Epidemiology Flashcards
1. Know what epidemiology is and its origins (i.e. Cholera and Snow) 2. Understand the three major aspects of Epidemiology, what is involved in each aspect, including the terms that we use to describe diseases and recommendations for controlling disease
What is epidemiology
epidemiology examines the distribution and prevalence of diseases in human populations
What individual is associated with the beginning of epidemiology
John Snow
John Snow (birth place and job)
- Born in Yorkshire, U.K. in 1813
- Pharmacist, surgeon, physician
- Lead the modernization of Anesthesiology
Vibrio cholera
- Causes Cholera
- Gammaproteobacteria
- Facultative aerobe
Where is Vibrio cholera commonly found
Aquatic environments: Fresh water and ocean
How does Vibrio cholera cause Cholera
Carries prophage encoding cholera toxin
* cholera toxin generates osmotic imbalance in intestinal lumen
* intestinal lining shlufs off causing diarrhea = more spread of disease
Symptoms of Cholera
Vomiting, severe diarrhea (8-15 L of liquid lost per day), black/blue discolored skin from ruptured capillaries
Incubation period and fatality rate of Cholera
incubation period = 1-5 days
without treatment, fatality rate = 25-50%
treatment = antibiotics and fluid
First outbreak of Cholera
1831 United Kingdom in the coastal town of Medway
* John snow was also first treating survivors after an outbreak at a local mine
What theory still persisted during the Cholera epidemics in the UK
Miasma theory: diseases were caused by the presence of bad air (a miasma)
1854 Cholera outbreak in central london
People drinking water from the Broad Street pump were getting sick with Cholera
* John Snow made this geographic discovery by conducting interviews at houses hit hardest by disease
Why did the Broad Street Brewery workers not get sick with Cholera
Water from the pump was being boiled to make the beer and the workers were only drinking beer
How was the 1854 Broad Street Cholera outbreak solved
authorities removed the pump handle so people could not get water from the pump
Over the years, John snow linked cholera with
sewage-contaminated water
* also wrote 1855 book, “Mode of Communication of Cholera” and his results were ignored for 35 years
Modern day example of Cholera epidemic
Haiti - 2010
Sewege for U.N camp was dumped in stream and contaminated water traveled down river (with rainfall) to infect people
* within 7 days it became a full blown epidemic
* within a month the outbreak spread to all regions of Haiti
* In 2011, rains and flooding led to resurgences
Three major aspect of epidemiology
- Occurence and distribution of disease
- Determinants of disease
- Recommendations for control of disease
Components that make up occurence and distribution of disease
- data collection and analysis
- modeling
- Classification
Three components of data collection for epidemiology
- incidence
- prevalence
- mortality
incidence vs. prevalence
incidence: number of new cases in a population per time period
prevalence: total cumulative # of infected individuals in a population (new and old cases of infection)
common graph lines of incidence vs. prevalance
incidence will peak and fall while prevalence will steadily climb
mortality
number of deaths per unit in a infected population
Incidence, prevalence, mortality?
SIR model
R naught model (R0)
basic reproduction number, a metric used to describe the contagiousness or transmissibility of infectious agents
Contagiousness
* H1N1 = 1.2-1.6
* COVID19 = 2-3
* Ebola = 1.6-2
* Measles = 12-18
What is R naught affected by
numerous biological, sociobehavioral, and environmental factors that govern pathogen transmission
Three ways to classify disease occurence
- endemic
- epidemic
- pandemic
endemic disease
a disease that is always present (in a given region) at a low frequence
often have local, natural reservoirs (e.g. animals, water) that harbor or carry the infectious agent
* Lyme disease
* Cholera
* Rabies
* Plague
* Flu
epidemic disease
A disease that is occuring at a higher than normal frequency
An endemic disease can become
epidemic - if the frequency shoots up
Endemic vs epidemic on a graph
Note the normal seasonal cycles and when it spikes up
How do epidemic disease arise
- increased in the animal reservoir (e.g. Plague)
- Increased interaction with reservoir (e.g. Cholera in water)
- Transfer from animal to human (e.g. HIV/AIDS) - zoonotic diseases
Common source vs propogated epidemics
and their defining characteristics
Common source epidemics: due to a shared common source (food, water)
* Peak level of infection in a short time
* Usually results from a single contaminated source
* E. histolytica - Chicago World’s Fair - contaminated drinking water
Propagated epidemics: due to host to host to host transmission
* Typically a slow and prolonged rise in # of cases
* Viruses - flu
Pandemic
An epidemic that occurs globally
An epidemic can become a pandemic if
it spreads globally
* can be short-lived (e.g. 1918 flue epidemic)
* Or last longer (e.g. plague, HIV/AIDs)
Recommendations for controlling disease spread
- Isolation/Distancing/Quarantine
* Limiting host-to-host transmission only (
* works best for more contagious diseases - Remove source
* common source or propagated epidemics
* removing pump handle (common), washing hands (propogated), throwing away contaminated food (common) - Increasing Herd immunity/Immunization
How does Herd immunity work
limits spread of infectious disease within a population that is based on pre-exisiting immunity of a high proportion of individuals due to previous infection or vaccination
* only applies to diseases that communicable (can be shared person to person)
R0 (R naught) and herd immunity
R naught affects what portion of the population needs herb immunity to prevent epidemics/widespread transmission
* >70% for less contagious pathogens
* ~95% for highly contagious pathogens
R naught and “Herd immunity threshold” of measles
Measles has the highest R naught and thus the highest Herd Immunity Threshold
