Chapter 1

Epidemiology:

the study of the distribution and determinants of disease frequency in human populations and the application of this study to control health problems

• descriptive

• analytic/ scientific

Epidemiology is based on what two fundamental assumptions?

1. human disease does not occur at random

2. factors or determinants can be identified by systematic investigation of populations or subgroups within populations

Human populations:

a group of people with a common characteristic such as residence, age, gender, group membership, etc

Disease frequency:

counting the number of cases of a disease in a population over a specific time period

Determinants:

factors that cause some people to get disease or factors that prevent in getting a disease

• exposures

Disease distribution:

the pattern of disease according to the characteristics of a person, place, and time

• who is getting sick

• where is it occurring

• how is it changing over time

Disease control:

the reduction or elimination of disease occurrence

• accomplished through epidemiology research and surveillance

Hypothesis:

a testable statement that tries to explain a set of observations and can be tentatively rejected (or not rejected) through scientific research

• project expected association between two or more measurable variables

• carry clear implications for testing stated relations

Historical Development of Epidemiology:

• spans 400 years

• progress slow and unsteady

• key figures

  • John Graunt

  • James Lind

  • William Furr

  • John Snow

Cholera:

swept into Europe in early 1800s, specifically London and Paris

• symptoms include

  • nausea, dizziness

  • violent vomiting and diarrhea

  • “Rice water” stools

  • death

  • cardiovascular collapse

What were the beliefs about transmission of Cholera?

believed to be person-to-person via respiratory system

• miasmas → mysterious vapors from swamps, cemeteries, cesspools

John Snow:

London physician to the poor who studied cholera outbreaks in the 1830s and saw it was transmitted by fecal contamination of drinking water

• reasoned it might be transmitted by water or food due to gastrointestinal symptoms

• conducted landmark series of studies

  • tested his hypothesis about mode of transmission

  • led to investigation

London Water Supply:

some families carried water from community pumps, but others got water from companies that pumped water from the Thames River via pipes

• snow compared rates of mortality from cholera based on water supply companies in subdistricts of London

What were the significance of John Snow’s endeavors?

based on observation and reason he proposed a new hypothesis for how cholera was transmitted → one of the first observational studies

• tested hypothesis by collecting data systematically and comparing groups of people

• established an association between certain drinking water and getting cholera

  • never found direct evidence

• argued for an intervention that prevented more cases

What is the cause of cholera?

bacterium, Vibrio cholera, which is transmitted by ingestion of water or food contaminated with sewage

What have been some Epidemiological Milestones?

Descriptive Epidemiology:

describe disease patterns; identify and count cases of disease in populations and conduct simple studies

• monitor public’s health

• evaluate success of intervention programs

• generate hypotheses about causes of disease

Analytic Epidemiology:

search for disease causes and preventions; compare groups and systematically determine if there is an association

• evaluate hypothesis about causes of disease

• evaluate success of intervention programs

Closer look at Descriptive Epidemiology:

main uses

• identify problems, trends, and high-risk groups

• public health planning: where to spend resources

• generate hypotheses for analytical epidemiology

questions asked

• what are the main diseases in a population?

• who is getting disease?

• how does it vary across place and time?

limitation: CANNOT identify the causes of disease

Is the following data of the Nile Virus considered an outbreak?

Yes

Is the following data of Tuberculosis considered an outbreak?

No

Closer look at Descriptive Studies (outbreak):

the occurrence of cases of an illness clearly in excess of what is normally expected

• endemic

• epidemic

• pandemic

What is the goal of public health?

focuses on preventing illness of the population and implementing solutions typically involving community-level interventions that control or prevent cause of problem

• assessing health status of population

• educational programs

Basic health research:

study disease in a laboratory setting by conducting experiments on cells, tissues, and animals in order to understand disease mechanisms or processes

• regulate all important aspects of the experimental conditions

• results are often difficult to extrapolate to real-life situations involving humans

Clinical health research:

focus research questions mainly on disease diagnosis, treatment, and prognosis in individual patients

• usually based on people who come to a medical care facility

• often unrepresentative of the full spectrum of disease in the population

Public health research:

study ways to prevent disease and promote health in the population at large

• mainly disease prevention not treatment

• units of community rather than individual

John Graunt:

summarized the patterns of mortality in 17th-century London and discovered the regularity of deaths and births

James Lind:

conducted one of the earliest experimental studies on the treatment of scurvy among sailors using sound experimental principles

• found that the consumption of oranges and lemons was the most effective remedy for scurvy in this population

William Farr:

pioneered many activities encompassed by modern epidemiology

• calculation of mortality rates using census data for denominators

• fair comparisons

Streptomycin Tuberculosis Trial:

one of the first modern experimental studies on the use of streptomycin to treat pulmonary tuberculosis

• used random assignment

• placement of restrictions on the type of patient eligible for the trial

• free of bias

• considered the ethical issues involved in conducting the trial

Doll and Hill Studies:

conducted groundbreaking studies on cigarette smoking and lung cancer in the 1950s

Framingham Study:

notable for bringing about a shift in focus from infectious to noninfectious diseases following World War II

• development of appropriate methods for measuring the major risk factors for coronary heart disease

• solving problems associated with measurements that vary over time

What are some of the current challenges of modern epidemiologists?

• air, water, and soil pollution

• global warming

• population growth

• poverty and social inequality

• civil unrest and violence