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126 Cards in this Set

  • Front
  • Back
Epidemiology is the study of the
distribution and determinants of health-related phenomenon in a population.
The field of science concerned with the circumstances under which diseases occur.
Factors under investigation in epidemiology:
1. incidence (morbidity rate)
2. Prevention and control of infectious and noninfectious diseases
3. Effects of diseaseson opopulation and individuals within a population
This type of disease occurs irregularly and only occasionally in a population (ex. Typhoid fever)
Sporadic Disease
This type of disease occurs at irregular intervals but at low levels (ex. common cold, rhinovirus)
Endemic disease
This type of disease is when occurrence frequency rises, but not to epidemic proportions. (ex. common cold in the winter months).
Hyperendemic disease
Sharp increase in the incidence above the predicted/expected level
Natural location of the organism, can be animate or inanimate
(ex. dogs- rabies, malaria-humans)
A disease that can be transmitted from one human to another or from animals to humans.
Communicable disease
Many diseases, but not all, are ________
(ex. Measles is, but head colds are not).
The immediate location from which infectious agent has been transmitted.
(ex. Hep. C - transfusion, blood products)
Hosts that harbor a pathogen without clinical symptoms and are capable of transmitting the infectious agent (sometimes unknowingly).
A short carrier state is known as
A long-term carrier state
Chronic carrier
Carrier state may also occur during which two periods?
Incubation period
Covalescent period
The period before symptoms appear
incubation period
The period of recovery
convalescent period
A biological or inanimate source that contributes to the transmission of an infectious agent from one host to another. (e. anthropods, ticks - Lyme disease)
Deals with animal diseases affecting animal populations.
Moderate incidence of epizootology
Rapid increase of epizootology
Wide spread of incidence in epizootology
If it is transferable to humans in epizootology
A type of communicable disease that is transmissible from a vertebrate animal to man. Normally it is a disease of animals.
Examples of zoonosis
Rabies, anthrax, lyme disease, hantavirus
What causes an infectious disease?
A microorganism.
Microorganisms may be a...
bacteria, virus, or fungus.
Risk factors for increasing emerging infectious diseases:
drug resistance, preterm babies, immunosuppression, floods, droughts, deforestation
What are the three conditions required for infection to spread?
1. one person mustbe infected with a microorganism
2. The other person must be susceptible to infection with that microorganism
3. The microorganism must be able to leave the body of the infected person and enter the body of susceptible person.
A microorganism, chemical, nutritive, element or physical factor whose presence or absence is essential for a particular disease or condition to occur.
Types of agents
Bacteria, protozoa, parasite
Some host factors include
1. Age, sex, ethnic group, nutritional status, socioeconomic status
2. Personal behaviors, smoking drinking diet sexual practices, exercise.
3. Immunization status: vaccinated or unvaccinated
The two goals of the epidemiologist are to
control the spread or dissemination
eliminate etiological agent
Surveillance and data collection for control
calculation of morbidity and mortality rates
case studies
field studies
Observable or measurable change in body function.
ex. diarrhea, rash fever, vomiting
ex. pain, appetite loss, lethargy, depression
A set of sings and symptoms that is characteristic of a disease
Disease syndrome
The interval between the time of contact and/or entry of the agent and onset of illness.
The time required for the multiplication of microorganisms within the host up to a threshold where the parasitic population is large enough to produce symptoms.
Incubation period.
Different incubation periods have variable _____ and are present prior to _________.
development of signs and symptoms
The beginning of signs and symptoms, often infectious/contagious, innate immune response "kick in" (first line of defenses).
Prodromal Stage
Most severe phase, clear evidence of signs and symptoms, acquired immune responses begin.
Illness stage
Humoral immune responses:
antibodies and conplement
Cell-mediated responses:
T cells instruct destruction of infected cells of destruction o intracellular bacteria.
Alleviation of signs and symptoms, recover/coalescence
Decline stage
The Natural History of Disease
Pre-clinical phase (incubation period)
Clinical phase: The person may become contagious before the onset of symptoms.
1. infection
2. Disease could be detected through testing/screening
3. Symptoms of disease develop
4. Symptoms resolve or the infected person dies.
Shorter incubation periods, upper gastrointestinal symptoms
longer incubation periods, typically lower gastrointestinal symptoms
Staphylococcus occurs between the time periods of
- and - hrs.
The symptoms of this are:
There is no significant fever, but the body temperature often
This is an example of an ______
1/2 hr to 8 hours, usually 2-4
cause: nausea, diarrhea, cramps, vomiting,
temp often drops
occurs between - hrs.
causes _______ with cramping, diarrhea, abdominal tenderness, vomiting, and fever.
This is an _____
6-72 but usually 12-36
Factors that play roles in the incubation period of a disease
dosage of the infectious agent
portal of entry
immune response of the host
Kissing, skin to skin contact and sexual intercourse are all examples of
(Also, plant or soil harboring infectious agents).
direct contact
Spray by short range aerosol, large droplets from coughing sneezing, talking, or singing
Droplet spread
The two forms of direct transmission are
droplet spread and diect contact
The three forms of indirect transmission are
air borne
vehicle borne
vector borne
Microbes, particles of droplet nuclei and dust suspend in the air
air borne
food, water, blood, tissues, organs and fomites
vehicle borne
disease transmission by a non-vertebrate host
vector borne
Inanimate objects capable of transferring infectious material
Bedding, toys, doorknobs, combs, clothing, drinking glasses, cooking utensils, pencils, straws, or surgical instruments are examples of
In vector borne transmission, an agent is carried by
a live non-human carrier (vector).
Most vectors are ________ (insects) such as mosquitoes, flies, ticks, or fleas, but they may be animals.
Vector-borne transmission may be _____ and/or _____.
mechanical, biological.
in Mechanical Vector borne Transmission the vector is contaminated through
mechanical means
There is no multiplication of the agent within
the vector
Vector borne diseases include
malaria, yellow fever, plague, typhus
background cases; expected number of cases
excess number of cases in a localized area
excess number of cases worldwide
Sharp increase to a peak, then rapid resolution.
Associated with common contaminated source
-food poisoning (food)
-legionnaire's disease
Common source epidemic
Extended rise with a gradual resolution
frequently observed with one individual = the source
-gradual dissemination, all susceptible individuals succumb
# of susceptible individuals eventually decreases due to acquired immunity.
-agent loses the ability to disseminate through the population.
propagated epidemic
Resistance a population acquires as a whole to infectious disease
Herd Immunity
The number of individuals that must be immune to prevent an epidemic outbreak of a disease is a function of
infectivity of the disease
duration of the disease
Proportion of susceptible individuals in the population
When 70% of the individuals in a population are immune, the propagation from individual to individual is not sustained and
epidemics do not occur.
The decreased possibility of a group or communityyu developing an epidemic because there is a specific level of immunity or resistance to that disease in the population
Herd immunity
opportunity for contact and transmission decreases as the number of immune individuals
susceptible individuals benefit from an indirect
immunity. (not self-made immunity)
occurs when there are more cases than you'd expect in a given area or among a given population in a specific period of time.
Steps to investigating an outbreak
1. Verify the outbreak
2. Plot tan epidemic curve
3. Calculate attack rates
4. Determine the source of the outbreak
5. Recommend and implement control measures
Establish a case definition
-who (person)
-what (symptoms)
-where (place)
-when (time)

identify, confirm, and quantify cases
determine if there's more cases than expected.
Verify the outbreak
First person that is sick
index case
people who get sick from being directly exposed to the agent
measured by attack rate
primary case
people who get sick from being exposed to a primary case
measured by secondary attack rate
secondary case
To plot an epidemic curve, graph the _____
x-axis =
y-axis =
interpret the _____
describe the pattern, determine the incubation period and perhaps....
Examine .....
time of onset
# of cases
the mode of transmission
The most common type of food-borne outbreak is in ....
this is for a large population with a short....
easier to identify the ......
example: bad potato salad at a picnic
point source transmission
short exposure period
incubation period
Several peaks of cases
difficult to characterize the
-ex. refrigeration temperature is off all week in a reastaurant
continueing source transmission
incubation period
When the cases start slowly, incubation period is estimated by the time between first case and the peak of cases, cases taper off slowly, example: west nile
Vector borne diseases
When calculating _______
it is an incidence rate, expressed as a percentage, calculated for different exposures or settings
Calculate Attack Rates
Attack rate =
# ill / ill + well (100)
To calculate RR -
compare attack rate for exposed vs. unexposed
Secondary attack rate =
total number of cases -initial cases / number of susceptible persons in the group - initial case (s)
A secondary attack rate is used to estimate the spread of
disease in a family, household, dorm, or other group environment
A secondary attack rate measures the
infectivity of the agent and the effects of prevention
Identify the most likely cause and investigate the source to prevent future outbreaks
determine the source of the epidemic
if there is no obviosu commonality, plot the geographic distribution of cases by
residence/work/school/locaion/ and seek exposures.
Control the present outbreak
prevent future similar outbreaks
recommend control meausre
A vast majority of outbreaks are
an incident in which (1) two or more persons experience a similar illness after
(2) epidemiological analysis implicates the
the investigation of a common good
food as the source of the illness
The three types of foodborne contamination
glass, metal fragments, sticks, dirt, bones, etc.
physical contamination
pesticides, cleaning compounds, poisonous metals, additives and preservatives
chemical contamination
bacteria, viruses, fungi, yeast, mold, parasites, poisonous fish and plants, insects and rodents
biological contamination
Major reasons for food-borne illness
foods are cooled or reheated improperly
improper holding temperatures
food handlers are infected
poor hygeine
incubation period of:
2-4 hours
staphylococcus aureus
cooked ham, meat, eggs, sauces, and gravies
12 hours
clostridium perfringes
cooked meat, gravy
12-36 hrs.
meat, poultry, eggs
12-36 hrs
clostridium botulinum
canned foods, smoked fish
12 hours
vibrio parahemolyticus
raw fish, shellfish
24-48 hours
contaminated by carrier, not foodborne
Which Food borne illeness has the highest percentage?
Bacteria (40 agents)
-salmonella, staph aureus
What percentage is bacteria?
68.7 %
Most bacteria require a
potentiall yhazardous food
a potentially hazardous food is one that is high in
protein and moist
milk or egg products, eggs, meat, poultry and fine shellfish crustaceans, raw seed sprouts heat treated veggies and veggie products
are potentially hazardous foods
There is a systematic way to investigate
epidemic curves give us clues to the
mode of transmission
attack rates help determine the
source of an outbreak
food-borne outbreaks are a common problem and areoften the result of
improper food handling and storage
Epidemiological triad concepts
All 3 epidemiological triad concepts are dependent on the condition of the host:
Measures the ability to invade a host
Formula for infectivity
number of infected / number of susceptible x 100
measures the ability to cause disease
formula for pathogenicity
number with clinical disease/ number of infected x 100
measures the severity of disease
formula for virulence
number of deaths/ number of people with the disease x100
Ability to become infected with an organism when exposed to it.