SPH 596 Epidemiology Midterm 1

Greek derivations for epidemioloGy (3x)

Demos, epi, -logy

• demos =

• Epi =

• Logy =

• demos = people/population

• Epi = prefix for upon or on

• Logy = denotes field of study

T/f: epidemiology is The study of the distribution and determinants of the health of individuals and populations.

t

epidemiology definition

the study of how disease is distributed in populations and the factors that influence of determine this distribution

Epidemiology: The study of the distribution and determinants of health-related states or events in __ populations and the application of this study to control health problems.

specified

__is one of the foundational disciplines underlying public health. (Gordis)

Epidemiology

Epidemiology is the basic science of disease __ and plays major roles in developing and evaluating public policy relating to health and to social and legal issues

prevention

Epidemic: The occurrence in a community or region of cases of an illness, specific health-related behavior, or other health-related events clearly in excess of normal expectancy. (WHO)

Definition is not restricted to —— and —— diseases

Pathogens, infectious

The occurrence in a community or region of cases of an illness, specific health-related behavior, or other health-related events clearly in excess of normal expectancy

epidemic

An outbreak of a new pathogen that spreads easily from person to

person across multiple countries or continents and affects a large number of

people.

pandemic

pandemic: An outbreak of a new pathogen that spreads easily from person to

person across multiple __ or _ and affects a large number of

people.

countries, continents

3 criteria for pandemic (GHI)

• Widespread geographic spread:

• Sustained human-to-human transmission:

• Significant impact:

(pandemic criteria) - The disease has reached multiple countries and continents, affecting a large portion of the world population.

Widespread geographic spread:

objectives of epidemiology

1. identify the etiology of cause of a disease and its relevant risk factors

2. determine the extent of disease found in the community

3. study the natural history and prognosis of disease

4. evaluate existing and newly developed modes of health care delivery

5. provide the foundation for developing public policy relating to environmental problems, genetic issues, and other social and behavioural considerations

leading cause of death in 1900

pneumonia

influenza

tuberculosis

diarrhea

heart disease

cerebrovascular

leading cause of death 2015

cancer

heart disease

cerebrovascular

chronic lower resp diseases

injuries

epidemiological transition

The change from mainly infectious disease, still common in LMIC, to the degenerative chronic diseases, which have become the main cause of death in HICs.

increased remaining years of life at birth

due to decreased infant mortality and decreased childhood diseases

epidemiology

study of the frequency and pattern of health events/health states in a population

basic science of public health

distribution

descriptive epidemiology

ex: number of health events and relationship of that number to the size of the population

pattern changes by time, place, and person

determinants

analytic epidemiology

why and how

causes and risk factors (demographics, genetics, behaviours)

health related states/events

-communicable disease

-chronic disease

-injuries (birth defects, occupational/environmental health)

-health related quality of life (exercise, nutrition, health behaviours related to well-being)

specified populations

focused on the collective health of people in a community or population

application of knowledge

use of scientific methods of descriptive and analytic epidemiology as well as experience, judgement, and understanding of local conditions in diagnosing the health of a community and proposing appropriate, practical, and acceptable public health interventions to control and prevent disease in the community

types of epidemiology

descriptive

analytic

400 BC

hippocrates suggested that disease might be influenced by environment and behavior

1662

john gaunt developed the first mortality table associating births and deaths with age, sex, other factors. Also kept a record of causes of death. These causes of death included "apoplexy", "falling sickness", headache", and "frightened". First to develop Life Tables.

1800

william farr collected vital statistics, assembled, evaluated, and reported this data to health authorities.

promoted the idea that cause of disease could be multifactoral; developed a classification system for diseases and so on.

1854

john snow, father of epidemiology, studied cholera

cholera epidemic

first appeared in UK in 1830s, then again in 1848-49 and 1853-55

cholera infection

oral entry into the body, bacteria colonize small intestine, leads to nausea, diarrhea, muscle cramps, dehydration, shock

miasma

theory proposed by Edwin Chadwick

1848-49

miasma theory

epidemics like cholera were caused by effluvia from putrefying animal matter and exhalations of fever victims, most readily identified by the putrid odors

John Snow

had clinical experience, observed symptoms of cholera and also spread across nations

was an early contagionist

spread of cholera

india -> russia -> western europe -> england -> USA -> central america -> south america

Snow's theory

- epidemics follow routes of commerce

- agent is free living that multiplies within host

- transmission is water borne, spread from feces, ingested orally

cholera pathophysiology

diarrhea -> dehydration -> electrolyte imbalance -> seizures/coma -> death

3 epidemiological methods used by Snow

- ecological analysis

- cohort analysis

- case control

Snow's hypothesis

-GI disease, likely causal agent is ingested

-diarrhea most prominent symptom so causal agent likely left body this way

-diarrhea contaminates rivers and therefore drinking water

-spread of cholera

ecological studies

studies rates by regions (not on individual factors)

weakest form of epidemiological evidence (often first step)

snow's ecological analysis

looked at cholera mortality and water source by neighbourhood

noted high rates in communities served by Southwark Co and low rates in communities served by Lambeth Co

cohort studies

compare rates in exposed and non-exposed individuals

snow's cohort analysis

Use of Southwark Co water increased risk of cholera

determined that Southwark Co derived its water from fecal contaminated downstream sources

case control studies

compare people with disease (case) to those without disease (controls)

snow's case control results

61 cases used water from Broad St pump

6 did not use Broad St pump

6 were unsure where their water was from

non-cases much less likely to used Broad st. pump

Richard Doll

studied rising rates of lung cancer in UK

smoking and cancer

Doll interviewed 700 lung cancer patients, initially thought road tar was responsible

found that smoking was much more common in cancer patients

reduced life expectancy by 10 years compared to non-smokers

Progression of Epidemiological Reasoning

1. observation that factor seems to influence disease occurrence (arises from clinical practice, lace research, examination of disease patterns by person, place, time, prior studies etc)

2. formulate specific hypothesis/research question

3. conduct study to determine relationship between exposure and disease. consider chance, bias, and confounding variables when interpreting results

4. determine if observed association may be causal. other research, strength of association, time directionality

two perspectives

individual and population

population perspective

emphasized by epidemiology

focuses on disorders (mass disease), exposures, casual mechanisms in people as a group

community diagnosis - surveillance, descriptive data, surveys, analytic studies, intervention via health care system or policy

individual perspective

focuses on health, risk factors, exposures, and causal mechanisms in people as individuals

diagnosis - complaint, history, physical exam, lab tests

treatment derived from biomedical/psychological understanding of etiology

populations

dynamic, diverse, heterogenous

population characteristics

size/density

age

sex

geographical distribution

ethnicity

education

economic resource

population events

birth

marriage

migration

aging

death

descriptive epidemiology

describe patterns of disease by person, place, and time (WHO, WHERE, WHEN)

person variables

age

sex

race/ethnicity

socioeconomic status

occupation

education

religion

martial status

health status

immunization status

lifestyle practices

environmental exposures

epidemiologic transition

shift from acute and contagious disease to chronic and non-contagious disease

also decreased mortality, decreased fertility, aging of the population, shifts in morbidity to older age groups

triad of disease

host, environment, agent

vector in the center

host

must be susceptible, genetically, nutritionally, immunologically or socially

environment

promotes the exposure (geographic location for malaria)

vector

carries the agent (mosquito)

agent

causes the disease (spores, bacteria, virus, poison)

host factors in disease

age

gender

occupation

genetics

immunity

behavior

agent factors in disease

biologic

chemical

mechanical

nutritional

environment factors in disease

latitude

altitude

socioeconomic

water supply

food

pollution

radiation

modes of disease transmission

direct

indirect

direct transmission

person to person (STDs)

indirect transmission

-common vehicle (air, water) - single, multiple, or continuous exposure

-vector (car, mosquito)

endemic

habitual presence of a disease in a geographic area or "usual" occurrence of disease

unlimited in time but limited to place (CVD, obesity)

epidemic

occurrence of excess illness in area

limited in time and place (measles)

pandemic

epidemic crossing borders

limited in time but unlimited in place (covid, flu)

levels of prevention

primary

secondary

tertiary

primary prevention

to prevent disease before it develops so as to maintain health (smoking prevention, condom use)

secondary prevention

to diagnose and treat disease in its early stages so as to restore or improve health (pap test, blood pressure screening)

tertiary prevention

reduce complications of disease and improve functioning and quality of life where possible (hospice programs)

epidemiology and prevention

- population based prevention programs (targets everyone) must be inexpensive and often has a behavioral risk factor

- high risk subgroup (targets those at risk) can be more costly and often implies or requires clinical action (drinking and driving education focused at male drivers)

foreground questions

better for research

more likely to get completed

more likely to come up with a clear message for clinical practice/public health

more likely to help reader to rapidly assess if research is relevant

more likely to identify questions for the future

4 parts of a focused question

P - who is the patient

I/E - intervention or exposure

C - comparison group

O - outcome or endpoint

P (PICO)

patient, population, problem

(disease or condition, stage, severity, demographic characteristics)

I (PICO)

Intervention/exposure

(type of intervention or exposure, dose, duration, timing, route)

C (PICO)

comparison

(absence of risk or treatment, placebo or alternative therapy)

O (PICO)

outcome

(risk or protective, dichotomous or continuous, mortality, morbidity, quality of life etc)

study designs

RCTs

cohort

case control

cross sectional

etc

Abstracts

contain

- study design

- exposure

- outcome

- population

- PICO

descriptive study

- describes the distribution (patterns) of disease by person, place, and time (patterns of occurrence of health states)

- no prior hypothesis about exposure-outcome relationships

-looking for associations, not causal factors

- cannot infer causation

association and causation

does not mean causation

things are correlated but one does not cause the other

temporality and causation

to infer causation, have to make sure the exposure occurred before the outcome

types of descriptive studies

- case report/case series

- ecological study/correlational

- cross sectional

case report

descriptive

in depth, textual description of a single patient

case series

descriptive

textual or statistical analysis of cases (only those who are ill - no comparison)

goals of case report/series

- describe something unusual to alert others

- generate hypotheses for further studies

pros of case studies

fast

inexpensive

identification of new diseases, old diseases on new population, new exposures, can generate hypotheses for later research

cons of case studies

cases are not randomly selected, no comparison population (cannot determine association or quantify it)

- can only generate hypothesis, no results

ecological study

- compares groups, not individuals

- unit of analysis is the group (outcome or exposure) no individual data (summary exposure/outcome)

- cross sectional or longitudinal

-full or partial

types of ecological studies

cross sectional

longitudinal

pros of ecological

- fast and inexpensive

- generally uses previously published data

- can be useful for looking at something that is pervasive in some regions and not in others

cons of ecological

- can only generate hypotheses

- imprecise measures of association due to wide variability in summary exposure methods

- confounders

- temporal sequence

- ecological fallacy

ecological fallacy

bias that may occur because an association observed between variables on an aggregate level does not necessarily represent the association that exists at an individual level

(happens when you assume that the association that you see on a population level is occurring to the individuals in the population)

cross sectional study

- snapshot of disease/health/characteristics at one point in time

- random sample of individuals or all individuals in a given population at a given time

(ex: census)

measure of association = prevalence

sample of population is surveyed/interviewed/examined

outcome and exposure status is determined at the same time

(temporal sequence)

design of cross sectional (analytic)

- hypothesis about exposure (factors of interest) and outcome relationship formulated

- target population is determined

- sample selected (probability)

- exposure and outcome status are determined

- data analyzed and interpreted