Epidemiology Flashcards
(37 cards)
what is epidemiology
= the study of the distribution and the causes of health-related states and events in specified populations, and the application of this study to help control health problems
what are examples of public health problems/ events that are investigated by epidemiologists
- environmental exposures
- infectious diseases
- non-infectious diseases: spread of a type of cancer, increase in birth defect
- injuries/ crime: increased homicides, rise in domestic violence
- terrorism
- natural disasters
what is an outbreak/ epidemic?
= a sudden increase in cases of a particular disease in a given area or among a specific group of people/ period of time
What is a pandemic?
If a disease spreads over a continent or even the world
what is the meaning of endemic?
when a population has a high level of the disease present all the time
- example: giardiasis and even malaria are endemic in parts of the world
Why are epidemiologists called “disease detectives”?
they:
- investigate causes of disease
- who is at risk
- how it spreads
- how to control or prevent the spread
- what are symptoms
through:
- data collection
- making connections…
What is the epidemiological triangle?
= a model that scientists have developed for studying health problems.
It can help you understand infectious diseases and how they spread.
The Triangle has three corners (called vertices):
- Agent, or microbe that causes the disease (the “what” of the Triangle)
- Host, or organism harboring the disease (the “who” of the Triangle)
- Environment, or those external factors that cause or allow disease transmission
(the “where” of the Triangle)
What do epidemiologists want to do to the triangle
The mission of an epidemiologist is to break at least one of the sides of the Triangle, disrupting the connection between the environment, the host, and the agent, and stopping the continuation of disease
What could the “agent” be?
= the cause of the disease; usually a microbe for infectious diseases
Germs:
- bacteria: single-celled, reproduce by themselves, larger than viruses, often move with a flagellum
- virus: have a core of genetic material, but need a host to reproduce –> use the reproductive machinery of cells
- fungi: cannot produce their own food so aren’t like plants, e.g. mushrooms & yeast
- protozoa: very small, most live in water, are parasites –> live off other organisms, e.g. malaria & giardia
What could the “host” be?
= organisms, usually humans or animals, which are exposed to and harbor a disease.
- can be the organism that gets sick
- can be any animal carrier (including insects and worms) that may or may not get sick
- experiences symptoms
- or carries it without knowing it
What could the “environment” be?
= the favorable surroundings and conditions external to the host that cause or allow the disease to be transmitted
e.g.:
- dirty water
- human blood
- season of the year & temperatures
Who was John Snow and what did he do?
= the father of epidemiology
He discovered the real cause of cholera:
–> that it is spread through contaminated water rather than airborne
What is an environmental disease?
= diseases that can be directly attributed to environmental factors (as distinct from genetic factors or infection)
Apart from the true monogenic genetic disorders, which are rare (alterations in a single gene, like sickle-cell anaemia), environment is a major determinant of the development of disease.
- Diet
- exposure to toxins
- pathogens
- radiation
- chemicals found in almost all personal care products and household cleaners
- stress
- racism & physical + mental abuse
= causes of a large segment of non-hereditary disease
What are systemic diseases?
= disease that affects a number of organs and tissues, or affects the body as a whole
What are categories of disease?
Infectious
e.g.: cholera, malaria, HIV, tuberculosis
Non-infectious:
- deficiency
- inherited
- mental disorders
e.g.: cancers, COPD, sickle-cell anaemia, cystic fibrosis
Degenerative
know cholera, malaria, HIV and tuberculosis as examples
Cholera:
- vibrio cholerae
- wall of small intestine
- water and foodborne
- diarrhoea, dehydration
Malaria:
- plasmodium (parasite, 4 types)
- transmission: insect vector (mosquito)(host) & blood transfusion, unsterile needles
- fever, headaches, muscle pain, shivering, enlarged spleen
HIV/AIDS:
- retrovirus HIV (RNA not DNA as genome)
- targets T-helper cells, macrophages, brain cells
- unable to survive outside of the body
transmitted through:
- sexual intercourse
- shared unsterile needles
- blood donation
- mother to child, through breast milk or during pregnancy
- flu-like symptoms, opportunist infections
TB:
- bacteria
- airborne droplets & contaminated dairy products
- cough, chest pain, coughing blood, fever, diarrhoea, weight loss…
Was the eradication of smallpox or of AIDS more successful? Why?
AIDS: more difficult
- infected person can remain symptomless for years (HIV virus is dormant), making it hard to identify and target
- mutates very quickly
–> escapes antigen detection
–> harder to develop vaccine
- targets helper T-cells
–> difficult to treat: central component of IS
SMALLPOX: has been eradicated
- clearly visible & identifiable symptoms
- stable –> easy to develop vaccine
What factors influence infection & its spread in a population?
- virulence = the degree of damage caused by the pathogen to the host & its ability to cause disease
- duration of infection –> longer the infectious phase, more risk of contamination
- rate of transmission
How are mathematical models used to help with disease outbreaks?
- to project and predict how it will progress
- to show the likely outcome
- to help inform the public of health interventions necessary
what is the SIR model and what does it model?
represents 3 groups of people:
- suceptible: not infected yet but at risk
- infected: currently infected and infectious
- removed: were already recovered & either died, or recovered + gained immunity
What is the reproductive number R0 in SIR model?
= dictates the relationship between the 3 parameters: S, I, R
R0: the average number of ppl who will get infected from 1 infected person
–> varies depending on virulence of pathogen
–> applies to a population that isn’t immune
R0 >1 –> disease spreads, results in outbreak
R0 <1 –> disease declines, eventually dies out
R0 =1 –> endemic
R0 is greater is less people are immune
R0 is smaller through vaccines and recovery
How is R0 calculated?
How is the prob. of transmission calculated?
R0 = C x P x D
C: contact rate per day
P: probability of transmission between infected + uninfected people
D: infectious period, where you are contagious
P = x/n
x: number of people that got infected by people who were previously infected
n: total number of susceptible people in the group
What is the effective reproductive number, Rt or Re?
= the number of cases generated in the currengt state of a population, not necessarily an uninfected state
= the average number of new infections caused by a single infected individual at a certain time (t) in a partially susceptible population
How is Rt calculated?
What is it’s connection to HERD IMMUNITY?
Rt = R0 x S
S: the fraction or % of the population that’s susceptible
when Rt drops below 1, herd immunity has been achieved, and the number of cases will gradually decrease to 0
