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Microbiology > Communicable diseases > Flashcards

Communicable diseases Flashcards

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1
Q

Epidemiologic triad

A
  1. Host (demographic, socioeconomic, biological)
  2. Agent (chemical,biological,physical,nutrient,mechanical,social)
  3. Environment (physical, biological, social)
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2
Q

Definition of communicable diseases

A

An illness caused due to specific infectious (biological) agent or its toxic products capable of being directly or indirectly transmitted from man to man, animal to man animal to animal or from the environment to man

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3
Q

Roles of epidemiology

A
  1. Monitor public health (mortality, morbidity rates)
  2. Respond to outbreaks, pandemics, epidemics (determine cause of outbreak, put in control measures)
  3. Investigate emerging and reemerging diseases (determine risk factors, recommend control measures)
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4
Q

Why is it important to study epidemiology of communicable diseases?

A

Changes of pattern of infectious disease
Discovery of new infections
Possibility that some chronic diseases have an infective origin

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5
Q

Definition of infection

A

Entry and development/multiplication of an infectious agent in the body of a man/animals
An infection does not always cause illness (asymptomatic)

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6
Q

Levels of infection (gradients)

A
  1. Colonisation- prescence of infectious agent doesn’t mean infection straight away, e.g S.aureus in skin and normal nasopharynx
  2. Subclinical- infection but no signs/symptoms e.g polio
  3. Latent infection- prescence of infectious agent but no symptoms e.g herpes simplex virus
  4. Manifest/clinical infection- infectious and showing symptoms
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7
Q

Meaning of contamination

A

Presence of an infectious agent on a body surface/ clothing/bedding/toys/surgical instruments/water/food

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8
Q

Meaning of infestation

A

Lodgement, development and reproduction of arthropods on the surface of a body/clothing
e.g lice/mites
Term can be used to describe invasion of gut by parasitic worms e.g ascariasis

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9
Q

Meaning of contagious disease

A

Disease transmitted trhough contact

e.g leprosy, scabies, STIs

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10
Q

Meaning of reservoir host

A

Person/animal/arthropod/soil/plant/substance in which an infectious agent normally lives and multiplies
natural habitat of infectious agent
depends on it for survival
reproduces so it can be transmitted to a susceptible host

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11
Q

Meaning of incidence

A

Number of new cases in a given time period expressed as percent of infected per year (cumulative incidence)
or incidence density= number of cases per person time of observation

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12
Q

Meaning of prevalence

A

Number of cases at a given time expressed a as percent at a given time
Incidence x duration

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13
Q

What disease has a short duration?

A

Measles

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14
Q

What disease has a long duration?

A

Chronic hepatitis B

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15
Q

Meaning of epidemic

A

Unusual occurrence of disease in a community
specific health related behaviour/ health related events
in excess of expected occurrence

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16
Q

Meaning of endemic

A

Constant presence of disease/infectious agent within a geographic area/population group
It is the usual/ expected frequency of disease within a population

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17
Q

Meaning of pandemic

A

An epidemic affecting large proportion of population occuring over a wide geographic area e.g section of nation/continent/world e.g influenza pandemics

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18
Q

Meaning of exotic diseases

A

imported into a country where they do not normally occur in e.g rabies in UK

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19
Q

Meaning of sporadic

A

cases are ‘scattered about’
Irregular, from time to time
Cases are few and separated widely in time
show no/little connection with each other/ recognizable source of infection e.g polio/meningococcal meningitis

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20
Q

What can a sporadic disease lead to?

A

Starting point of an epidemic

If conditions are favourable for its spread

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21
Q

Meaning of epizootic

A

Epizoic= outbreak (epidemic) of a disease within an animal population e.g rift valley fever

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22
Q

Meaning of Enzootic

A

Endemic occurring in animals e.g bovine TB

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23
Q

What is a nosocomial infection?

A

Hospital acquired infection
Infection originating in a paitent while in hospital
Has to be a new disorder unrelated to primary condition of patient
e.g surgical wounds, hepatitis B, UTI

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24
Q

What are the 2 types of epidemic?

A
  1. Common source

2. Propagated

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25
Q

What is a common source epidemic?

A

Rapid rise and fall of incidence

Arises from a single source e.g food poisoning/legionnaire’s disease

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26
Q

What is a propagated epidemic?

A

Slow rise and fall of incidence
Disease may be transmitted from each contaminated individual
e.g strep throat

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27
Q

What is an opportunistic infection?

A

Infection by organisms that take the opportunity provided by a defect in the host (e.g weakened immune system) to infect the host and cause disease
This disease wouldn’t occur in individuals with a healthy immune system

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28
Q

Example of opportunistic infections

A

Common in AIDS
M.tuberculosis
Herpes simplez virus

29
Q

Meaning of eradication

A

Termination of all transmission of infection by extermination of infectious agent
Through surveillance and containment

30
Q

Meaning of elimination

A

Eradication of disease in a large geographic area

31
Q

What diseases are currently easily eliminated?

A

Polio,measles, diphtheria

32
Q

What is the attack rate?

A

Proportion of non-immune exposed individuals who become clinically ill

33
Q

What is a primary and second case?

A

Primary case= person who comes into and jnfects population
secondary case= those that subsequently contract the infection
further spread= waves/generations

34
Q

What is the reproductive rate/number (R)?

A

Average number of new infections caused by 1 infected individual

35
Q

Meaning of R0?

A

Basic reproductive rate in an entirely susceptible population

36
Q

What is the effective reproductive rate in a population where <100% are susceptible?

A

R= proportion susceptible x R0

37
Q

What does it mean if R0>1?

A

Infection spreads (epidemic)

38
Q

What does it mean if R0=1?

A

Infection remains constant (endemic)

39
Q

What does it mean if R0<1?

A

Infection dies out

40
Q

Determinants of R0 formula

A

R0= B (beta) x c x D

B= probability of transmission per contact between an infected and susceptible individual 
c= contact rate 
D= duration of infectivity
41
Q

What is the mathematical SIR model

A

Susceptible-infectious-recovered model
epidemiological model that computes the theoretical number of people infected with a contagious illness in a closed population over time

42
Q

Assumptions of SIR model

A

Latent period= 0
population is fixed- no births/deaths
Infectious period= duration period
After recovery, individuals are immune

43
Q

Parameters needed to use model

A

effective contact rate, natural mortality rate, recovery rate, and disease-induced death rate

44
Q

What are the 3 different types of reservoirs?

A

Human- look at diagram
Animal
Non-living

45
Q

What is ‘case’?

A

A person in the population/study group identified as having the particular disease/health condition/disorder/condition under investigation

46
Q

What is a ‘carrier’?

A

Infected person/animal that is infected with a specific infectious agent
absence of visible clinical disease
Acts as a potential source of infection to others

47
Q

How does someone become a carrier?

A

Inadequate treatment/immune response

disease is not completely eliminated

48
Q

What are the 3 elements that form a carrier state?

A
  1. Presence of disease agent in body
  2. Absence of recognisable symptoms and signs of disease
  3. Shedding of disease agent in discharge/excretion
49
Q

What can act as a reservoir of infection?

A
  1. Soil- can harbor agents that cause anthrax, tetanus

2. Inanimate matter

50
Q

DIfferent modes of transmission

A
  1. Direct transmission- direct contact, droplet infection, contact with soil, inoculation into skin/mucosa, vertical
  2. Indirect- fomite, vector(look at diagram), air borne, vehicle borne
51
Q

Meaning of a susceptible host

A

An infectious agent seeks a susceptible host to aim for successful parasitism

52
Q

What 4 stages are required for successful parasitism?

A
  1. Portal of entry into host
  2. Site of election inside body
  3. Portal of exit out of host
  4. Survival in external environment
53
Q

Meaning of virulence

A

Degree of pathogenicity

54
Q

How is virulence numerically expressed?

A

ratio of number of cases: total number infected

determined by immunoassay (measures concentration of antibody in body)

55
Q

Meaning of case fatality rate?

A

Proportion of infected individuals who die from infection
no. of deaths/no of cases
depends on severity of infection (virulence)
heavily influenced about no of mild cases not diagnosed

56
Q

Meaning of serial interval (generation time)

A

Gap in time between the onset of the primary and secondary cases
Interval between recipient of infection and maximal infectivity of host

57
Q

What is the infectious period?

A

length of time a person can transmit disease

58
Q

What is the incubation period?

A

Time interval between invasion by infectious agent and appearance of first sign/symptom of disease

59
Q

What is the latent period?

A

Period between being infected to becoming infectious

60
Q

What is a transmission probability ratio (TPR)?

A

Measure of risk of transmission from an infected to a susceptible individual during contact
TPR of differing types of contacts, infectious agents, infection routes and strains can be calculated

61
Q

4 types of TPRs

A

p00
p01
p10
p11

62
Q

p00

A

p00= tp from unvaccinated infective to unvaccinated susceptible

63
Q

p01

A

p01= tp from vaccinated infective to unvaccinated susceptible

64
Q

p10

A

p10= tp from unvaccinated infected to vaccinated susceptible

65
Q

p11

A

p11= tp from vaccinated infected to vaccinated susceptible

66
Q

How are diseases investigated in the clinic?

A
  1. Collate symptoms
  2. Foods eaten
  3. Location foods eaten in
  4. Secondary attacks
67
Q

How are diseases investigated in the lab?

A
  1. Preliminary culture
  2. Attack rate analysis
  3. Antibiotic analysis
  4. definitive ID
  5. Sample culture
  6. Reference culture
  7. Deposit
68
Q

How are diseases investigated in the environment?

A
  1. Location visit
  2. Sample collection
  3. Food source visit
  4. Sanctions

Microbiology (5 decks)

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