lecture 1 of week 3 about public health introduction and more

Lecture on public health

1. PUBH115 PUBLIC HEALTH DR. AMINA RAZA KHAN [email protected]

2. Epidemiology Lecture 2 Week 2 2

3. Adapted from: Last JM, ed. A dictionary of epidemiology. 2 nd ed. Toronto, Canada: Oxford University Press; 1988. Epidemiology — Defined Study of the distribution and determinants of health-related states among specified populations and the application of that study to the control of health problems 3

4. Epidemiology Purposes in Public Health Practice Discover the agent, host, and environmental factors that affect health Determine the relative importance of causes of illness, disability, and death Identify those segments of the population that have the greatest risk from specific causes of ill health Evaluate the effectiveness of health programs and services in improving population health 4

5. Patterns of Disease Occurrence From the following information, epidemiologists can infer why a disease is occurring: Who is getting the disease? When did they get the disease? Where is the disease occurring? The ultimate goal is to use this knowledge to control and prevent the spread of disease.

6. Solving Health Problems Step 1 Data collection Solving health problems Assessment Hypothesis testing Action Step 2 Step 3 Step 4 Surveillance; determine time, place, and person Inference Determine how and why Intervention Step 1 - Step 2 Step 3 Step 4 6

7. Epidemic Surveillance Is a major line of defense in protecting the public against disease Important terms are: Endemic versus epidemic “Notifiable” diseases “Shoe leather epidemiology” System was created to control spread of known disease but also aids in recognizing new disease. Importance has increased with threat of bioterrorism and pandemics.

8. Outbreak Investigation establishing the existence of an outbreak preparing for fieldwork verifying the diagnosis defining and identifying cases using descriptive epidemiology developing hypotheses evaluating the hypotheses refining the hypotheses implementing control and prevention measures communicating findings Ten steps are involved in outbreak investigations, including 8

9. Outbreak Investigation — Steps 1 and 2 Fraser DW, Tsai, T, Orenstein W, et al. Legionnaires’ disease: description of an epidemic of pneumonia. New Engl J Med 1977;297 1189–97. Use data from data sources Step 1 — Establishing the existence of an outbreak Research the disease Gather supplies and equipment Arrange travel Step 2 — Preparing for field work 9

10. Outbreak Investigation — Steps 3 and 4 Fraser DW, Tsai, T, Orenstein W, et al. Legionnaires’ disease: description of an epidemic of pneumonia. New Engl J Med 1977;297 1189–97. Speak with patients Review laboratory findings and clinical test results Establish a case definition by using a standard set of criteria Step 3 — Verifying the diagnosis Step 4 — Defining and identifying cases 10

11. Outbreak Investigation — Step 5 Fraser DW, Tsai, T, Orenstein W, et al. Legionnaires’ disease: description of an epidemic of pneumonia. New Engl J Med 1977;297 1189–97. Step 5 — Using descriptive epidemiology Describe and orient the data 11

12. Outbreak Investigation — Steps 6, 7, and 8 Fraser DW, Tsai, T, Orenstein W, et al. Legionnaires’ disease: description of an epidemic of pneumonia. New Engl J Med 1977;297:1189–97. Step 6 — Develop a focused hypothesis Step 7 — Evaluate the hypothesis for validity Step 8 — Refine the hypothesis as needed 12

13. Outbreak Investigation — Steps 9 and 10 Fraser DW, Tsai, T, Orenstein W, et al. Legionnaires’ disease: description of an epidemic of pneumonia. New Engl J Med 1977;297:1189–97. Step 9 — Implement control and prevention measures Determine who needs to know Determine how information will be communicated Identify why the information needs to be communicated Step 10 — Communicate findings Control and prevent additional cases 13

14. Summary Outbreak Investigation Verify the diagnosis. Construct a working case definition. Find cases systematically. Apply active surveillance. Ask who, where, and when questions to describe the epidemic by person, place, and time. Consider the incubation period. Look for a common source of exposure.

15. John Snow and Cholera First example of use of epidemiology to study and control a disease was by Snow for cholera. London had Cholera epidemics in mid-1800s. Snow suspected an association with the water supply, the Thames River. He conducted a “natural experiment”: He questioned households where cholera death had occurred. Most deaths were associated with one water supply company. https://www.youtube.com/watch?v=VJ86D_DtyWg

16. Epidemiologic Principles and Methods Public Health PUBH115 16 Epidemiology is defined as “the study of the distribution and determinants of disease frequency in human populations.”

17. Step 1: Define the Disease Death is easy to determine. A death certificate states cause of death. A blood test or stool culture is needed to verify a diagnosis of certain diseases. Some diseases are hard to define. EMS and SARS Sometimes a definition changes as more is learned. AIDS Other health outcomes include injuries and risk factors.

18. Disease Frequency Count the number of people with a disease and relate that to the population at risk (PAR). PAR (denominator) may be the total population or exposed population, or one gender or age group. PAR often comes from a census. Two ways to measure frequency are: Incidence, the number of new cases Prevalence, the number of existing cases Incidence is used for studying causes of disease.

19. Distribution of Disease Who: Sex, age, occupation, race, and economic status When: Looks for disease frequency over time: Season, year (long-term trends), elapsed time since an exposure (epidemic curve) Where: Neighborhood (e.g., clusters), latitude (climate), urban vs. rural, national variations Looks at comparisons of disease frequency in different countries, states, counties, or other geographical divisions

20. Determinants of Disease Why is distribution as it is? We can make inferences from distribution. Epidemiologists usually speak of risk factors not causes.

21. Human Population Epidemiology studies human population, usually using observational rather than experimental methods. Biomedical approach uses animal models to investigate the causes of disease. Experiments conducted on animals can yield clear answers as to cause and effect. For ethical reasons, experiments cannot usually be done on humans.

22. Epidemiology Study Types Epidemiology study types Experimenta l Observationa l Descriptive Analytic 22

23. Descriptive and Analytic Epidemiology Descriptive epidemiology Analytic epidemiology When was the population affected? How was the population affected? Where was the population affected? Why was the population affected? Who was affected? 23

24. Kinds of Epidemiologic Studies Goal is to determine an association between an exposure and a disease or other health outcome. Studies may be prospective or retrospective. Intervention study Cohort study Case-control study

25. Data Sources and Collection Methods Source Method Example Individual persons Questionnaire Survey F oodborne illness outbreak CDC’s National Health and Nutrition Examination Survey Health data on U.S. residents Environment Samples from the environment (river water, soil) Sensors for environmental changes Collection of water from area streams — check for chemical pollutants Air-quality ratings Health care providers Notifications to health department if cases of certain diseases are observed Report cases of meningitis to health department Nonhealth–related sources (financial, legal) Sales records Court records Cigarette sales Intoxicated driver arrests 25

26. Intervention Study Epidemiologists do not perform the experiments. Closest thing to an experiment. Start with two groups: Experimental group (gets the intervention or exposure) Control group Watch them over time and compare outcomes. Experimenter chooses who is in which group. Two groups should be as similar as possible so that intervention is the only difference.

27. Cohort Study Are for situations when doing an intervention study would be unethical or too difficult. Considered the next most accurate Choose a large number of healthy people, collect data on their exposures, and track outcomes over time. The only difference from intervention is that people choose their own exposures.

28. Case-Control Study Faster and cheaper are the advantages. This is the least accurate approach. It is commonly done to follow up on a hypothesis generated by shoe leather epidemiology. Choose people who already have disease. Choose a healthy control group of individuals, as similar as possible to cases. Interview them all and ask for their previous exposures. Estimate the strength of the association between exposure and disease by calculating an odds ratio.

29. Problems with Studying Humans Intervention study problem: Subjects may not follow prescribed behavior throughout study period. Cohort study problem: Sometimes it is hard to isolate which of many factors are responsible for health differences. Case-control study problems: Control group may not be truly comparable. Errors may exist in reporting or recalls. For all studies, differential drop-outs are worrisome.