Epidemiology - Introduction
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Transcript of Epidemiology - Introduction
Epidemiology - Introduction
Study of patterns, distribution of disease (or other events)
•Cause/transmission
•Develop strategies for prevention
Epidemiologists, “health detectives”
Dr. Ignaz Semmelweis, Vienna (19th century), Puerperal fever
Epidemiology
• Principles of Epidemiology
• Epidemiological studies
• Infectious Disease Surveillance
• Trends in Disease
• Nosocomial Infections
Principles of Epidemiology
• Rate of Disease in a population
• Reservoirs of Infection
• Transmission
• Influential Factors
Rates of Disease in a Population
Endemic - disease constantly present in a particular geographic area
Epidemic - disease with an unusually high occurrence
Pandemic - worldwide severe epidemic
Morbidity - illness (morbidity rate)
Mortality - death (mortality rate)
Rate vs. Absolute number
Outbreak– cluster of cases occurring during a brief time interval and affecting a specific population.
Spread/prevention of disease
Reservoir
Natural habitat
Transmission
Reservoirs of infectious agents
•Human reservoirsSymptomatic
Asymptomatic carriers
•Non-human animal reservoirs
Reservoir
Natural habitat
Transmission
ex. cold virus
ex. Neis. gon.,
poultry - Salmonella, Campylobacter
**humans only reservoir - easiest to control**
Staph. aureus
Reservoirs of infectious agents
•Human reservoirsSymptomatic
Asymptomatic carriers
•Non-human animal reservoirs
Reservoir
Natural habitat
Transmission
ex. cold virus
ex. Neis. gon,
poultry - Salmonella, Campylobacter
rodents - Yersinia pestis
bats and racoons - rabies virus
**humans only reservoir - easiest to control**
Staph. aureus
Reservoirs of infectious agents
•Human reservoirsSymptomatic
Asymptomatic carriers
•Non-human animal reservoirs
Reservoir
Natural habitat
Transmission
ex. cold virus
ex. Neis. gon,
poultry - Salmonella, Campylobacter
rodents - Yersinia pestis
bats and racoons - rabies virus
**humans only reservoir - easiest to control**
**animal reservoir - difficult to control**
Staph. aureus
Reservoirs of infectious agents
•Human reservoirs
Symptomatic
Asymptomatic carriers
•Non-human animal reservoirs
Zoonoses/zoonotic diseases
•Environmental reservoirs
Reservoir
Natural habitat
Transmission
ex. cold virus
ex. Neis. gon,
poultry - Salmonella, Campylobacter
rodents - Yersinia pestis
bats and racoons - rabies virus
- diseases of animals transmitted to humans
**humans only reservoir - easiest to control**
**animal reservoir - difficult to control**
soil - Clostridium species
Staph. aureus
Transmission
Horizontal (person to person)
•contactdirect contactindirect contact
fomite
droplet
-inanimate object, such as clothing, doorknob and so on
Vertical (mother to fetus) Reservoir
Natural habitat
Transmission
Importance of hand washing
Large microbe-laden respiratory droplets generally fall to the ground on fartherthan 3 feet.
Importance of covering mouth when cough or sneeze
Transmission
horizontal
•contactdirect contactindirect contact
fomite
droplet
•food and water
•air
•vectors
Reservoir
Natural habitat
Transmission
- inanimate object
very difficult to control
flea - Yersinia pestis
mosquito - Plasmodium species (malaria)
vertical
arthropods
“Black Death” (Plague) - Yersinia pestis
fleaBubonic plague
Killed 1/4 of the population of Europe between 1346 - 1350; 75% of the population in some cities.
•Flea transmits Y. pestis to a human
•Multiplying bacteria spill into bloodstream (septicemic plague); endotoxin shock, DIC
•Bubo develops within days
•Bacterium is carried to a lymph node.
•50 - 75% mortality (if untreated)
•Y. pestis begins interfering with the inflammatory response - “arms itself”
rodent rodent
flea
flea
Influential Factors
• Dose There are few if any infections for which immunity
is absolute.
• Incubation Period
• Population Characteristics Immunity, General Health, Age, Gender,
Genetic Background
Epidemiological studies
•Descriptive studies
•Analytical studies
•Experimental Studies
Which risk factors were/are most relevant?
Person
PlaceTime
Risk factors
Epidemiological studies
•Descriptive studies
Person
Place
Time
Person
•Descriptive studies
Person
PlaceTime
Epidemiological studies
Epidemiological studies
•Descriptive studies
Person
PlaceTime
12
1. Rapid rise of sick people2. Gradual rise
Experimental studies
• Placebo
• Double-blind
Experimental studies are done mostly to assess the value of a particular interventionor treatment, such as antimicrobial drugtherapy.
Rates of Disease in a Population
Endemic
Epidemic
Pandemic
Morbidity
Mortality
Rates of Disease in a Population
Endemic - disease constantly present in a particular geographic area
Epidemic - disease with an unusually high occurrence
Pandemic - worldwide severe epidemic
Morbidity - illness (morbidity rate)
Mortality - death (mortality rate)
Infectious Disease Surveillance
CDC - National Centers for Disease Control and Prevention
MMWR - Morbidity and Mortality Weekly Report
WHO - World Health Organization
Weekly Epidemiological Record
Trends in Disease
• Reduction & Eradication of Disease
• Emerging Diseases
Trends in Disease
• Reduction & Eradication of Disease
- Improved sanitation
- Reservior & vector control
- Vaccination
- Antibiotic treatment
(Smallpox, eradicated globally)
Trends in Disease
• Emerging Disease - Microbial Evolution, drug-resistance strain
- Population expansion
- Mass distribution & importation of food
- Climate change
Nosocomial Infections(hospital-acquired infections)
5-6% patients, $4.5 billion cost
Enterococcus species. Part of the normal intestinal flora urinary, wound & blood infections Escherichia coli. Part of the normal intestinal flora Most common cause nosocomial urinary infection Pseudomonas species. Grow in moist environment
Staphylococcus species. Normal skin flora Common cause of nosocomial pneumonia and surgical site infection
Epidemiology
• Principles of Epidemiology
• Epidemiological studies
• Infectious Disease Surveillance
• Trends in Disease
• Nosocomial Infections