epidemilogy Flashcards
(40 cards)
Epidemiology
• science that evaluates occurrence, determinants, distribution, and control of health and disease in a defined human population
sporadic disease
examples?
example: histoplasmosis, gas gangrene
– occurs occasionally and at irregular intervals
endemic disease
examples?
example: gonorrhea, Dengue fever
– maintains a relatively steady low-level frequency at a moderately regular interval
holoendemic diseases
(example: malaria)
– occurs at a high, constant level throughout a population
epidemic
examples?
index case?
example: influenza, meningococcal infections
– sudden increase in frequency above expected number
– index case – first case in an epidemic
outbreak
– sudden, unexpected occurrence of disease
– usually focal or in a limited segment of population
pandemic
– increase in disease occurrence within large population over wide region
(usually worldwide)
Morbidity rate
- an incidence rate
- number of new cases in a specific time period per unit of population
new cases during a specific time/ # individuals in population
Prevalence rate
depends on?
- total number of individuals infected at any one time per unit of population
- depends both on incidence rate and duration of illness
Mortality rate
• number of deaths from a disease per number of cases of the disease # deaths due to given disease/ size of total population with disease
R0 or R(0), “R-naught”
number of secondary cases one case would produce in a completely susceptible population, measure of contagious
R(0) calculated as a function of?
3 primary parameters
• duration of contagiousness after a person becomes infected
• likelihood of infection per contact between a susceptible person and an infectious person or vector
• contact rate
Recognition of an Infectious Disease in a Population
use of?
• involves use of surveillance methods
• cases of a disease recognized by its characteristic disease syndrome
– set of signs and symptoms characteristic of a disease
– signs
• objective changes in body that can be directly observed
– symptoms
• subjective changes experienced by patient
Course of infectious disease
incubation, prodromal, period of illness, convalesence
incubation period
– period after pathogen entry but before
signs and symptoms appear
prodromal stage
– onset of signs and symptoms
– not clear enough for diagnosis
period of illness
– disease is most severe and has
characteristic signs and symptoms
convalescence
– signs and symptoms begin to disappear
Correlation with a Single Causative Agent
after recognition of infectious disease in a population, outbreak correlated with specific pathogen
clinical microbiologists help in isolation and identification of pathogen
2 types of epidemics
common source epidemics- rapid rise and fall
propogated epidemics- prolonged
propagated epidemics and threshold density
as the number of cases rises and more people recover there is a lower number os susceptible individuals= less cases
once this number drops below the threshold density the epidemic will slow down
threshold = minimum number of individuals necessary to continue propagating the disease
Herd immunity
resistance of a population to infection and to spread of an infectious organism because of the immunity of a large percentage of the population
factors decreasing the level of herd immunity
• level can be altered by introduction of new susceptible individuals into population
• level can be altered by changes in pathogen
– antigenic shift – major change in antigenic character of pathogen
– antigenic drift – smaller antigenic changes
The Infectious Disease Cycle questions to ask
- What Pathogen Caused the Disease?
- What was the Source and/or Reservoir of the Pathogen?
- How Was the Pathogen Transmitted?
- Why Was the Host Susceptible to the Pathogen?
- How Did the Pathogen Leave the Host?
