Multicausation disease model

Chapter 4

Epidemiology:

Prevention and Control

of Diseases and Health

Conditions

Introduction

• Diseases and other health conditions are classified

in several meaningful ways

• Classification can lead to prevention and control

strategies

Classification of Diseases and Health

Problems • In community health, diseases are usually

classified as:

• Acute or chronic (<3 or >3 months)

• Communicable or noncommunicable

Communicable versus

Noncommunicable Diseases

• Communicable (infectious) diseases – those diseases

for which biological agents or their products are the

cause and that are transmissible from one individual

to another

• Noncommunicable (noninfectious) diseases – those

illnesses that cannot be transmitted from one person

to another

• Identifying cause is difficult because many factors can

contribute

Acute versus Chronic Diseases and

Illnesses • Diseases classified by duration of symptoms

• Acute – diseases in which peak severity of

symptoms occurs and subsides within 3

months

• Can be communicable or noncommunicable

• Chronic – diseases or conditions in which

symptoms continue longer than 3 months

• Can be communicable or noncommunicable

Communicable Diseases

• Infectivity: ability of a biological agent to

enter and grow in the host

• Agent: cause of disease or health problem

• Host: susceptible person or organism invaded

by an infectious agent

• Environment: factors that inhibit or promote

disease transmission

• Pathogenicity: capability of a communicable

agent to cause disease in a susceptible host

Biological Agents of Disease

Communicable Disease Model

Chain of Infection

• Step-by-step model to conceptualize the

transmission of a communicable disease from

its source to a susceptible host

Chain of Infection

• Pathogen: disease causing agent (virus, bacterium,

etc.)

• Reservoir: favorable environment for infectious

agent to live and grow (human, animal, etc.)

• Portal of exit: path by which agent leaves host

Transmission: how pathogens are passed from

reservoir to next host

• Portal of entry: where agent enters susceptible host

New host: susceptible to new infection being

established

Chain of Infection

• Zoonoses – diseases for which the

reservoir resides in animal populations

• Anthroponoses – diseases for which

humans are the only known reservoir

Modes of Transmission

• Direct transmission – immediate transfer of

disease agent between infected and susceptible

individuals

• Touching, biting, kissing, sexual intercourse

• Indirect transmission – transmission involving

an intermediate step

• Airborne, vehicleborne, vectorborne, biological

• Vehicles – nonliving objects by which agents

are transferred to susceptible host

Chain of Infection Example

• Agent (cold virus), leaves reservoir (throat of infected

person), when host sneezes (portal of exit-nose and

mouth). Direct transmission (saliva droplets) enter

respiratory tract of susceptible host at close range

(portal of entry-mouth). New infection possibly

established. If one link is missing, chain is broken.

Noncommunicable Diseases

• Nation’s leading causes of death

• Heart disease, stroke, cancer

• Complex etiologies (causes)

• Multicausation disease model

• Host: inalterable, unique genetic endowment

• Personality, beliefs, behavioral choices: impact

host

• Complex environment: exposes host to risk

factors

Multicausation Disease Model

Noncommunicable Disease Problems

• Diseases of the heart and blood vessels

• Coronary heart disease

• Cerebrovascular disease (stroke)

• Malignant neoplasms (cancer)

• Chronic obstructive pulmonary disease

• Diabetes mellitus

• Chronic liver disease and cirrhosis

Prioritizing Prevention and Control

Efforts • Criteria used to judge importance of disease to

a community

• Number of people who will die from a disease

• Leading causes of death

• Number of years of potential life lost

• Captures issues affiliated with various groups

• Economic costs associated with disease

• Money spent at various levels of government;

ex: alcohol and other drugs

Prevention, Intervention, Control, and

Eradication of Diseases • Prevention: planning for and taking action to

prevent or forestall onset of disease or health

problem

• Intervention: effort to control disease in

progress; taking action during an event

• Control - Containment of a disease;

prevention and intervention measures

• Eradication: total elimination of disease from

human population

Levels of Prevention

• Primary prevention

• Forestall onset of illness or injury during

prepathogenesis period

• Secondary prevention

• Early diagnosis and prompt treatment before

disease becomes advanced and disability severe

• Tertiary prevention

• Aimed at rehabilitation following significant

pathogenesis; retrain, reeducate, rehabilitate

Primary Prevention of

Communicable Diseases

• Strategies at each link in chain of infection

• Individuals

• Hand washing, using condoms, properly

cooking food

• Communities

• Chlorinating water supply, inspecting

restaurants, immunization programs for all

citizens, vector control, solid waste disposal

• Individuals

• Self-diagnosis, self-treatment w/home remedies

• Antibiotics prescribed by a physician

• Communities

• Controlling or limiting extent of an epidemic

• Carefully maintaining records; investigating

cases

• Isolation, quarantine, disinfection

Secondary Prevention of

Communicable Diseases

• Individuals

• Recovery to full health after infection; return to

normal activity

• Communities

• Preventing recurrence of epidemics

• Removal, embalming, burial of dead

• Reapplication of primary and secondary

measures

Tertiary Prevention of

Communicable Diseases

Primary Prevention of

Noncommunicable Diseases • Individuals

• Education and knowledge about health and

disease prevention, eating properly, adequate

exercise, driving safely

• Communities

• Adequate food and energy supplies, efficient

community services, opportunities for

education, employment, and housing

Secondary Prevention of

Noncommunicable Diseases • Individuals

• Personal screenings (mammogram, pap test,

PSA test), regular medical and dental checkups,

pursuit of diagnosis and prompt treatment

• Communities

• Provision of mass screenings for chronic

diseases, case-finding measures, provision of

adequate health personnel, equipment, and

facilities

Tertiary Prevention of

Noncommunicable Diseases • Individuals

• Significant behavioral or lifestyle changes,

adherence to prescribed medications, following

rehabilitation requirements after surgery

• Communities

• Adequate emergency medical personnel and

services: hospitals, surgeons, nurses,

ambulance services

Discussion Questions

• Which components of the Multicausation

Disease Model can communities most

effectively impact?

• Which level of prevention is most important

for better community health outcomes and

why?

• Who plays a more significant role in

preventing diseases, individuals or

communities?

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