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Unit 8: Epidemiology and Disease Transmission - Coggle Diagram
Unit 8: Epidemiology and Disease Transmission
Epidemiology
Rate of disease is more important than the number of cases
Attack rate - proportion of people who get sick after exposure
Incidence rate - number of new cases/time/population
Prevalence - total number of cases at any time or for a specific period in a given population
Study of disease patterns in populations
Communicable diseases
Spread from host to host
Non-communicable
Legionnaire's disease (does not spread from host to host)
Terms
Morbidity - burden of disease in population at risk
Mortality - overall death rate in population
Case-fatality rate - % of population that dies from a specific disease
Rates of disease
Endemic disease - constantly present in population
Outbreak - higher than expected cluster of disease cases over a specific time in a population
Epidemic - unusually large number of cases - over a larger region
Pandemic is a global epidemic
Outbreak epidemiology
Common source epidemic/outbreak
Rapid rise in cases - suggests exposure to single source of pathogen ex food poisoning
Propagated epidemic
Slow rise in cases --> contagious disease spreading in population
Study methods
Analytical studies
Determine relevancy of risk factors from descriptive study
Cross-sectional studies: surveys range of people at single point in time for absence/presence of disease
Retrospective studies: actions and events following outbreak compared
Prospective studies: looks ahead from prospective studies
Descriptive studies
Experimental studies
Modes of disease transmission
Pathogen factors that influence the epidemiology of a disease
Virulence
Ability to cause disease and how severe
Dose
Minimum amount of pathogens required
Incubation period
Influences extent of spread
Reservoirs
Human reservoirs
Symptomatic or asymptomatic infections
Non-human animal reservoirs
Zoonoses
Environmental reservoirs
Hard to eliminate
Vertical transmission - pregnant woman to fetus
Horizontal transmission - person to person
Direct or indirect contact (fomites)
Droplet transmission
Food and water, cross-contamination
Vectors (mechanical or biological)
Host factors that influence the epidemiology of a disease
Immunity to pathogen
General health
Age
Religious and cultural practices
Gender
Genetic background
Communicable disease epidemiology and modeling
Communicable vs non-communicable diseases
Communicable diseases are transmissable
Current cases produce future cases with communicable diseases
Epidemic models
Phenomenological
Describe epidemics without seeking to reproduce mechanisms
Compartmental
Describe disease as 'flow' of infection between compartments, with feedback loops
Deterministic
Get the same results every time
Agent-based
Model populations as individuals
Stochastic
Incorporate random chance
Terms
R0 (basic reproductive number)
Average number of secondary infections generated by a primary infection in a susceptible population
R0>1 --> epidemic grows
R0=1 --> disease stays endemic
Rt (effective reproduction number)
Average number of secondary infections generated by an infected individual at a given point in time
More realistic than R0
Epidemic model
Simplified representation of reality
Structured ways of thinking about a system
Available knowledge + plausible assumptions = logical implications
Allow to evaluate what-if scenarios to try to understand what might happen and help make decisions
Emerging infectious diseases
Zoonotic diseases are most popular
Emergence of disease
Antimicrobial resistance and polymicrobial diseases
Changes in human behaviour
Human environment
Currently emerging diseases
MERS coronavirus
Candida auris
Bloodstream infections
Resistant to most common class of antifungals (azoles)
Vibrio cholerae
Diarrhea through water supply