Public Health Case Study Mark Wathen Is This Really Okay for Me?A Public Health Statistical Analysis CDC’s 2005 Science Ambassador Program
Case Study Outline • Public Health • Surveillance • Epidemiological Studies • Calculations • Prevalence • Incidence • Risk Ratio • Prevention
Public Health • Is the science and art of preventing disease, prolonging life, and promoting health through the organized efforts of society including • Monitoring disease and other health-related conditions (surveillance); and • Identifying and quantifying important trends (epidemiology).
Surveillance • Is the monitoring of the occurrence of a disease or other health-related condition. • Active surveillance • Actively searching for people with a disease or condition. • Passive surveillance • Dependent on reporting from external sources.
Epidemiology • The study of the distribution, determinants, and deterrents of disease or other health-related conditions. • Distribution is the frequency and patterns in terms of person, place, and time (who, where, and when). • Determinants are factors that cause or contribute to a disease or condition. • Deterrents are factors that prevent or reduce the chance of developing a disease or condition.
Prevalence = Number of people affected ______________________________________ total population Prevalence • The proportion of a population that has a disease or health-related condition during a specific time.
Case Study • February 2004. • School nurse reported 39 cases of the flu in the high school. • Age of students 14–18 years • Total of 780 students in the school. • What was the prevalence of the flu for this high school?
Prevalence = Number of people affected ______________________ total population Prevalence = 39 students with flu _____________________ 780 total students Prevalence = 5 out of every 100 students had the flu. Can also be said 5% of students had the flu. Prevalence Calculation • Report who, where, and when. • Population: Students aged 14–18 • Place: High school • Time: February 2004
Case Study—Continued • Results 5 out of 100 students had the flu. • Monitor the situation during the month of March (2004). • 9 new cases of flu within the school. • Calculate the incidence during this time period.
Incidence • The rate at which new disease or health-related condition occurs in a population. Incidence = Number of newly affected people ___________________________________ population at risk Incidence = 9 new cases of flu ___________________ (780 – 39) population at risk Incidence = 12 out of 1,000 students had the flu at the high school
Case—Study Continued • Results—12 out of 1,000 students had the flu. • What is the cause? • A teacher mentioned seeing students coughing and sneezing around the candy machine. • The nurse investigated to see if there was any correlation between the candy machine and having the flu.
Case Study—Continued • The nurse monitored 200 students over a 1-month period. • 120 used the candy machine. • 12 cases of flu occurred in this group. • 5 cases of flu appeared in the group that didn’tuse the candy machine. • So was there a risk in using the candy machine?
Prevalence Ratio • Ratio of prevalence of disease in the exposed group divided by the prevalence of disease in the unexposed group.
Prevalence Ratio = A / (A+B) _______ C / (C+D) Prevalence Ratio 22 Table
Prevalence Ratio = 12 / (120) = 1.6 _______ 5 / (80) Prevalence Ratio 22 Table
Analysis of Prevalence Ratio • If value >1, then exposure is producing outcome. • If value =1, no connection between exposure and outcome. • If value <1, exposure is prohibiting the outcome. • In the case study, the prevalence ratio was 1.6. Therefore, students using the candy machine were 1.6 times as likely to get the flu as students not using the candy machine.
Prevention • The final step of public health is prevention. • If you were the school nurse, what prevention program would you develop for your school?
Summary • Pubic health is the science and art of preventing disease, prolonging life, and promoting health through the organized efforts of society. • There are three parts to public health: • Surveillance, which monitors diseases and health-related conditions. • Epidemiology, which identifies and quantifies trends (prevalence, incidence, and risk ratio). • Prevention, which includes programs that inform and educate the population at risk.
References • “Public Health Measurement and Research Design” PowerPoint presentation by Alison Nair, CDC Ambassador Program, June 2004. • Oleckno, W.A. Essential Epidemiology: Principles and Applications. Waveland Press, Inc., Long Grove, Illinois, 2002.