epidemiology Flashcards
1
Q
Epidemiologists
A
- Study positive health states
- Discover agent of disease, environmental factors
- Determine patterns
- Identify segments of population at risk
Health programs or services to improve health
2
Q
Cholera 1800s vs 2020
A
- Better knowledge of outbreak
- Germ theory in early phase
- Widespread, high mortality vs ~200,000 deaths/yr.
- Water from Thames vs separate water supply
Not efficient sewage system vs efficient
3
Q
Epidemiological triangle
A
- Infectious agent - virus, bacteria, parasite etc.
- Host
○ Demographic factor - e.g. age, ethnicity
○ Biological and genetic factor - e.g. blood group, immunity
○ Behavioural and cultural - smoking, alcohol, diet - Environment
○ Physical, chemical, biological
○ Environment - geology, climate, vectors
Socioeconomic - occupation, income, access to services
- Host
4
Q
Pathogen - effect of dose
A
- Shorter incubation period when increased does of Salmonella
Incubation period - time from pathogen exposure to onset of signs and symptoms
5
Q
Risk
A
- Modifiable = potential to improve health
○ Usually environmental - climate change, agriculture, individual behaviours
Unmodifiable risk factors = less able to improve health - geneitic
6
Q
mortality vs morbidity
A
amount of death due to disease
amount of illness due to disease
7
Q
elimination vs eradication
A
reduction to zero in geographic location
complete and permanent reduction to zero
8
Q
Disease burden
A
- Measure of impact of living with disease
- Measure of gap between current health and ideal health
- Financial cost, morbidity, mortality
Measurement = disability- adjusted life years (DALYs) - years healthy life lost due to illness and death
9
Q
Prevalence
A
- Proportion of population with disease at specific time
- Snapshot
Number of ppl at a specific time with disease / total number of people in the population at risk
- Snapshot
10
Q
Incidence
A
- Number of new cases over a period of time
- Presented as proportion or rate measurement
Indication of infection risk with a specific time
- Presented as proportion or rate measurement
11
Q
Prevalence vs incidence
A
- Allows comparison among different populations
- Prevalence measures existing disease
- Incidence measure rate at which new cases occur
- If incidence increases, prevalence increases
- If prevalence is introduced (eg vaccine, quarantine), incidence will decrease
- If effective treatment is found, prevalence will decrease
12
Q
levels of outbreak
A
Pandemic - all
Epidemic - outbreak
Endemic - expected level
Sporadic - occurs infrequently
13
Q
sporadic level
A
occasional cases occurring at infrequent intervals (low level)
14
Q
endemic level
A
Persistent occurrence - baseline - low to moderate
15
Q
epidemic level
A
- Increase in expected level - can be rapid - large number of cases in short period
- Clusters
- Conditions
○ Agent +susceptible host in reasonable numbers
○ Change to infectious agent - increase in amount, fast incubation
○ New disease in naïve population
○ Mode of transmission
Opportunities for exposure - slow recognition
16
Q
pandemic level
A
- Over several countries
Large number of people
17
Q
Exposure
A
- Host and infectious agent encounter each other
- Possible outcomes
○ No infection
○ Death - clinical
○ Recovery + immunity - clinical
Immunity - subclinical
- Possible outcomes
18
Q
Incubation period
A
- 3-5 days average
- From exposure to sign
- Pathogen development but no clinical manifestations
- Length
○ Virulence
○ Host health
○ Site
Reproduction number
19
Q
Prodromal period
A
- Clinical manifestation
- Short period preceding illness
Can be contagious
- Short period preceding illness
20
Q
Incubation period useful for:
A
- Predict disease severity
○ Shorter incubation = more severe- Quarantine duration
Interpret public health surveillance data
- Quarantine duration
21
Q
Illness
A
- Onset of symptoms
- Most severe stage
Immune response still being formed
- Most severe stage
22
Q
Decline
A
- Returning to normal
- symptoms reduce
Or death
- symptoms reduce
23
Q
Convalescent period
A
- Recovery
Symptoms disappear
24
Q
The chain of infection - expanding infection triangle
A
- Source / reservoir
- Agent
- Transmission
- Portal of entry
- Susceptible host
Portal of exit
25
Source
location from which pathogen is transmitted to host
- Animate (humans, plant, animals)
○ Zoonosis (disease of animals transmitted to humans)
- Inanimate - soil, water, food, air
26
reservoir
normal habitat where pathogen is normally found
- Sometimes same as source (human carrier of TB)
- Sometimes different from source (Hendra virus)
○ Reservoir - bats
○ Source of human infection = horses
27
Direct or indirect by 4 main routes
- Airborne
- Contact
- Vehicle
Vector
28
Direct
- person to person - secretions, cells, air
- Zoonosis
Vertical transmission via placenta
29
Indirect
one host to another via intermediate (vehicles)
| Intermediate can be animate (e.g. mosquito) or non-living (e.g. Doorknob)
30
Airborne (Water droplets)
- Large respiratory droplets (5-10 micrometre diameter)
○ Singing, talking, coughing, sneezing
- Aerosols (1-5micrometre in diameter
○ Talking and breathing
○ Long time (hours to days)
Reservoirs - air conditioning cooling towers e.g. legionnaires
31
airborne (dust)
- Become airborne due to disturbance, survive long
- Fungal infections
Hospital acquired
32
Vehicles
- Surgical instruments
- Cosmetics
- Clothing
- Phones
- Food
- Soil
Blood products
33
Vector
- Insects - malaria
- Ticks - Lyme
- Fleas - plague
- External transmission - passive carriage on body surface - shigellosis
- Internal transmission - carried inside vector - malaria
34
Portal of entry
- Oral route - food borne, water borne
- Respiratory - dust, droplets
- Urogenital - genital
- Parenteral - injection to bloodstream - needles
- Conjunctival - surface of eyes
Dermal - skin - bite
35
primary vs index vs secondary case
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Primary case
- First case in population
Index case
- First case reported to authorities
Secondary
Cases resulting from subsequent transmission
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36
Reproduction rate (R0)
- Indicate how contagious the disease is
- R0 assumes population is completely vulnerable (no immunity, no vaccine)
- If R0 = 1, each infection causes one new infection
- If R0 <1, disease declines
- If R0 >1, disease increases, may result in outbreak
The larger R0 the more contagious
37
Re and R0 factors
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Re (effective) is used when there is some immunity or intervention measures
R0 = not measurement of time or severity
Factors
- Duration
- Infectivity
- No. of contacts
- Host factors - health
Climatic factors
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38
immunity
- The capacity of a person when exposed to an infectious agent to remain free of infection
- Can be acquired prior infection or immunisation
- Varies for different diseases
○ Measles- experience it once, immunity life long
Whooping cough - immunity can wain from previous infection
39
herd immunity
- Immunity of a group or community
- Resistance to infection of a high proportion of individuals of a group
- Resistance is a product of the number of susceptible people and the probability that those whose are susceptible will come into contact with an infected person
1-1/R0
40
Ten steps of treating an outbreak
1. Establish existence of outbreak
2. Research the disease, fieldwork
3. Verify diagnosis
4. Define and identify cases = case definition - speak to patients
5. Use descriptive epidemiology - who, what, when, where, why, how
6. Develop hypotheses
7. Evaluate hypotheses
8. Refine hypotheses
9. Implement control and prevention measure - prevent additional cases
10. Develop policies and communicate findings - health policies, education
