Chapter 59: Principles of Epidemiology Flashcards
what is epidemiology
science that evaluates occurrence, determinants, distribution and control of health and disease in a defined human population
what is sporadic disease and give example
- occurs occasionally and at irregular intervals
- histoplasmosis
- gas gangrene
what is endemic disease and give examples
- maintains a relatively steady low level frequency at a moderately regular interval
- gonorrhea
- dengue fever
what is holoendemic diseases and what is an example
- occurs at a high, constant level throughout a population
- malaria
what is epidemic and give exmaple
- sudden increase in frequency above expected number
- influenza and meningococcal infection
what is the first case in an epidemic called
index case
what is an outbreak
sudden unexpected occurrence of disease
- usually focal or in a limited segment of population
what is a pandemic
increase in disease occurrence within large population over wide region
what is morbidity rate
- an incidence rate
- number of new cases in a specific time period per unit of population
what is prevalance rate
- total number of individuals infected at any one time per unit of population
- depends both on incidence rate and duration of illness
what is mortality rate
number of deaths from a disease per number of cases of the disease
what is R0 or R naught
number of secondary cases one case would produce in a completely susceptible population
R(0) calculated as a function of 3 primary parameters
- duration of contagiousness after a person becomes infection
- likelihood of infection per contact between a susceptible person and an infectious person or vector
- contact rate
what does infectious disease epidemioogy try to determine
- causative agent
- source and/or resevoir of disease agent
- mechanism of transmission
- host and environmental factors that facilitate development of disease within a defined population
- best control measures
what are signs
objective changes in body that can be directly observed
what are symptoms
subjective changes experienced by patient
what is the course of infectious disease
-incubation period
- prodromal stage
- period of illness
- convalescence
what is the incubation period
period after pathogen entry but before signs and symptoms appear
what is prodromal stage
onset of signs and symptoms
- not clear enough for diagnosis
what is period of illness
disease is most severe and has characterisitc signs and symptoms
what is convalescence
signs and symptoms begin to disappear
what are the 2 types of epidemics
common source epidemics and propagated epidemic
what is threshold density
minimum number of individuals necessary to continue propagating the disease
what is 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
what is antigenic shift
major change in antigenic character of pathogen
what is antigenic drift
smaller antigenic changes
what is a source
location from which the pathogen is transmitted to the host
what is period of infectivity
time during which source is infectious or disseminating the organism
what is a reservoir
site or natural environmental location in which pathogen in normally found
- can function as source of pathogen
what is an active carrier
has overt clinical case of disease
what is convalescent carrier
has recovered from disease but continues to harbor large numbers of pathogen
what is a healthy carrier
harbors pathogen but is not ill
what is an incubatory carrier
harbors pathogen but it not YET ill
describe animal reservoirs
- numerous diseases are zoonosed
- ## transmission to human can be direct or indirect
what are vectors
organisms that spread disease from one host to another
what are the types of airborne transmission
- pathogen suspended in air and travels more than 1 meter
- droplet nuclei
- dust particles
describe droplet nuclei
small particles
- can remain airborne for llong time
- can travel long distances
- usually propelled from respiratory tract of source organisms by sneezing, coughing or vocalization
what is contact transmission
- coming together or touching of source/ reservoir and host
- direct contact
- droplet spread
what are vehicles of transmission
inanimate materials or objects involved in pathogen transmission
what is external vector borne transmission
passive carriage of pathogen on body of vector
- no growth of pathogen during transmission
what is internal transmission of vectors
- carried within vector
- harborage transmission - pathogen does not undergo changes within vectro
- biologic trnasmission- pathogen undergoes changes within vector
why is a host susceptible to a pathogen
- defense mechanisms of the host
- pathogenicity of pathogen
how does a pathogen leave the host
- active escape: movement of pathogen to portal of exit
- passive escape: excretion in feces, urine, droplets, saliva or desquaminated cells
how are epidemics controlled
- reduce or eliminate source of reservoir
- break connection between source and susceptible individuals
- reduce number of susceptible individuals
how are reservoirs reduced or eliminated
- quarantine and isolation of cases and carriers
- destruction of animal reservoir
- treatment of sewage
- therapy that reduced or eliminates infectivity of cases
how is connection between source and susceptible individuals broken
- chlorination of water supplies
- pasteruization of milk
- supervision and insepction of food and food handlers
- destruction of insect vectors with pesticides
how is the number of susceptible individuals reduced
- passive immunity following exposure
- active immunity for protection
- herd immunity
