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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
What is a common source epidemic?
Rapid rise and fall of incidence | Arises from a single source e.g food poisoning/legionnaire's disease
26
What is a propagated epidemic?
Slow rise and fall of incidence Disease may be transmitted from each contaminated individual e.g strep throat
27
What is an opportunistic infection?
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
28
Example of opportunistic infections
Common in AIDS M.tuberculosis Herpes simplez virus
29
Meaning of eradication
Termination of all transmission of infection by extermination of infectious agent Through surveillance and containment
30
Meaning of elimination
Eradication of disease in a large geographic area
31
What diseases are currently easily eliminated?
Polio,measles, diphtheria
32
What is the attack rate?
Proportion of non-immune exposed individuals who become clinically ill
33
What is a primary and second case?
Primary case= person who comes into and jnfects population secondary case= those that subsequently contract the infection further spread= waves/generations
34
What is the reproductive rate/number (R)?
Average number of new infections caused by 1 infected individual
35
Meaning of R0?
Basic reproductive rate in an entirely susceptible population
36
What is the effective reproductive rate in a population where <100% are susceptible?
R= proportion susceptible x R0
37
What does it mean if R0>1?
Infection spreads (epidemic)
38
What does it mean if R0=1?
Infection remains constant (endemic)
39
What does it mean if R0<1?
Infection dies out
40
Determinants of R0 formula
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
What is the mathematical SIR model
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
Assumptions of SIR model
Latent period= 0 population is fixed- no births/deaths Infectious period= duration period After recovery, individuals are immune
43
Parameters needed to use model
effective contact rate, natural mortality rate, recovery rate, and disease-induced death rate
44
What are the 3 different types of reservoirs?
Human- look at diagram Animal Non-living
45
What is 'case'?
A person in the population/study group identified as having the particular disease/health condition/disorder/condition under investigation
46
What is a 'carrier'?
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
How does someone become a carrier?
Inadequate treatment/immune response | disease is not completely eliminated
48
What are the 3 elements that form a carrier state?
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
What can act as a reservoir of infection?
1. Soil- can harbor agents that cause anthrax, tetanus | 2. Inanimate matter
50
DIfferent modes of transmission
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
Meaning of a susceptible host
An infectious agent seeks a susceptible host to aim for successful parasitism
52
What 4 stages are required for successful parasitism?
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
Meaning of virulence
Degree of pathogenicity
54
How is virulence numerically expressed?
ratio of number of cases: total number infected | determined by immunoassay (measures concentration of antibody in body)
55
Meaning of case fatality rate?
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
Meaning of serial interval (generation time)
Gap in time between the onset of the primary and secondary cases Interval between recipient of infection and maximal infectivity of host
57
What is the infectious period?
length of time a person can transmit disease
58
What is the incubation period?
Time interval between invasion by infectious agent and appearance of first sign/symptom of disease
59
What is the latent period?
Period between being infected to becoming infectious
60
What is a transmission probability ratio (TPR)?
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
4 types of TPRs
p00 p01 p10 p11
62
p00
p00= tp from unvaccinated infective to unvaccinated susceptible
63
p01
p01= tp from vaccinated infective to unvaccinated susceptible
64
p10
p10= tp from unvaccinated infected to vaccinated susceptible
65
p11
p11= tp from vaccinated infected to vaccinated susceptible
66
How are diseases investigated in the clinic?
1. Collate symptoms 2. Foods eaten 3. Location foods eaten in 4. Secondary attacks
67
How are diseases investigated in the lab?
1. Preliminary culture 2. Attack rate analysis 3. Antibiotic analysis 4. definitive ID 5. Sample culture 6. Reference culture 7. Deposit
68
How are diseases investigated in the environment?
1. Location visit 2. Sample collection 3. Food source visit 4. Sanctions

Microbiology (5 decks)

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