epidemilogy

Question 1

Epidemiology

Answer 1

• science that evaluates occurrence, determinants, distribution, and control of health and disease in a defined human population

Question 2

sporadic disease

examples?

Answer 2

example: histoplasmosis, gas gangrene

– occurs occasionally and at irregular intervals

Question 3

endemic disease

examples?

Answer 3

example: gonorrhea, Dengue fever

– maintains a relatively steady low-level frequency at a moderately regular interval

Question 4

holoendemic diseases

Answer 4

(example: malaria)

– occurs at a high, constant level throughout a population

Question 5

epidemic
examples?
index case?

Answer 5

example: influenza, meningococcal infections
– sudden increase in frequency above expected number
– index case – first case in an epidemic

Question 6

outbreak

Answer 6

– sudden, unexpected occurrence of disease

– usually focal or in a limited segment of population

Question 7

pandemic

Answer 7

– increase in disease occurrence within large population over wide region
(usually worldwide)

Question 8

Morbidity rate

Answer 8

• 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

Question 9

Prevalence rate

depends on?

Answer 9

• total number of individuals infected at any one time per unit of population
• depends both on incidence rate and duration of illness

Question 10

Mortality rate

Answer 10

• number of deaths from a disease per number of cases of the disease
# deaths due to given disease/ size of total population with disease

Question 11

R0 or R(0), “R-naught”

Answer 11

number of secondary cases one case would produce in a completely susceptible population, measure of contagious

Question 12

R(0) calculated as a function of?

Answer 12

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

Question 13

Recognition of an Infectious Disease in a Population

use of?

Answer 13

• 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

Question 14

Course of infectious disease

Answer 14

incubation, prodromal, period of illness, convalesence

Question 15

incubation period

Answer 15

– period after pathogen entry but before

signs and symptoms appear

Question 16

prodromal stage

Answer 16

– onset of signs and symptoms

– not clear enough for diagnosis

Question 17

period of illness

Answer 17

– disease is most severe and has

characteristic signs and symptoms

Question 18

convalescence

Answer 18

– signs and symptoms begin to disappear

Question 19

Correlation with a Single Causative Agent

Answer 19

after recognition of infectious disease in a population, outbreak correlated with specific pathogen
clinical microbiologists help in isolation and identification of pathogen

Question 20

2 types of epidemics

Answer 20

common source epidemics- rapid rise and fall

propogated epidemics- prolonged

Question 21

propagated epidemics and threshold density

Answer 21

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

Question 22

Herd immunity

Answer 22

resistance of a population to infection and to spread of an infectious organism because of the immunity of a large percentage of the population

Question 23

factors decreasing the level of herd immunity

Answer 23

• 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

Question 24

The Infectious Disease Cycle questions to ask

Answer 24

1. What Pathogen Caused the Disease?
2. What was the Source and/or Reservoir of the Pathogen?
3. How Was the Pathogen Transmitted?
4. Why Was the Host Susceptible to the Pathogen?
5. How Did the Pathogen Leave the Host?

Question 25

1. What Pathogen Caused the Disease?

Answer 25

• Kochs postulates (or modifications) are used if possible
• clinical microbiology lab – plays important role in isolation and identification of pathogen
• communicable disease – can be transmitted from one host to another

Question 26

2. What was the Source and/or Reservoir of the Pathogen?

source? reservoir? Period of infectivity?

Answer 26

• source – location from which pathogen is transmitted to host
• period of infectivity – time during which source is infectious or is disseminating the organism

• reservoir – site or natural environmental location in which pathogen is normally found
– sometimes functions assource of pathogen

Question 27

Human sources/reservoirs are called?

potential time frames?

Answer 27

• carrier
– infected host
– can be casual (acute or transient) carrier – short time
– can be chronic carrier – long time

Question 28

types of carriers

Answer 28

• active carrier – has overt clinical case of disease
• convalescent carrier – has recovered from disease but continues to harbor large numbers of pathogen
• healthy carrier – harbors pathogen but is not ill
• incubatory carrier – harbors pathogen but is not yet ill

Question 29

Animal reservoirs

vectors?

Answer 29

• numerous diseases are zoonoses
• transmission to human can be direct or indirect
• vectors– organisms that spread disease from one host to another

Question 30

modes of transmission

Answer 30

1. Airborne Transmission
2. Contact Transmission
3. Vehicle Transmission
4. Vector-Borne Transmission

Question 31

Airborne Transmission

Answer 31

pathogen suspended in air and travels ³ 1 meter

• droplet nuclei
– small particles (1-4 micrometers in diameter)
– can remain airborne for long time (hours to days)
– can travel long distances
– usually propelled from respiratory tract of source organisms by sneezing, coughing, or vocalization

• dust particles also important route of airborne transmission

Question 32

Contact Transmission

Answer 32

• coming together or touching of source/reservoir and host

• direct contact (person-to-person)
– physical interaction between source/reservoir and host
– e.g., kissing, touching, and sexual contact

• droplet spread
– large particles (>5 micrometers) that travel < 1 meter

Question 33

Vehicle Transmission

Answer 33

• Vehicles = inanimate materials or objects involved in pathogen transmission
– water and food (spread pathogen to multiple hosts)
– fomites = inanimate objects: surgical instruments, bedding and eating utensils

Question 34

Vector-Borne Transmission, types?

Answer 34

• external (mechanical) transmission
– passive carriage of pathogen on body of vector
– no growth of pathogen during transmission

• internal transmission
– carried within vector
– harborage transmission – pathogen does not undergo changes within vector (bubonic plaque: Yersinia pestis in flea)
– biologic transmission – pathogen undergoes changes within vector
(malaria: Plasmodium spp. in Anopheles spp. mosquito)

Question 35

Why Was the Host Susceptible to the Pathogen?

Answer 35

– defense mechanisms of host

– pathogenicity of pathogen

Question 36

escape routes from the host

Answer 36

• active escape
– movement of pathogen to portal of exit [helminths (worms) that migrate through the body of the host]

• passive escape
– excretion in feces, urine, droplets, saliva, or desquamated cells [microbes]

Question 37

Control of Epidemics

Answer 37

Reduce or eliminate source or reservoir
Break connection between source and susceptible individuals
Reduce number of susceptible individuals

Question 38

How to Reduce or eliminate source or reservoir

Answer 38

– quarantine and isolation of cases and carriers
– destruction of animal reservoir
– treatment of sewage
– therapy that reduces or eliminates infectivity of cases

Question 39

How to Break connection between source and susceptible individuals

Answer 39

– chlorination of water supplies
– pasteurization of milk
– supervision & inspection of food & food handlers
– destruction of insect vectors with pesticides

Question 40

How to Reduce number of susceptible individuals

Answer 40

– passive immunity following exposure
– active immunity for protection
both augment herd immunity