Epidemiology Flashcards
What are the three critical questions when investigating occurrence of disease?
Who was attacked by the disease(sex, age. race)?
When did the disease occur (winter summer, year)?
Where did the cases arise (isolated region or across country)?
What is attack rate?
% of people at risk in population
What is the attack rate used for?
to predict number of cases expected during an epidemic and to analyze. disease outbreak
Time is not specified because exposure is common and illness is acute
What is the difference between primary and secondary cases?
Primary cases acquire disease from the pathogen and secondary cases acquire the disease from primary cases. Depends on source of exposure.
How do you calculate the attack rate?
no. of people at risk in whom a certain illness develops/ total number of people at risk
E.g no. of people who ate a certain food and became ill/ total no. of people who ate that food
3 important questions to answer when investigating an outbreak
When did the exposure take place?
When were symptoms apparent?
What is the incubation period?
Why disease does not develop immediately at time of infection?
Needs time to replicate and depends on site of body in which it replicates
Dose of infectious agent received at time of infection can influence incubation period
Large dose= short incubation
Define incubation period
Interval from receipt of infection to onset of clinical illness.
Time it takes for a disease to develop after exposure to a pathogen
depends on disease
disease can be transmitted during incubation
What is herd immunity?
principle that if a large % of population is immune to a particular disease, the entire population is protected as well as those who are immune
Conditions to meet herd immunity
disease agent must be restricted to a single host species within which transmission occurs
if we have a reservoir in which the organism can exist outside the human host, herd immunity will not operate because we have another means of transmission
infections must induce solid immunity. If immunity is only partial we will not build up a large proportion of immune people in the community
Types of exposure
single exposure- exposed once
Common-vehicle exposure- group of people have eaten contaminated food and become ill
Multiple exposure- exposed more than once
Define endemic, epidemic and pandemic
Endemic- habitual occurrence of a disease within a given geographical area
Epidemic- occurrence in a a community or region of a group of illnesses of similar nature
Pandemic-worldwide epidemic
Types of non-clinical diseases
Preclinical -not yet clinically apparent but is destined to become a clinical disease
Subclinical-not yet clinically apparent and is not destined to become clinically apparent. This type of disease is often diagnosed by serologic (antibody) response or culture.
Persistent (chronic)- person fails to hake off infection and it persists for years at times for life
Latent- infection with no active multiplication of the agent
Iceberg concept of infectious diseases
Only a small portion of infections result in clinical disease
Modes of disease transmission
Direct- droplet (cough, sneeze), direct physical contact( sexual), transplacental ( mother to child)
Indirect- food, air water borne, indirect physical contact( touching surfaces), vector e.g insect
Portals of entry
genital respiratory (upper and lower airways) urinary gastrointestinal (mouth) damaged skin(cuts and burns)
Factors that may be associated with increased risk of disease
Host charcteristics- age,sex,race,religion.customs,occupation
Type of agents- virus, bacteria, alcohol, smoke, radiation
Environmental factors- temperature, humidity, altitude
Epidemiologic triad of disease
Host
/ i \
Vector \
/ / \
Agent ——- Environment
Two approaches of disease prevention
Population-based
High risk approach
Can be combined
Population based approach
applied to entire population
may use mass media or other health education approaches
must be inexpensive and noninvasive
can be considered public health approach
High risk approach
screening for certain disease
may be restricted to children from high risk families
may be more expensive, invasive or inconvenient
must be able to identify individuals with disease
require clinical action to identify high risk groups
History of epidemiology
John snow -cholera
Edward Jenner- small pox
Ignaz Semelweis-childbed fever
The epidemiological approach
1- identify cause and distribution of disease
determine if there is an association between exposure factor or characteristic and development of disease
if pattern and association exists determine if there is a causal relationship
-if there is a causal relationship: does factor increase risk of disease development
lead to development of disease
cause disease
Population data for clinical practice comes from:
surgeries
autopsies
experience with large group of patients who have had the disease
clinical trials
