Epidemiology
description
Transcript of Epidemiology
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Epidemiology
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Epidemiology is:
• The study of the distribution and determinants of health-related states or events in specified populations and the application of this study to the control of health problems.
• Using data to answer questions of:• Who is getting sick?• What is making them sick?• How can we use this information to reduce the risk of
others getting sick?
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Disease surveillance• The ongoing systematic collection, analysis, and interpretation
of outcome-specific data for use in planning, implementation, and evaluation of public health practice.”
• Data collected in a surveillance system can be used for many purposes, including:– To estimate the magnitude of a health problem in a population– To understand the natural history of a disease– To detect outbreaks or epidemics– To document the distribution of a health event– To test hypotheses about causes of disease– To monitor changes in infectious organisms
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Epidemiology is:
• The study of disease at a population level– Endemic vs foreign disease– Sporadic vs epidemic vs pandemic– Disease outbreaks– Rate of disease– Incidence– Prevalence– Risk factors– Relative risk– Odds ratio
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Relative risk
• The risk of an event (i.e., developing a disease) relative to exposure
• A mathematical equation: RR = probability of disease occurring in
exposed individuals/ probability in non-exposed
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Odds ratio
• A measure of association: compares the odds of disease in those exposed to the odds of disease in those not exposed:
OR = odds of disease in exposed/odds of disease in non-exposed
• An OR of 1 = no difference between groups, so no association between hypothetical exposure/cause and outcome = illness
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Probability vs odds?
• The probability that an event will occur is the fraction of times you expect to see that event in many trials. Probabilities always range between 0 and 1.
• The odds are defined as the probability that the event will occur divided by the probability that the event will not occur.
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Association ≠ causation!!
• The causation fallacy
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Reservoirs
• Human reservoirs: symptomatic vs asymptomatic
• Non-human reservoirs• Environmental reservoirs
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Entry and exit strategies• Portal or entry• Portal of exit• Disease transmission:
– Direct contact• Fecal oral transmission• Sexual transmission
– Indirect contact• Fomites
– Droplet transmission– Air: droplet nuclei– Food– Vectors
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Vectors
• Mechanical vectors• Biological vectors
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Epidemiology of disease
Pathogen• Virulence factors• Dose• Incubation period
Host• Susceptibility to a specific
pathogen: receptors• Acquired immunity
– Active vs passive– Natural vs vaccination
• Herd immunity• General health status• Age• Genetics• Culture
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Types of epidemiologic studies
• Descriptive: who, what, where & when• Analytical– Cross sectional– Retrospective– Prospective
• Experimental• Molecular
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Cholera outbreak in Haiti 2010
• Identifying the source of the outbreak: a combination of analytical and molecular epidemiology
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Infectious disease surveillance
• National Disease Surveillance Network• International Society for Infectious Diseases:
ProMED: http://www.promedmail.org/• CDC: Morbidity and Mortality Weekly Report (MMWR): http://www.cdc.gov/mmwr/• Public health departments• WHO
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Emerging infectious diseases
• Novel diseases in a population OR diseases that have a recently increased incidence and/or distribution
• New vs newly recognized
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Emerging infectious diseases• Changes in microbes
– Microbial evolution: acquisition of virulence factors, antimicrobial resistance, evasion, invasion or exit strategies
– Expansion of microbial and vector distribution– Expansion of host range
• Environmental changes• Changes in hosts
– Complacency– Global travel– Population expansion– New forms of crowding together in small spaces (i.e., daycare
centers)
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Cryptococcus neoformans var. gattii• Increased incidence of cryptococcosis in healthy individuals• Spike in human cases preceded by a spike in canine cases
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Healthcare associated infections
• These come from:– Other patients– Healthcare environment– Healthcare workers– Patient’s own microbiota
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Infectious disease transmission in a health care setting
• Medical devices = fomites• Healthcare personnel = direct transmission• Airborne transmission