Epidemiology Flashcards
(48 cards)
Epidemiology
study of occurrence, distribution and frequency of a disease
Why is epidemiological work carried out
to identify the source, how the disease spreads, ton introduce new prevention strategies
What type of data does epidemiological work contain
Theoretical and observational
Epidemeioloy og the infectious disease considers
source, transmission and susceptible person
Incidence
the rate at which people are getting sick.
tells us how fast a disease is spreading.
Prevalence
tells us how widespread the disease is at a specific time — it includes new and old cases.
tells us How many people are currently sick?”
No of cases can reduce in population even with new cases occuring. Why?
people dying
More cases may occur which are not new cases
re-infection
Epidemiolgical triad consists of
It has 3 parts that interact to cause disease:
agent- microorganisms
host- the susceptibility of getting a certain disease . factors such as working in healthcare, age, sex can affect the host
environment- everything around the host and agent that makes disease more or less likely e.g. overcrowding can increase the risk of getting pneumonia in children
What’s the disadvantage of epidemiological triad
doesnt consider vector diseases like malaria
Endemic
Disease is always present in a population, at a stable level.
It’s normal for it to be there.
Example: Malaria in parts of Africa, or chickenpox in school kids (before vaccines).
Hyperendemic
Disease is always present, but at a higher-than-usual level for that area.
More common than expected — but still consistent over time.
Sporadic
Disease occurs rarely and unpredictably.
Just a few cases, no pattern.
Epidemic
A sudden increase in cases, more than expected, in a certain area.
Can be big or small, but it’s unusual and fast.
Outbreak
Like an epidemic, but usually smaller and more local.
Can be in a school, town, or hospital.
Cluster
A group of cases in a specific time/place, but not always more than expected.
Pandemic
An epidemic that has spread across countries or continents.
Global in scale.
Example: COVID-19, 1918 Spanish flu.
How does a disease become an epidemic
Shift in agent, host or environment can change the level of the disease
How does a shift in agent change the level of the disease?
changes in pathogen itself can increase virulence, infectivity and transmission.
1- E.g. V.cholerae can become pathogenic when it acquires the CTX gene, which encodes a cholerae toxin. This transforms a harmless strain into pathogenic strain
2- Expanded host range : e.g SARS-COV2 likely evolved through mutations allowing it to pass from animals to humans illustarting zoonotic shift
How does a change in host factor changes the level of a disease
Changes in human behaviour or biology can increase vulnerability
1- for example increased travelling - e.g. travelling to south-africa may increase the risk of developing malaria
2- Immunocompromised inviduals are more susceptible to disease caused by opportunistic pathogens
How do environmental factors change the level of a disease
e.g. flooding or conditions which alter host susceptibility
🔄 Environmental Change: Mutation + Human-Animal Contact (Zoonosis)
Suddenly:
A new strain of influenza virus mutates in a pig or bird (like H1N1 or avian flu).
Due to deforestation, crowded live animal markets, or climate shifts, humans come into close contact with infected animals.
The new virus can now infect humans and spread between them — but no one has immunity.
Epidemics are classed by how they spread. What are 4 ways they spread?
1- Common source - all cases arise from the same source
Divided into point, continuous and intermettent
2- Propagated - spread person-person
3- Mixed - arise from the same common source then spread between person to person
4- Others including vector borne- spreads by mosquitoes
zoonotic - spreading from animals to humans
How is the spread of disease measured?
R0 value - basic reproduction number - tells us how contagious the disease is (R₀ is the average number of people that one sick person will infect in a completely susceptible population (meaning no one has immunity, and no public health measures are in place).
If R0>1 = disease spreads quicly, more people get ill.
R0<1= disease eventually disappears
R0= 1 = disease stays steady
R value
current measure of how many people one sick person is likely to infect right now.
The R value changes over time based on things like:
How many people are already immune (from vaccination or past infection).
How people are behaving (like social distancing, mask-wearing).
What health measures are in place (like lockdowns or travel restrictions).
If the R value is 3:
This means that on average, that 1 sick person will infect 3 other people in the next period of time
