Basic concepts in Epidemiology Flashcards
Occurrence of a Disease
• Incidence and prevelance
Incidence: definition
Incidence rate formula
Incidence: Describe the rate of development of a disease
in a group over a period of time.
Nbr of persons dev. a disease x unit time = Incidence rate
Total number at risk
Incidence: examples
The incidence of chickenpox in first-grade
children was 10 percent a day at the height
of the epidemic
Chick poxs
- Varicellovirus
Double stranded dna virus
- The incidence of myocardial infarction is
about 1 percent per year in men aged 55
to 59 in our community
I Prevalence: definition
Prevlance formula
Number of persons with a disease
is the most frequently used measure in epidemiology.
For a count to be descriptive of a group, it has to be
considered as proportion of a group.
Prevalence: Describe a group at a certain point in time.
Number of persons with a disease = Prevalence rate
Total number in group
Total # of dieases over number in group will give u rate of prevelance
Prevalence: examples
Prevalence of diarrhea in the children’s camp on July 13 was 33 percent
- Prevalence of significant hyperbilirubinemia in full-term infants on the third post-partum
day is 20 percent - Prevalence of electrocardiographic
abnormalities at our screening examination
was 5 percent
Morbidity rate: definition
Morbidity: incidence of illness (disease) in a population.
It includes both fatal and nonfatal diseases.
Morbidity rate could refer to either prevalence or
incidence.
Morbidity rates: examples
Morbidity rate of genital Chlamydia in Canada in 2000
was 32%.
Morbidity rate of giardiasis in Canada in 2000 was 3.4%.
These are the number of new cases for the year 2000.
Mortality rate: definition
formula
Mortality: incidence of death in a population.
Nbr of persons dead x unit time = Mortality rate
Total number in group
Mortality rate: examples
The mortality rate varied from 25% to 33% of
Europe’s population during plague epidemics
in the Middle Ages.
- The mortality rate of HIV/AIDS patients in the
USA decreased from 15.6 deaths per 100,000
people in 1995 to 11.6 deaths per 100,000 people
in 1996.
Case Fatality Ratio
Usually in an epidemiological study (often outbreak).
• The number of confirmed cases that died of the diseases.
• It is an estimate on a small sample of the mortality rate of a disease
(estimate because not all cases in outbreak has been reported)
It is usuually for people that have been confirmed based on pcr
Listeria monocytogenes
- Food path 150 cases in canad a - CFR- 15-30% - High case F R = leads people to start implementing containment early
Occurrence of a Disease the types
Sporadic disease: disease that occurs only occasionally
• Endemic disease: disease constantly present in a population
• Epidemic disease: disease acquired by many people in a given area in
a short time
• Pandemic disease: worldwide epidemic
The notifiable are usually endemic
May change if u have a way of vaccinatingg or treating ie measels
Epidem - usully unstable pop
When that goes global = pandemic
Example of a pandemic
Hiv exapmle of pandemic
1979 first cases
Luc montagnier - france
Robert gallo - usa (NIH new your
Isolate dthe virus
92-93 change of case definition gence the spike as the number befroe were probs underreporting
Case Definition of TB
A tuberculosis (TB) case is a patient that has been diagnosed as such
by a clinician, regardless if the diagnosis has been confirmed
bacteriologically or not.
• The elements necessary for defining a TB case are: the TB treatment
history, the bacteriological status, the anatomical site of the disease
and the patient’s HIV status.
• Note: any person receiving treatment for TB should be recorded as a
TB case.
• (derives from WHO guidelines)
Acute disease
symptoms develop rapidly but the disease lasts only a
short time
Chronic disease
: symptoms develop slowly
Cronic- hep c - will have acute phase followe dby cronic infectionn
Subacute disease:
: intermediate between acute
and chronic
Latent disease
causative agent is inactive for a time but then
activates and produces symptoms
tuverculosis, hep, conjuctivitis caused by herpes
Herpes simplex- the dna of virus will incorperated into dna of host cfell - 1% of people after 50 years will give an infection
Vairacella (chicken pox) - gives shingles in latent state , uaully is a nerve infectin
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
exp is strep pyogenes
Focal infection
systemic infection that began as a local infection
Sepsis
: toxic inflammatory condition arising from the spread of
microbes, especially bacteria or their toxins, from a focus of infection
Bacteremia
bacteria in the blood
- may start by a simple brushing of teeth too hard
- Does not involve growth of bact
Septicemia
also known as blood poisoning; growth of bacteria in the
blood
Toxemia
toxins in the blood
diptheria - a single unit, has an a part and b part, b is active part
Viremia
viruses in the blood
measles for unvax childrens
Primary infection:
acute infection that causes the initial illness
Secondary infection
opportunistic infection after a primary
(predisposing) infection
You may have cold or flu and u may have probkem in lungs and may develop bect which is secondary infec
Subclinical disease
no noticeable signs or symptoms (inapparent
infection)
Predisposing Factors
Gender • Inherited traits, such as the sickle cell gene • Climate and weather • Fatigue • Age • Lifestyle • Nutrition • Chemotherapy
Inherited- nRAMP
Inherited- nRAMP - 1 protien (gene)- associated with succeptability or resisiance
- The polymorphasm of this has been studied - connection to indigenous which makes them more succept to tuberculuosus
Another exampke is ccr5 gene - HIV- plymorphus - variable in dif contries
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
goes back to norma
Reservoirs of Infection
Continual sources of infection Human reservoirs • Carriers may have inapparent infections or latent diseases Animal reservoirs • Zoonoses are diseases transmitted from animals to humans Nonliving reservoirs • Soil and water • Food
Direct contact transmission
requires close association between the
infected and a susceptible host
Indirect contact transmission
spreads to a host by a nonliving object
called a fomite
Fomite- important for hospital infections
Droplet transmission
transmission via airborne droplets less than 1
meter