Pharmacy in Public Health: Epidemiology Course, date, etc. info

Learning Objectives Explain how epidemiology is used in public health List the different types of epidemiology studies and give an example of a study design used for each type Given an epidemiological measure of disease, explain what it means Given data about a disease in a population, calculate prevalence, incidence, relative risk, and/or odds ratio

Introduction Epidemiology is the study of disease in a population; it is considered the science of public health Studies the determinants and distribution of disease Assumes disease does NOT occur at random If causes can be identified, disease may be prevented It is a collection of study designs and methods for calculating disease rates Pharmacoepidemiology is a subset that focuses on medication-related disease

Key Assumption: Exposure-then-Disease Figure 10.2

EXAMPLE Using the death rates given below, what can you say about premature death risk in the population? SES:MaleFemale ChildAdultChildAdult High0%67%0%3% Medium0%92%0%14% Low73%84%55%54% Unknown--N/A---78%--N/A---13% Death Rates from a Single Cause by Gender, Age, & Economic Status Adapted from Simonoff, 1997

Roles for Epi in Public Health Monitor health of a population Respond to emerging public health problems Promote research and use of evidence-based interventions Evaluate effectiveness of a program Develop public health policy and law Set funding priorities for research and intervention programs

Understanding an Outbreak Epidemiology is used to better understand a disease outbreak by answering these questions – What is it? – How big is the outbreak? – Who is affected by the disease? – Where is the disease occurring? – When does the disease occur? – Why does the disease occur?

Measures of Disease Frequency Prevalence (total number of cases) Incidence (number of new cases) Mortality (number of deaths) EXAMPLE: In the past month, Town A reported five new cases of HIV/AIDS. This brings the total number of HIV/AIDS cases this year to 26. In Town B, there were 10 new cases and over 100 total cases during the same time periods.

Prevalence rates Need an indication of how the number of cases relates to the population Prevalence rate Total number of cases during a specified time period divided by the population count

Calculating a Prevalence Rate EXAMPLE Five new cases of HIV/AIDS were reported. This brings the total number of active HIV/AIDS cases this year (2006) to 56; total population is 100,000 and population at risk if HIV/AIDS is 20,000 Prevalence rate calculation: Prevalence rate (P) = 56 active HIV/AIDS cases /100,000 total population P = 56 per 100,000 (in 2006) Prevalence rates are increased by: An increase in the number of new cases (↑ incidence) A reduction in deaths due to disease (↓ mortality) New treatments that prolong life but not cure the disease Prevalence rates are decreased by: Reduced number of new cases Increased number of cures

Cumulative Incidence rates Incidence rates Cumulative incidence rate (number of new cases in a specified time period divided by number of population that is at risk of the disease)

Incidence Rates / Incidence Density Incidence Rates Incidence rate or density (number of new cases in a specified time period divided by the total number of person-time when at risk)

Comparing Incidence Rates EXAMPLE: Five new cases of HIV/AIDS were reported. This brings the total number of HIV/AIDS cases this year to 56; total population is 100,000 and population at risk of HIV/AIDS is 20,000. Suppose the actual time at risk for any one individual is estimated at 183 days per year (= 0.5 years per individual). Cumulative Incidence Rate calculation for one year: Use 5 new cases and 20,000 at-risk individuals CI = 5/20,000 (=25/100,000) Incidence Rate calculation for person-years: Use 5 new cases in numerator; Adjust denominator: 20,000p x 0.5y/p = 10,000 person-years IR = 5/10,000 (=50/100,000)

Example: Calculation of annual Incidence Density for suspected medication-related hyperthyroidism cases for the Clinic Total population at the start of the year was 200 There were 16 new cases of medication-related hyperthyroidism No new patients were admitted, but 10 patients left during the year: 5 left at 3 months (0.25year) = 5 persons x 0.25years = 1.25person-years 3 left at 6 months (0.5year) = 3 persons x 0.5years = 1.5 person-years 2 left at 9 months (0.75 years)=2 persons x 0.75years = 1.5 person-years Person-years for patients leaving the clinic: 4.25 person-years 190 stay all 12 months (1year) = 190 persons x 1year = 190 person-years Total person-years for denominator is = Incidence Density = 16 / = 8.24% Figure 10.6

Study Designs There are three main categories of epidemiology studies – Descriptive – Analytical – Interventional Potential disease risks are often identified in descriptive studies then studied in analytical and interventional designs

Descriptive Study Designs There are three types of study designs 1.Case report (or case series) 2.Cross-sectional 3.Correlational They differ in these ways: – Ability to tie cause to effect – Ability to allow comparisons across time or with other groups

Summary of Descriptive Designs Characteristic Individual-level data Population-level data Links cause-effect Timeline measured Allows comparisons to other groups Observational Experimental Case XXX --- XX XXX --- XXX --- Correlate Cross- Section --- XXX --- XXX --- XXX --- X --- XXX ---

Analytic Study Designs These designs must be able to: Establish that exposure preceded disease Determine if risk factor is necessary and/or sufficient Determine if risk factor is a direct or indirect cause Rule out confounding factors Eliminate or reduce systematic bias Two basic types: 1.Cohort 2.Case control

Cohort Study Use two groups of subjects – Subjects selected on basis of exposure status Exposed Not exposed May be prospective or retrospective Seeks to determine whether an exposure affects the likelihood that a person will get the disease Results usually reported as Relative Risk

Calculating Relative Risk using a 2x2 Table Figure 10.8 A ratio of percent of exposed individuals who get the disease compared to percent of not-exposed people who get the disease

EXAMPLE - Calculating Relative Risk Figure 10.8 Interpreting results: RR >1; exposure increases risk of disease RR=1; no difference due to exposure RR<1; exposure is protective and reduces risk of disease or When 95% CI includes a “1” then no difference in risk is seen (such as 95% CI of 0.55 – 3.6) DiseaseNo Disease Exposed Not Exposed RR = a/(a+c) ÷(c/(c+d) = 300/450 ÷ 150/500 = 2.23

Case Control Study Use two groups of subjects – Subjects selected on basis of disease status Disease No Disease Retrospective only Seeks to determine whether a person with the disease was more likely exposed to the risk factor than someone without the disease Results usually reported as odds ratios

Calculating an Odds Ratio (Cross-Products Ratio) Figure A ratio of the probabilities diseased individuals were/were not exposed is compared to the ratio of probabilities that disease-free people were/were not exposed

EXAMPLE - Calculating Odds Ratio Figure 10.8 Interpreting results: OR >1; person with disease was more likely exposed OR=1; no difference in exposure likelihood OR<1; person with disease was less likely exposed or When 95% CI includes a “1” then no difference in likelihood of exposure (such as 95% CI of 0.25 – 2.7) DiseaseNo Disease Exposed Not Exposed OR = (a/c) ÷(b/d) = (300/150)÷ (200/350) = 2/ = 3.5

Interventional Study Designs Use same approach as experimental design Random assignment to study arms Researcher controls the exposure Indirect method for learning more about a disease Used to test the effects of removing risk factors or adding protective factors on subsequent disease development Never used to directly test whether an exposure causes a disease

Summary Epidemiology is the scientific tool used in public health to describe disease behavior and distribution within a population; Measures of disease frequency include prevalence, incidence, and mortality rates; Study designs are used to establish exposure- to-disease associations and timelines, and Pharmacoepidemiology is the application of these methods to study adverse events after a medication is approved.

Case Example The following slides are optional

Handwritten prescription and label placed on prescription vial Figure 10.1

Population level data for Clinic Patients with medication-related Hyperthyroidism for current year (n=16) and the previous year Characteristics: THIS YEAR (% or mean) LAST YEAR Total hypothyroid patient population Subset of population with hyperthyroidism due to medication164 Gender (%) 4 (25%) male 12 (75%) female 1 (25%) male 3 (75%) female Age, years (mean ± std dev)46 (±14)44 (±12) Years since diagnosis (mean ± std dev)15 (± 22)14 (±24) ICD-9-CM code (%)16 (100%)4 (100%) Average l-thyroxine dose (mean ± std dev)38mcg (± 10mcg)45mcg (±18mcg) Months on current dose (mean ± std dev)15 (± 56)14 (±53) Months since most recent symptoms appeared (mean ± std dev)1.5 (± 0.04)3 (±4.5) Table 10.1

Cross-Sectional Survey of Patients with medication- related Hyperthyroidism for one year (n=16) Characteristics:TOTAL Gender (%)4 (25%) male 12 (75%) female Age, years (mean ± std dev)46 (±14) Years since diagnosis (mean ± std dev)18 (± 29) Average l-thyroxine dose (mean ± std dev)32mcg (± 16mcg) Months on current dose (mean ± std dev)18 (± 64) Months since most recent symptoms appeared (mean ± std dev)1 (± 0.34) Pharmacies used during past year (can list more than one) Rx corner 12 (75%) Chain Scripts 4 (25%) Clinic pharmacy 8 (50%) VA mail order 1 (7%) Brand name of medication Synthroid® 4 (25%) Levo-throid® 4 (25%) levo-thyroxine (GenX brand) 8 (50%) Usual number of days in prescription (mean ± std dev)30 (± 2) Self-reported compliance (mean days/ month took dose ± std dev) 28 (± 3) Medical Lab where T4 / TSH analyzedMML 16 (100%) Table 10.2

Sample of Case Report Data for five of the 16 clinic patients with medication-related hyperthyroidsim Characteristics:CFLACWHTHC GenderFFMFM Age Date of diagnosis02/198804/0811/199705/0402/09 Current l-thyroxine dose25mcg 50mcg25mcg Pharmacy filling last prescriptionRx Corner Brand of l-thyroxine last dispensedGenX Date last prescription filled prior to onset of hyperthyroidism symptoms Jan 29Feb 1Jan 24Jan 29Jan 25 Date hyperthyroidism symptoms appearedFeb 2Feb 5Jan 29Feb 4Jan 30 Table 10.3

Relative Risk from Cohort Study of Medication Errors Figure 10.9

Odds Ratios from Case-Control Study of Med Errors Figure 10.11