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Microbiology > 5.59 > Flashcards

5.59 Flashcards

1
Q

Epidemiology

A

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

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2
Q

• sporadic disease (example: histoplasmosis, gas gangrene)

A

– occurs occasionally and at irregular intervals

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3
Q

• endemic disease (example: gonorrhea, Dengue fever)

A

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

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4
Q

• holoendemic diseases (example: malaria)

A

– occurs at a high, constant level throughout a population

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5
Q

• epidemic (example: influenza, meningococcal infections)

2

A

– sudden increase in frequency above expected number

– index case – first case in an epidemic

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6
Q

• outbreak

A

– sudden, unexpected occurrence of disease

– usually focal or in a limited segment of population

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7
Q

• pandemic

A

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

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8
Q

Morbidity rate

A
  • an incidence rate
  • number of new cases in a specific time period per unit of population
equation
# new cases during a specific time over
# individuals in population
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9
Q

Prevalence rate

2

A
  • total number of individuals infected at any one time per unit of population
  • depends both on incidence rate and duration of illness
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10
Q

Mortality rate

A

• number of deaths from a disease per number of cases of the disease

equation
# deaths due to given disease over
size of total population with disease

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11
Q

R0 or R(0), “R-naught” =

A

number of secondary cases one case would

produce in a completely susceptible population

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12
Q

R(0) calculated as a function of 3 primary parameters

A

• 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

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13
Q

Recognition of an Infectious
Disease in a Population
(2)

A

• involves use of surveillance methods
• cases of a disease recognized by its characteristic
disease syndrome

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14
Q

cases of a disease recognized by its characteristic
disease syndrome
(3)

A

– set of signs and symptoms characteristic of a disease
– signs
– symptoms

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15
Q

– signs

A

• objective changes in body that can be directly observed

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16
Q

– symptoms

A

• subjective changes experienced by patient

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17
Q

• incubation period

A

– period after pathogen entry but before

signs and symptoms appear

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18
Q

• prodromal stage

2

A

– onset of signs and symptoms

– not clear enough for diagnosis

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19
Q

• period of illness

A

– disease is most severe and has

characteristic signs and symptoms

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20
Q

• convalescence

A

– signs and symptoms begin to disappear

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21
Q

skipped
Correlation with a Single Causative Agent
(2)

A

• after recognition of infectious disease in a population, outbreak
correlated with specific pathogen [e.g. HIV/AIDS (early 1980s), SARS
CoV (2003), SARS-CoV-2 (2019-2020)]
• clinical microbiologists help in isolation and identification of pathogen

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22
Q

Recognition of an Epidemic

• 2 types of epidemics

A

common source epidemic

propagated epidemic

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23
Q

threshold density =

A

the minimum number of individuals necessary to continue propagating the disease

24
Q

Herd immunity

A

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

25
Q

Herd immunity

• level can be altered by

A

introduction of new susceptible

individuals into population

26
Q

Herd immunity

• level can be altered by changes in

A

pathogen

27
Q

– antigenic shift –

A

major change in antigenic character of pathogen

28
Q

– antigenic drift –

A

smaller antigenic changes

29
Q
  1. What Pathogen Caused the Disease?

3

A 
• Kochs postulates (or
modifications) are used if
possible
• clinical microbiology lab
• communicable disease
30
Q

clinical microbiology lab

A

– plays important role in
isolation and identification of
pathogen

31
Q

communicable disease

A

– can be transmitted from one

host to another

32
Q

source

A

– location from which pathogen

is transmitted to host

33
Q

• period of infectivity

A

– time during which source is
infectious or is disseminating
the organism

34
Q

• reservoir (2)

A 
– site or natural environmental
location in which pathogen is
normally found
– sometimes functions as
source of pathogen
35
Q

Human sources/reservoirs
• carrier
(3)

A

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

36
Q

active carrier

A

– has overt clinical case of disease

37
Q

• convalescent carrier

A

– has recovered from disease but continues to harbor large

numbers of pathogen

38
Q

• healthy carrier

A

– harbors pathogen but is not ill

39
Q

• incubatory carrier

A

– harbors pathogen but is not yet ill

40
Q

Animal reservoirs

3

A
  • numerous diseases are zoonoses
  • transmission to human can be direct or indirect
  • vectors– organisms that spread disease from one host to another
41
Q
  1. Airborne Transmission

3

A
  • pathogen suspended in air and travels ³ 1 meter
  • droplet nuclei
  • dust particles also important route of airborne transmission
42
Q

• droplet nuclei

4

A

– 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

43
Q

Contact Transmission

3

A
  • coming together or touching of source/reservoir and host
  • direct contact (person-to-person)
  • droplet spread
44
Q

• direct contact (person-to-person)

2

A

physical interaction between source/reservoir and host

– e.g., kissing, touching, and sexual contact

45
Q

droplet spread

A

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

46
Q

Vehicle Transmission

• Vehicles =

A

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

47
Q

. Vector-Borne Transmission
• external (mechanical) transmission
(2)

A

– passive carriage of pathogen on body of vector

– no growth of pathogen during transmission

48
Q

. Vector-Borne Transmission
• internal transmission
(3)

A

– 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)

49
Q

Why Was the Host Susceptible to the Pathogen?

• two main factors

A

– defense mechanisms of host

– pathogenicity of pathogen

50
Q
  1. How Did the Pathogen Leave the Host? (2)
A
  • active escape

* passive escape

51
Q

active escape

A

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

52
Q

passive escape

A

– excretion in feces, urine, droplets, saliva, or

desquamated cells [microbes]

53
Q

Control of Epidemics (3)

A
  1. Reduce or eliminate source or reservoir
  2. Break connection between source and susceptible individuals\
  3. Reduce number of susceptible individuals
54
Q
  1. Reduce or eliminate source or reservoir

4

A

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

55
Q
  1. Break connection between source and susceptible individuals
    (4)
A

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

56
Q
  1. Reduce number of susceptible individuals

2

A

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

Microbiology (42 decks)

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