Braden or Norton Plus pressure ulcer scale on a specific day. The number of people in the defined population becomes the denominator (written below the line) in the point prevalence equation. Consider the outcome of the equation if the population were defined as all patients in long-term care facilities. It is essential that the population is defined to ensure that accurate comparisons can be made. It would not be valid to compare data on at-risk populations with figures that included all types of patients. 2. Next, assess all patients in the study population to determine if they have a pressure ulcer. The number of people with a pressure ulcer is the numerator (written above the line) in the point prevalence equation. 3. The numerator (top number) is divided by the denominator (bottom number), and then multiplied by 100 to determine the point prevalence rate. 3
Period Prevalence Period prevalence includes the number of patients who have a pressure ulcer at the beginning of a specific period of time and those patients that develop NEW pressure ulcers during that specific period of time. The steps in calculating period prevalence are identical to point prevalence except that the population is defined as the people who meet the criteria over the study period of time. For example, all patients in an assisted-living facility during a one-month period. This is the denominator of the formula. The study population is fixed. Only patients present at the beginning of the study are observed over the defined study period. Patients that are admitted during the study period are not included. The numerator in the formula is all of the patients in the study population that have a pressure ulcer, or who develop one during the study period. The numerator is divided by the denominator, and then multiplied by 100 to determine the period prevalence. Period prevalence is not used as commonly as point prevalence because it combines already existing pressure ulcers with newly developed pressure ulcers in arriving at the prevalence. Thus, the data is not pure. Incidence Incidence refers to the rate at which new cases occur in a particular population, over an extended and specific time period. An example is the number of new cases per year among the patients at a long-term care facility. It can be calculated for a specific nursing unit, type of patient, or an entire facility. Therefore, it may be used to determine rates across the continuum of care. Incidence can be computed as cumulative incidence or as incidence density. Cumulative Incidence Cumulative incidence is the rate of new pressure ulcers in a group of patients of fixed size, all of whom are observed over a period of time. 4
Pressure Ulcer Cumulative Incidence = Number of people with a new pressure ulcer x 100 Total number of people in a population at the beginning of the time period Incidence Density Incidence density is the number of new cases of pressure ulcers that occur in an ever-changing patient population, such as a nursing home. In order to be consistent with patients and follow-up intervals, the denominator is not persons in the setting for a specific time period, but person-time in a setting. In computing incidence, person-time is commonly expressed in units of 1000 patient days. Therefore, incidence is calculated as the number of persons developing pressure ulcers per 1000 patient days. This is referred to as incidence density. Number of people with a new pressure ulcer Pressure Ulcer Incidence Density = x 1000 = number of people developing a pressure ulcer Total patient days free of ulcers x 1000 = 1000 patient days 5
Process: Calculating Pressure Ulcer Incidence 1. Define the population to be studied. Consistent with the methodology for measuring prevalence, the population in an incidence study includes all people in a geographically defined setting, such as a rehabilitation unit. The population is followed over time. When measuring cumulative incidence, the number of persons who meet the defined criteria for the population becomes the denominator in the incidence formula. When incidence density is being computed, the number of days each person in the defined population is in the study and free of pressure ulcers is calculated to produce the denominator in the incidence formula. 2. Assess all patients to determine if they have a pressure ulcer. Those with ulcers are excluded from further study; those free of ulcers are followed to determine if they develop new ulcers. 3. Assessments are to be conducted at regular predetermined intervals on the defined population of patients to calculate how many patients develop a new pressure ulcer during the study time period. This number is the numerator in the incidence formula. The group of patients followed over time remains fixed. Any new patient admitted during the followup period is not added to the group. 4. Cumulative incidence rate is the number of new ulcers (numerator), divided by the number of patients in the defined population at the start of the study period (denominator) multiplied by 100. 5. Incidence density is calculated by adding up the number of days each patient in the defined population was without a pressure ulcer. When a patient develops a pressure ulcer, they are no longer followed; this patient is counted as a case in the numerator and as part of the total group in the denominator. The total number of days each patient in the specified population is without a pressure ulcer (denominator) is multiplied by 1000. Similarly, the total number of patients who develop a pressure ulcer (numerator) is multiplied by 1000. By multiplying the numerator and denominator by 1000, the value of the quotient does not change, but the denominator becomes 1000 patient days. Thus, incidence density is expressed as the number of patients who develop new ulcers per 1000 patient days. 6
Calculating prevalence and incidence is valuable because it provides comparison data to determine what changes have occurred in the frequency of pressure ulcers over time. This can only be accomplished by benchmarking and trending against previously collected data (baseline, regional or national). Given that some patients may have existing pressure ulcers that developed while in another healthcare facility, the incidence of new pressure ulcers is a more appropriate criterion to use for quality of care assessment. Prevalence and Incidence in Your Facility Prevalence is an indicator of the care burden in a facility, while incidence is an indication of the quality of care provided in a facility. Prevalence is a good point-in-time indicator of the resources needed to provide quality care in the facility and needed improvements within a facility. Patients are admitted to healthcare facilities at an uncontrolled rate; therefore, prevalence cannot be controlled at any specific point in time by a facility because the patient population consists of patients with both admitted and facility-acquired pressure ulcers. The prevalence rate also must be determined as a baseline measurement in preparation for conducting and monitoring incidence of pressure ulcers. Incidence is important in measuring the quality of care provided to prevent and treat pressure ulcers. Incidence is the yardstick by which surveyors and consumers measure a facility s ability to deliver quality care. It is also important to define a realistic time frame for the study to adequately sample a representative group of patients that are cared for in the facility, avoiding an atypical situation. Furthermore, since studies show that the occurrence of pressure ulcers can vary widely from one month to another, an extended time frame will provide a more valid indication of the occurrence of new pressure ulcers in the facility. Based on best practice standards, all policies, procedures, protocols and communication processes should be directed toward prevention and treatment of pressure ulcers and improvement of current practices. 7
Prevalence and incidence together help determine the potential for improvement in wound management processes. This may include changes to policies, procedures, and protocols to improve clinical and financial outcomes. Ultimately, the fundamental question to be addressed by all healthcare providers is: Did we accurately identify risk status and take appropriate measures to prevent the pressure ulcer? References: Cuddigan J, Berlowitz DR, Ayello EA. Pressure ulcers in america: prevalence, incidence, and implications for the future. Advances in Skin & Wound Care. July/August 2001. National Pressure Ulcer Advisory Panel. Cuddigan J; Ayello EA, Sussman C, eds. Pressure ulcers in America: Prevalence, incidence, and implications for the future. Reston, Va. NPUAP. 2001. National Pressure Ulcer Advisory Panel National Conference. Frantz R. Prevalence, Incidence and Outcomes Measurement. Washington, D.C. NPUAP. February 2001. National Pressure Ulcer Advisory Panel. The New Revised 2007 Pressure Ulcer Stages, Definitions, and Descriptions page. Available at: http://www.npuap.org/documents/npuap2007_pu_def_and_descriptions.pdf. Accessed February 28, 2007. 8