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Epidemiology

Epidemiology. 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?

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Epidemiology

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  1. Epidemiology

  2. 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?

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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.

  8. Association ≠ causation!! • The causation fallacy

  9. Reservoirs • Human reservoirs: symptomatic vs asymptomatic • Non-human reservoirs • Environmental reservoirs

  10. 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

  11. Vectors • Mechanical vectors • Biological vectors

  12. Epidemiology of disease Pathogen Host Susceptibility to a specific pathogen: receptors Acquired immunity Active vs passive Natural vs vaccination Herd immunity General health status Age Genetics Culture • Virulence factors • Dose • Incubation period

  13. Types of epidemiologic studies • Descriptive: who, what, where & when • Analytical • Cross sectional • Retrospective • Prospective • Experimental • Molecular

  14. Cholera outbreak in Haiti 2010 • Identifying the source of the outbreak: a combination of analytical and molecular epidemiology

  15. 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

  16. Emerging infectious diseases • Novel diseases in a population OR diseases that have a recently increased incidence and/or distribution • New vs newly recognized

  17. 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)

  18. Cryptococcus neoformansvar. gattii • Increased incidence of cryptococcosis in healthy individuals • Spike in human cases preceded by a spike in canine cases

  19. Healthcare associated infections • These come from: • Other patients • Healthcare environment • Healthcare workers • Patient’s own microbiota

  20. Infectious disease transmission in a health care setting • Medical devices = fomites • Healthcare personnel = direct transmission • Airborne transmission

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