Microbiology Lect 22 Flashcards
Epidemiology
Examines the distribution and prevalence of diseases in human populations
How did Epidemiology start?
-John Snow treated survivors of a cholera outbreak in 1831
-1854 cholera outbreak in London, John Snow conducted interviews of houses hardest hit by the disease
-Noticed cases/deaths were geographically clustered, and all had drawn water from the Broad Street pump
-Authorities removed the pump handle so people couldn’t get water
-Snow linked cholera with sewage-contaminated water
-Snow wrote a book in 1855, and his results were ignored for 35 year
Cholera
-Caused by Vibrio cholera
-class Gammaproteobacteria, faculative aerobe
-Carries a prophage encoding cholera toxin, which generates osmotic imbalance in intestinal lumen
-Sympotms: vomiting, severe diarrhea (8-15 L of liquid lost perday)
-Incubation period of 1-5 days
-Without treatment, fatality rate: 25-50%
Modern Cholera epidemic Haiti
-Sewage from UN camps was dumped above a stream, and it rained
-People from the camp first got sick, then it spread to the city and all regions of Haiti
-Rain caused a resurgence a year later
Three major aspects of Epidemiology
-Occurrence and distribution of disease
-Determinants of disease
-Recommendations for control of disease
Steps of Occurrence and Distribution of Disease
-Data collection and analysis
-Modeling
-Classification
Data collection and analysis
-Incidence: number of new cases in a population per time period
-Prevalence: total cumulative number of infected individuals in a population
-Mortality: number of deaths per unit time in an infected population
Modeling (Steps of Occurrence and Distribution of Disease)
-SIR model
-Models also used to estimate R0
SIR model
-S: susceptible
-I: infected
-R: recovered/dead
R0
-Basic reproduction number, a metric used to determine the contagiousness or transmissibility of infectious agents
-Affected by numerous biological, sociobehavioral, and environmental factors that govern pathogen transmission
-Estimated with various types of mathematical modes
-Basically says how many people one infected person will infect
Classification (Steps of Occurrence and Distribution of Disease)
-Endemic
-Epidemic
-Pandemic
Endemic
-A disease that is always present (in a govern region) at a low frequency
-Often have local, natural reservoirs (animals, water, etc) that harbor or carry the infectious agent
-Ex: Rabies, plague, cholera, lyme disease
Epidemic
-A disease that is occurring at a higher than normal frequency
-Endemic can become endemic due to an increase in reservoir, interaction with the reservoir, or transfer from animals to humans
Common Source Epidemic
-Due to a shared common source (ex: food, water)
-Peak levels of infection in a short period of time
-Usually results from a single contaminated source
Propagated epidemics
-Due to host-to-host transmission
-Takes longer to reach the peak and stop the epidemic
