INTRO TO EPIDEMIOLOGY

Study of the distribution and determinants of health-related states

epidemiology

purposes of epidemiology:

• identify at-risk populations

• evaluate the effectiveness of health programs

solving health problems steps:

1. data collection - surveillance

2. assessment - inference

3. hypothesis testing - how and why

4. acton - intervention

Disease was due to ____ ______

evil spirits

Recovery was attributed to ____ ______

good spirits

________ as a form of punishment

disease

Control measures include offering ______ and _______ ___ _______

sacrifice and casting-out demons

Theories of disease causation:

1. filth theory

2. folklore theory

3. bacteriological theory

Associates disease with the physical environment

filth theory

Disease change with seasons, climate, temperature, overcrowding

filth theory

Diseases were due to poisonous substances and gases from the earth

filth theory

was the cause of fever

bad air

Building huge fires can purify the air

bad air

Programs to remove filth likewise put up to serve to advance community sanitation

bad air

____ confirmed Pasteur's previous claims

Koch

Disease is due to microscopic forms of life

bacteriological theory

Opened the concepts of isolation and quarantine

bacteriological theory

Measures to destroy and remove the bacteriological cause:

1. disinfection

2. fumigation

3. general cleanliness

explained the origins and spread of communicable disease

bacteriology

____ stated that four postulates should be met before a causal relationship

Koch

Henle-Koch’s postulates:

• Agent must be present in every case of disease.

• Agent must not appear in other diseases.

• Isolated agent must reproduce disease in a host.

• The agent must be recoverable from the infected host.

Disease results from the interaction of multiple ecologic factors within a dynamic system made up of an agent of disease, host and the environment

multiple causation

States that effects never depend on single isolated causes but rather develop as the result of chains of causation

the web

The host and agent are at the opposite ends of a

hypothetical lever

environment serves as the _______

fulcrum

external to the host and in which the agent may exist, survive, or originate

environment

living organism or inanimate matter in which an infectious agent normally lives and multiplies

reservoir

reservoir of infection

• physical environment

• animals or insects

• human

it has the infection and disease

cases

it has the infection but no disease

carriers

infectious diseases of animals that can cause disease when transmitted to humans

zoonotic diseases

examples of zoonotic diseases

• rabies

• plague

any element, substance, or force whether living or non-living, the presence or absence of which can initiate or perpetuate a disease process

agent

type of agents:

• non-living

• living

nutritive element excesses

cholesterol

nutritive elements deficiencies

vitamins, proteins

chemical agent poisons

• CO

• CCl4

• drugs

chemical agent allergens

ragweed, medication

physical agents

ionizing radiation

non-living agents:

1. physical and mechanical

2. chemicals (exogenous, endogenous)

3. nutrients (deficiency, excess)

extremes of temperature, light, electricity, physical trauma

physical and mechanical

poisonous chemicals

exogenous

accumulation of toxic products of metabolism

endogenous

anemia from iron deficiency

deficiency agents

obesity from overeating

excess agents

biological organism capable of causing disease

living agents

TB, shigellosis

bacteria

AIDS, hepatitis

virus and ricketssia

candidiasis, athlete’s foot

fungi

amoebiasis, giardiasis

protozoans

schistosomiasis, ascariasis

helminthes

Characteristics of Agents of Diseases

1. inherent

2. directly related to man

3. related to environment

include morphology, motility, presence or absence of capsule, spore or cyst forms

physical features

refers to the things needed by agent to survive

biologic requirements

Characteristics directly related to man

1. infectivity

2. pathogenicity

3. virulence

4. immunogenicity

the ability of an agent to invade and multiply in a host

infectivity

it is dependent on a number of factors including viability, portal of entry, susceptibility of the host, susceptible tissues and body defenses of the host

infectivity

ability to produce clinically apparent illness

pathogenicity

dependent on factors such as dosage, presence or absence of capsule, degree of toxigenicity, condition of the host

pathogenicity

severity of the reaction produced and measured in terms of fatality

virulence

infections ability to produce specific immunity

immunogenecity

Characteristics in relation to the environment

1. reservoir

2. sources of infection

3. modes of transmission

refer to the mechanisms by which an infectious agent is transported from reservoir to susceptible human host

modes of transmission

three modes of transmission:

1. contact

2. vehicle

3. vector

host is exposed to infectious agents by making contact with the agent or items contaminated with the pathogen

contact transmission

three types of contact transmission:

1. direct contact

2. indirect contact

3. droplet

There is no intermediary between infected and uninfected individuals

direct contact transmission

encompasses such things as touching, kissing, and sexual interactions

direct contact transmission

Diseases transmitted through direct contact:

1. hepatitis A

2. staphylococcal infection

3. STDs

seen in the transfer of respiratory diseases such as influenza and whooping cough

droplet transmission

It can occur through sneezing, coughing, and even laughing

droplet transmission

intermediates:

• tissues

• towels

• bedding

• contaminated needles

Nonliving intermediates that act as the agents of transmission by indirect contact

fomites

nvolves pathogens riding along on supposedly clean components

vehicle transmission

examples of vehicle:

• air

• food

• water

• blood

• blodily fluids

• drugs

it is a difficult vehicle to control

air

it uses air as a vehicle and can contain huge numbers of pathogens

dust

can also use air to travel from host to host

microbial and fungal spores

Pathogens are transmitted by carriers, usually arthropods

• fleas

• ticks

• flies

• lice

• mosquitoes

pathogens are on vector’s body parts and are passively brushed off and onto the host

mechanical vector

pathogens are within the vector and transmission to the host is through a bite

biological vector

goes through chain of events leading from inapparent infection to a clinical case of the disease

host

range of infection

inapparent to severe disease

end result of infection

• complete recovery

• permanent disability

• death

• chronicity

non-specific defense mechanisms

• skin

• tears

• saliva

• pH

Factor must be present for the disease to occur

necessary cause

Cause that inevitably initiates or produce an effect

sufficient cause

types of casual relationships:

1. necessary and sufficient

2. necessary but not sufficient

3. sufficient but not necessary

4. neither sufficient nor necessary

without the factor, disease never develops

necessary and sufficient

the factor in and of itself is not enough to cause disease

necessary but not sufficient

the factor alone can cause disease, but so can other factors in its absence

sufficient but not necessary

the factor cannot cause disease on its own, nor is it the only factor that can cause that disease

neither necessary nor sufficient

immunity of a group or a community

herd immunity

immunity of a high proportion of individual members

herd immunity

natural history of disease

1. stage of susceptibility

2. stage of subclinical disease

3. stage of clinical disease

4. stage of recovery, disability, or death

two phases of natural history of disease

• pre-pathogenesis

• pathogenesis

Through interaction of agent, host and environmental factors, agent finally reaches man

pre-pathogenesis

Includes the success invasion and establishment of the agent in the host

pathogenesis

From incubation period to production of detectable evidence of the disease process

pathogenesis

at risk to acquire the infection and/or amenable to get exposed to and be harmed by a health determinant

stage of susceptibility