HLTH 421/521 ~ Epidemiology

1. HLTH 421/521 ~ Epidemiology New Mexico Highlands University 2013 Dr. Pete LeRoy 505.699.6067 cell 505.426.2233 office

2. Epidemiology The Study of the Distribution and Determinants of Diseases and Injuries in Human Populations

3. Epidemiology Terms • Epidemiology is the study of the distribution & determinants of health events in human populations – it uses biostatistical tools & methods to quantify the distribution & determinants of health events in groups of people rather than individuals • Epidemiology is known as the basic science of public & community health because it provides data for directing public health action

4. Endemic versus Epidemic • Heart disease in the U.S. is endemic…this means that over the years there has been a predictable number of occurrences each year… • If suddenly there was a dramatic increase in heart disease one year, an epidemic would be said to occur… • Epidemiologists would seek to explain this sudden “outbreak…”

5. Pandemic • Occasionally, an epidemic will spread over an entire continent, or, worldwide… • When this occurs, the epidemic is called a pandemic… • An example of a pandemic is AIDS which affects populations worldwide…

6. John Snow – Father of Epidemiology • Cholera epidemic in London in 1849… • John Snow, a physician, interviewed cholera victims and their families… • Hypothesized that the source of the cholera was a contaminated pump handle for a communal well… • To test his hypothesis, Snow removed the pump handle and forced the people who normally used that well to go to anther well… • Thirty years later, Louis Pasteur proposed his “germ theory” of disease causation.

7. Epidemiology • “the study of how diseases occur and distribute themselves in populations…” • Epidemiologists seek to explain how diseases occur in populations and generally become involved when an epidemic occurs… • An epidemic is any unexpected larger then usual number of diseases… • Epidemics are usually determined in light of Endemic rates…the usual number of cases over a determined period of time.

8. Epidemiology Terms • The epidemiologic triad = has three components: (a) an external agent, (b) a susceptible host, and (c) an environment that brings the host and the agent together • Agent = an infectious microorganism • Host factors = those that influence one’s exposure, susceptibility, or response to a causative agent • Environmental factors = generally include physiological factors such as geology, climate, and physical surroundings

9. Epidemiology Terms • The epidemiologic triad = has three components: (a) an external agent, (b) a susceptible host, and (c) an environment that brings the host and the agent together • Agent = an infectious microorganism • Host factors = those that influence one’s exposure, susceptibility, or response to a causative agent • Environmental factors = generally include physiological factors such as geology, climate, and physical surroundings

10. Communicable Disease Model Host Agent Environment All other factors that inhibit or promote disease transmission

11. Communicable Disease Model Agent The element that must be present in order for the diseases to occur

12. Communicable Disease Model Host Any susceptible organism invaded by an infectious agent

13. Chain of Infection A model to conceptualize the transmission of a communicable disease from its source to a susceptible host

14. Types of Diseases Examples Acute Diseases Communicable Noncommunicable Chronic Diseases Communicable Noncommunicable Common cold, pneumonia, mumps, measles, pertussis, typhoid fever, cholera Appendicitis, poisoning, trauma Tuberculosis, AIDS, Lyme disease, syphilis, rheumatic fever Diabetes, coronary heart disease, osteoarthritis, cirrhosis of the liver

15. Chain of Infection Portal of exit Pathogen Portal of entry New host Trans- mission Reservoir - Final link is a susceptible host

16. Causative Agents for Diseases and Injuries Biological Agents Chemical Agents Physical Agents Viruses Rickettsiae Bacteria Fungi Protozoa Metazoa Pesticides Food additives Pharmacologics Industrial chemicals Air pollutants Cigarette smoke Heat Light Radiation Noise Vibration Speeding objects

17. Epidemiology Terms • Infectivity = the proportion of exposed persons who become infected • Pathogenicity = the proportion of infected persons who develop clinical disease • Virulence = the proportion of persons with clinical disease who become severely ill or die

18. Epidemiology Terms • Chain of infection = transmission of disease occurs when the agent leaves its reservoir or host through a portal of exit, and is conveyed by some mode of transmission, and enters through an appropriate portal of entry to infect a susceptible host • Reservoirs include humans, animals and the environment

19. Epidemiology Terms • Two types of human reservoirs = (a) persons with asymptomatic disease & (b) carriers • Carrier = one without apparent disease who is nonetheless capable of transmitting the agent to others • Portal of exit = the path by which an agent leaves the source host

20. Epidemiology Terms • Modes of transmission = direct and indirect • Direct = (a) direct contact & (b) droplet spread • Indirect = (a) airborne, (b) vehicleborne, (c) vectorborne

21. Epidemiology Terms • Direct transmission = there is immediate transfer of the agent from a reservoir to a susceptible host by direct contact or droplet spread • Indirect transmission = an agent is carried from a reservoirs to a susceptible host by suspended air particles or by animate (vector) intermediaries

22. Epidemiology Terms • Data gathered in epidemiological studies are organized and summarized according to time, place, and person – these three characteristics are sometimes called epidemiologic variables • Time = disease rates change over time; through study, we know when to predict certain outbreaks of influenza, for example

23. Epidemiology Terms • Place = we describe a health event by place to gain insight into the geographical distribution of a problem • Person = we may use various characteristics such as age, race, sex, occupation, et cetera; this is accomplished in order to ascertain to a large degree who is at greatest risk of experiencing some undesirable health condition

24. Epidemiology Terms • The most commonly used statistical tool in epidemiology is a rate • Rates which describe the frequency of death in a population are mortality rates • Rates which describe the occurrence of disease in a population are morbidity rates

25. Rates • Epidemiologists are concerned with numbers…especially, number of cases… • A case is a person…number of cases refers to either number of deaths or illnesses… • Number of Cases, however, mean nothing unless we know about the number of people susceptible to the condition… • A Rate is the number of events (illnesses, deaths) in a given population over a period of time or, at some particular point in time.

26. Rates used for Comparison • Rates help us to know if there are more cases of lung cancer per capita in 2003 than there were in 1950…knowing numbers alone would tell us nothing unless we knew the population numbers for 2003 and 1950… • Rates help us to know if there are more suicides in N.Y. than Chicago for any given year but only if we have population numbers…

27. Epidemiology Terms • Four major types of epidemiological research study are: • Cross-sectional study = a “snapshot” study describes the prevalence of health events at a particular point in time • Case-control study = a “look back” in time • Cohort study = a “motion picture”, i. e., it follows groups of individuals through a period of time • Experimental study = these provide the strongest evidence possible of disease causation; key element is control

28. Levels of Prevention • Primary Prevention • The forestalling of the onset of illness or injury during the pre-pathogenesis period (before the disease process begins) • Secondary Prevention • The early diagnosis and prompt treatment of diseases before the disease becomes advanced and disability becomes severe • Tertiary Prevention • The retraining, reeducation, and rehabilitation of the patient who has already incurred disability