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
Virulence factors
Dose
Incubation period
Susceptibility to a specific pathogen: receptors
Acquired immunity
Active vs passive
Natural vs vaccination
Herd immunity
General health status
Age
Genetics
Culture

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:
CDC: Morbidity and Mortality Weekly Report
(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 neoformans var. 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