Epidemiology

Question 1

What is epidemiology

Answer 1

epidemiology examines the distribution and prevalence of diseases in human populations

Question 2

What individual is associated with the beginning of epidemiology

Answer 2

John Snow

Question 3

John Snow (birth place and job)

Answer 3

• Born in Yorkshire, U.K. in 1813
• Pharmacist, surgeon, physician
• Lead the modernization of Anesthesiology

Question 4

Vibrio cholera

Answer 4

• Causes Cholera
• Gammaproteobacteria
• Facultative aerobe

Question 5

Where is Vibrio cholera commonly found

Answer 5

Aquatic environments: Fresh water and ocean

Question 6

How does Vibrio cholera cause Cholera

Answer 6

Carries prophage encoding cholera toxin
* cholera toxin generates osmotic imbalance in intestinal lumen
* intestinal lining shlufs off causing diarrhea = more spread of disease

Question 7

Symptoms of Cholera

Answer 7

Vomiting, severe diarrhea (8-15 L of liquid lost per day), black/blue discolored skin from ruptured capillaries

Question 8

Incubation period and fatality rate of Cholera

Answer 8

incubation period = 1-5 days
without treatment, fatality rate = 25-50%

treatment = antibiotics and fluid

Question 9

First outbreak of Cholera

Answer 9

1831 United Kingdom in the coastal town of Medway
* John snow was also first treating survivors after an outbreak at a local mine

Question 10

What theory still persisted during the Cholera epidemics in the UK

Answer 10

Miasma theory: diseases were caused by the presence of bad air (a miasma)

Question 11

1854 Cholera outbreak in central london

Answer 11

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

Question 12

Why did the Broad Street Brewery workers not get sick with Cholera

Answer 12

Water from the pump was being boiled to make the beer and the workers were only drinking beer

Question 13

How was the 1854 Broad Street Cholera outbreak solved

Answer 13

authorities removed the pump handle so people could not get water from the pump

Question 14

Over the years, John snow linked cholera with

Answer 14

sewage-contaminated water
* also wrote 1855 book, “Mode of Communication of Cholera” and his results were ignored for 35 years

Question 15

Modern day example of Cholera epidemic

Answer 15

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

Question 16

Three major aspect of epidemiology

Answer 16

1. Occurence and distribution of disease
2. Determinants of disease
3. Recommendations for control of disease

Question 17

Components that make up occurence and distribution of disease

Answer 17

• data collection and analysis
• modeling
• Classification

Question 18

Three components of data collection for epidemiology

Answer 18

• incidence
• prevalence
• mortality

Question 19

incidence vs. prevalence

Answer 19

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)

Question 20

common graph lines of incidence vs. prevalance

Answer 20

incidence will peak and fall while prevalence will steadily climb

Question 21

mortality

Answer 21

number of deaths per unit in a infected population

Question 22

Incidence, prevalence, mortality?

Answer 22

Question 23

SIR model

Answer 23

Question 24

R naught model (R0)

Answer 24

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

Question 25

What is R naught affected by

Answer 25

numerous biological, sociobehavioral, and environmental factors that govern pathogen transmission

Question 26

Three ways to classify disease occurence

Answer 26

• endemic
• epidemic
• pandemic

Question 27

endemic disease

Answer 27

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

Question 28

epidemic disease

Answer 28

A disease that is occuring at a higher than normal frequency

Question 29

An endemic disease can become

Answer 29

epidemic - if the frequency shoots up

Question 30

Endemic vs epidemic on a graph

Answer 30

Note the normal seasonal cycles and when it spikes up

Question 31

How do epidemic disease arise

Answer 31

• 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

Question 32

Common source vs propogated epidemics

and their defining characteristics

Answer 32

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

Question 33

Pandemic

Answer 33

An epidemic that occurs globally

Question 34

An epidemic can become a pandemic if

Answer 34

it spreads globally
* can be short-lived (e.g. 1918 flue epidemic)
* Or last longer (e.g. plague, HIV/AIDs)

Question 35

Recommendations for controlling disease spread

Answer 35

1. Isolation/Distancing/Quarantine
   * Limiting host-to-host transmission only (
   * works best for more contagious diseases
2. Remove source
   * common source or propagated epidemics
   * removing pump handle (common), washing hands (propogated), throwing away contaminated food (common)
3. Increasing Herd immunity/Immunization

Question 36

How does Herd immunity work

Answer 36

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)

Question 37

R0 (R naught) and herd immunity

Answer 37

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

Question 38

R naught and “Herd immunity threshold” of measles

Answer 38

Measles has the highest R naught and thus the highest Herd Immunity Threshold