BIOL 251 - Ch. 16 Study Points

Epidemiology

Study of the distribution and causes of disease in populations and how they are transmitted

Etiology

Study of causes of disease

Morbidity

State of being diseased

Morbidity rate

Number of diseased individuals out of a standard number of individuals in the population

Mortality

Overall death rate in population

Attack rate

Percentage of people who become ill in population after exposure to infectious agent

Reflects infectious dose, immune status of population

Incidence

Number of new cases/time/population

Measure of risk of an individual contracting a disease

Prevalence

Total number of cases at any time or for a specific period in a given population

Reflects overall impact of disease on society

Includes old and new cases, as well as duration of disease

What do epidemiologists do?

Collect and compile data about sources of disease and risk factors

Design strategies to prevent/predict spread of disease

Many daily habits based on epidemiology

Endemic

Constantly present in the population

Epidemic

Unusually large number of cases

Outbreak

Group of high number of cases at specific time and population

Pandemic

Global

Ex) AIDS, Covid-19

Fomites

Nonliving objects that facilitate the indirect transmission of pathogens

Chain of infection

Knowing chain for a given disease allows determination of where the chain can be broken

Reservoir of infectious agent → portal of exit → transmission → portal of entry → susceptible host

Reservoir of infection

Natural habitat of pathogen

Where pathogen normally resides

In or on animals, humans, or environment

Reservoir of infection (human)

Pathogen is easier to control if humans are only reservoir

Symptomatic infection

Clear sign of infection

Disease may be spread before symptoms appear or after they go away

Asymptomatic infection

Harder to identify - no signs/symptoms

Can spread to others before infection is known

Active carrier

Person is infected and spreads disease

Passive carrier

Person is not infected and spreads disease

Reservoir of infection (animal)

Difficult to control in wild animals

Zoonoses - animals → humans

Reservoir of infection (environment)

Food, water

Sometimes difficult or impossible to eliminate

Portal of exit

Body surface or orifice

Exit route for pathogen

Ex) intestinal tract, respiratory tract, skin, genitals, Vibrio cholerae exit thru feces

Vertical transmission

Pregnant woman to fetus or mother to infant during childbirth, breast feeding

Horizontal transmission

Person to person via air, physical contact, ingestion of food or water, or vector

Direct contact transmission

Touch to touch

Easiest when infection dose is low

Indirect contact transmission

Involves fomites that become contaminated by
pathogens from an infected individual or reservoir

Can be transmitted thru airborne ways

Vehicle transmission

Transmitted by objects, food, water, air (fomites)

Mechanical vector

Carries microbe on its body from one location to
another

Animal itself is not infected

Biological vector

Participates in life cycle of pathogen

Animal is infected

Portal of entry

Body surface or orifice

Entry route for pathogen

Factors influencing the epidemiology of
disease

Virulence

Dosage

Incubation period

Virulence factors

Factors that allow pathogen to attach to host cell, avoid immune defenses, damage host

Dosage

Minimum number of pathogens required to produce symptoms
If few cells enter, immune system may eliminate organism before symptoms appear

Incubation period

Influences extent of spread

Long incubation period can allow extensive spread before first symptoms appear

Population characteristics that influence
epidemiology of disease

Immunity

General health

Age

Gender

Religious or cultural practices

Genetic background

What type of studies do epidemiologists carry out?

Observational and experimental

Observational study

Measure associations between disease
occurrence and possible causative agents

Descriptive and analytical

Descriptive study

Type of observational study

Define characteristics of disease outbreak

Person, place, time

Analytical study

Type of observational study

Evaluates hypothesies to determine risk factors
relevant to spread of disease

Experimental studies

Often used to test effectiveness of a specific
treatment

CDC

National public health agency of US

Provides support for infectious disease
laboratories in the US

Collects data on disease of public health
importance

Publishes the weekly MMWR

Conducts research related to infectious diseases

Provides personnel for support in disease outbreak situations

Provides education for personnel dealing in infectious disease situations

Can send teams worldwide to assist with identifying and controlling epidemic

WHO

Agency of the UN responsible for global public health

Provide worldwide guidance in field of health

Set global standards for health

Cooperatively strengthen national health programs

Develop and transfer appropriate health technology

Notifiable diseases

Disease that a physician is required to report to the CDC

Emerging diseases

Diseases that are novel or have recently increased
in incidence

Ex) MERS, Ebola, Zika, SARS-CoV-2

Reemerging diseases

Diseases that increases in frequency after a period of decline

Prevention strategies may no longer be effective

Changing conditions (climate change)

Microbial mutation

Healthcare-associated infections (HAIs)

Acquired while receiving treatment in a healthcare setting such as a hospital, therapy center, urgent care facility, or long-term care residence

An infection a patient was not admitted to
the hospital for

One of top 10 causes of death in United States

Hospital-acquired nosocomial infections affect up to 5% of patients

Most common nosocomial diseases

Pneumonia

UTIs

Bloodstream infections