MB- DISEASE AND EPIDEMIOLOGY

EPIDEMIOLOGY

● The study of where and when diseases occur

and how they are transmitted in populations

Epidemiologists:

-Determine etiology of a disease

-identify spread of disease

-control disease

-make data of incidence of disease

John Snow

1848–1849

Mapped the occurrence of

Cholera in London

FATHER OF EPIDEMIOLOGY

Ignaz Semmelweis

1846–1848

Showed that handwashing decreased the incidence of peurperal sepsis

-was a doctor who showed that just washing hands shows spread of disease

Florence Nightingale

1858

Showed that improved sanitation decreased the incidence of epidemic typhus

-mapped that infectious disease was the leading cause of death

Pathology

the study of disease

Etiology

the cause of a disease

Pathogenesis

the development of

disease

Infection

invasion or colonization of

the body by pathogens

Disease

an abnormal state in which

the body is not performing normal

functions

Symptoms

changes in body function

that are felt by a patient as a result of

disease

-can’t be seen (internal)

Signs

changes in a body that can be

measured or observed as a result of

disease

(can be seen external)

Syndrome:

a specific group of signs

and symptoms that accompany a

disease

Communicable disease:

a disease that is

spread from one host to another

Contagious diseases:

diseases that are

easily and rapidly spread from one host to

another

Noncommunicable disease:

a disease that

is not spread from one host to another

eg. cancer, heart disease, diabetes

Incidence:

number of people who develop a

disease during a particular time period

Prevalence:

number of people who develop

a disease at a specified time, regardless of

when it first appeared

• Takes into account both old and new

cases

Sporadic disease:

disease that occurs only occasionally

-usually from a traveler

Endemic disease:

disease constantly present in a population

-usually always a certain level of that disease in that area

eg. Lyme disease, malaria

Epidemic disease:

disease acquired by

many people in a given area in a short time

eg. Ebola

Pandemic disease:

worldwide epidemic

eg. Covid-19 caused by SARS-CoV-2

Acute disease:

symptoms develop rapidly

but the disease lasts only a short time

Chronic disease:

symptoms develop slowly

Subacute disease:

intermediate between

acute and chronic

Latent disease:

Latent disease:

Herd immunity:

immunity in most of a

population

Local infection:

pathogens are limited to a

small area of the body

Systemic (generalized) infection:

an infection

throughout the body

Focal infection:

systemic infection that began

as a local infection

Bacteremia:

bacteria in the blood

Septicemia

also known as blood poisoning;

growth of bacteria in the blood

Sepsis:

toxic inflammatory condition arising

from the spread of microbes, especially

bacteria or their toxins, from a focus of

infection

Toxemia

toxins in the blood

Viremia:

viruses in the blood

Primary infection:

acute infection that

causes the initial illness

Secondary infection:

opportunistic infection

after a primary (predisposing) infection

Subclinical disease:

no noticeable signs or

symptoms (inapparent infection)

Predisposing Factors

Make the body more susceptible to disease

• Gender

• Inherited traits, such as the sickle cell gene

• Climate and weather

• Fatigue

• Age

• Lifestyle

• Nutrition

• Weight

• Chemotherapy

Incubation period:

interval between initial

infection and first signs and symptoms

Prodromal period:

short period after

incubation; early, mild symptoms

Period of illness:

disease is most severe

Period of decline:

signs and symptoms

subside

Period of convalescence:

body returns to

its prediseased state

Human Reservoirs: Carriers

may have inapparent infections or

latent diseases

• Typhoid Mary

Animal reservoirs: Zoonoses

are diseases transmitted from

animals to humans

• Rabies, Lyme Disease, Influenza, CoVid-19

Animal reservoirs: Nonliving reservoirs

Soil and water

• Tetanus, cholera

Direct contact transmission:

requires close

association between the infected and a

susceptible host

• Kissing, coughing, sex

Indirect contact transmission:

spreads to a host

by a nonliving object called a fomite

• Tissues, towels, diapers, utensils, money, syringes

Droplet transmission:

transmission via airborne

droplets less than 1 meter

• Cough, sneeze, laugh, talking

Transmission of Disease : Vehicle Transmission

Transmission by an inanimate reservoir

• Waterborne

• Usually untreated sewage

Foodborne

• Incompletely cooked, no or poor refrigeration, unsanitary

Airborne

• Droplet nuclei, dust, fungal spores

Vectors

Arthropods, especially fleas, ticks, and mosquitoes

Transmit disease by two general methods

Mechanical transmission:

arthropod carries pathogen on its body

• Household flies

Biological transmission:

pathogen reproduces

in the vector; transmitted via bites or feces

• mosquitoes, ticks, lice

nosocomial infections

Acquired while receiving treatment in a health

care facility

Affect 1 in 25 hospital patients in US!, 2 million affected per year

HAIs result from:

• Microorganisms in the hospital environment

• Weakened status of the host

• Chain of transmission in a hospital

Compromised host:

an individual whose resistance

to infection is impaired by disease, therapy, or

burns

Control of Healthcare-Associated

Infections

Reduce number of pathogens

• Handwashing

• Disinfecting tubs used to bathe patients

• Cleaning instruments scrupulously

• Using disposable bandages and

intubation

Emerging Infectious Diseases

Diseases that are new, increasing in

incidence, or showing a potential to

increase in the near future

Most are zoonotic, of viral origin, and

likely to be vector-borne

Contributing factors:

-Genetic recombination

-Evolution of new strains

-changes on weather

(CDC)

Collects and analyzes epidemiological

information in the United States

Morbidity

incidence of a specific

notifiable disease

Mortality

deaths from notifiable

diseases

Notifiable infectious diseases:

diseases in

which physicians are required to report

occurrence

Morbidity rate:

number of people affected in

relation to the total population in a given time

period

Mortality rate:

number of deaths from a disease

in relation to the population in a given time