Transcript 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
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Principles of Epidemiology
Epidemiological studies
Infectious Disease Surveillance
Trends in Disease
Nosocomial Infections
Principles of Epidemiology
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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)
Rate vs. Absolute number
Mortality - death (mortality rate)
Outbreak– cluster of cases occurring during a brief time interval and affecting a specific population.
Spread/prevention of disease
Transmission
Natural
habitat
Reservoir
Reservoirs of infectious agents
•Human reservoirs
Symptomatic ex. cold virus
Transmission
Natural habitat
Reservoir
Asymptomatic carriers ex. Neis. gon., Staph. aureus
**humans only reservoir - easiest to control**
•Non-human animal reservoirs
poultry - Salmonella, Campylobacter
Reservoirs of infectious agents
•Human reservoirs
Symptomatic ex. cold virus
Transmission
Natural habitat
Reservoir
Asymptomatic carriers ex. Neis. gon, Staph. aureus
**humans only reservoir - easiest to control**
•Non-human animal reservoirs
poultry - Salmonella, Campylobacter
rodents - Yersinia pestis
bats and racoons - rabies virus
Reservoirs of infectious agents
•Human reservoirs
Symptomatic ex. cold virus
Transmission
Natural habitat
Reservoir
Asymptomatic carriers ex. Neis. gon, Staph. aureus
**humans only reservoir - easiest to control**
•Non-human animal reservoirs
poultry - Salmonella, Campylobacter
rodents - Yersinia pestis
bats and racoons - rabies virus
**animal reservoir - difficult to control**
Reservoirs of infectious agents
Transmission
•Human reservoirs
Natural habitat
Reservoir
Symptomatic ex. cold virus
Asymptomatic carriers ex. Neis. gon, Staph. aureus
**humans only reservoir - easiest to control**
•Non-human animal reservoirs
poultry - Salmonella, Campylobacter
rodents - Yersinia pestis
bats and racoons - rabies virus
**animal reservoir - difficult to control**
Zoonoses/zoonotic diseases - diseases of animals transmitted to humans
•Environmental reservoirs
soil - Clostridium species
Transmission
Horizontal (person to person)
Vertical (mother to fetus)
•contact
direct contact
indirect contact
Transmission
Natural habitat
Reservoir
fomite -inanimate object, such as clothing, doorknob
and so on
Importance of hand washing
droplet
Large microbe-laden respiratory droplets generally fall to the ground on farther
than 3 feet.
Importance of covering mouth when cough or sneeze
Transmission
horizontal
vertical
•contact
direct contact
indirect contact
fomite - inanimate object
droplet
•food and water
•air very difficult to control
•vectors arthropods
flea - Yersinia pestis
mosquito - Plasmodium species (malaria)
Transmission
Natural habitat
Reservoir
“Black Death” (Plague) - Yersinia pestis
Killed 1/4 of the population of Europe between 1346 - 1350; 75% of the population in some
cities.
Bubonic plague
flea
flea
•Flea transmits Y. pestis to a human
•Bacterium is carried to a lymph
node.
•Bubo develops within days
•Y. pestis begins interfering with the
inflammatory response - “arms itself”
rodent
rodent
flea
•Multiplying bacteria spill into bloodstream (septicemic plague);
endotoxin  shock, DIC
•50 - 75% mortality (if untreated)
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
Risk factors
Person
Place
Time
•Analytical studies
Which risk factors were/are most relevant?
•Experimental Studies
Epidemiological studies
•Descriptive studies
Person
Place
Time
Epidemiological studies
•Descriptive studies
Person
Place
Time
Epidemiological studies
•Descriptive studies
Person
Place
Time
1. Rapid rise of sick people
2. Gradual rise
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Experimental studies
Experimental studies are done mostly to
assess the value of a particular intervention
or treatment, such as antimicrobial drug
therapy.
• Placebo
• Double-blind
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
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Principles of Epidemiology
Epidemiological studies
Infectious Disease Surveillance
Trends in Disease
Nosocomial Infections