Download Epidemiology

Epidemiology
• Epidemiological studies involve:
– determining etiology of infectious disease
– reservoirs of disease
– disease transmission
– identifying patterns associated with outbreaks
– outlining diagnostic tools and treatment options
– Morbidity rate
– Mortality rate
– Incidence
– Prevalence
– Endemic
– Sporadic
– Epidemic
– Pandemic
• In order for disease to spread:
– Pathogen must have reservoir
– Pathogen must be transmitted to susceptible
host
• Reservoirs of infectious disease can be
– Human
– Non-human animals
– Environmental (non-living)
• Recognizing reservoir can help protect
population from disease
• Human reservoirs
– Infected humans most significant reservoirs
• May be only reservoir which makes disease easier to control
• Asymptomatic carriers
– may shed organisms intermittently for long periods
• Non-human animal
reservoirs
– Zoonotic transmission
(zoonoses)
• Disease typically more
severe in humans
• Often accidental and
may be a dead end for
pathogen
• Environmental reservoirs
– 2 most important are
• Water
• Soil
• Transmission
– Successful pathogen must be passed from
reservoir to next susceptible host
• Contact
• Vehicle
• Vector
• Contact
– Direct contact
• Occurs when one person physically touches another
• Hands are the main source
– Indirect contact
• Transmission via inanimate objects or fomites
– Clothing, tissues, doorknobs and drinking classes
– Droplet transmission
• Respiratory droplets within three feet of release
• vehicle transmission
– Food, water and air
• Food contamination may originate with
animal or occur during food preparation
• Waterborne disease can involve large
numbers of people; prevention involves
proper sanitation
• Respiratory droplets dry; creates droplet
nuclei that may remain suspended or
become re-suspended
• Vectors
– Any living organism that can
carry a pathogen
• Most common are arthropods
• Mechanical or biological
– Control of vector-borne disease
directed at controlling arthropod
population
• Many disease occur in cycles
– May be annual or occur over decades
• Flu
• plague
• Herd immunity is an important factor in cycles
– Low level could lead to reemergence of disease
• Small pox
Epidemiological Studies
• Descriptive studies
– Person
• Determine profile of those who become ill
– Place
• Identifies general site of contact
• Give clues about potential reservoirs and vectors
– Time
• Rapid rise in numbers suggest common source
epidemic
• Gradual rise likely contagious
• John Snow
– identified common
source cause of cholera
epidemic
• Broad Street Pump in
London
– well-designed descriptive
epidemiological study
– years before the
relationship between
microbes and disease
was established
• Analytical studies
– Determines which potential factors from
descriptive study are relevant
• Experimental studies
– Judge cause and effect relationship of risk
factors or preventative factors
• frequently to determine effectiveness of prevention
or treatment
• Reduction and eradication
of disease
– Humans have been very
successful
– Efforts directed at:
•
•
•
•
Improving sanitation
Reservoir and vector control
Vaccination
Chemotherapy
– Why aren’t all infectious
diseases eradicated?
• Four mechanisms public health agencies
use to control disease transmission:
1. Isolation
2. Quarantine
3. Immunization
4. Vector control
Infectious Disease Surveillance
• National disease surveillance network
– Network of agencies across the country
• monitor disease development
– Agencies include
• Public Health Departments
• Centers for Disease Control and Prevention (CDC)
• World Health Organization (WHO)
• CDC
– National Dept. of Health
– Notifiable diseases
• Published data in weekly
publication
– Morbidity and Mortality Weekly
Report (MMWR)
• WHO
– International disease surveillance
• Weekly Epidemiological Record
• Provide global standards and guidance for human
health
Nosocomial Infections
• Hospital acquired
infections
– Range from mild to fatal
• Increased 36% in the last
20 years
– Leading cause of death
in the US
• 100,000 deaths per year
• Reservoirs of nosocomial pathogens:
– Exogenous
• Other patients
• Hospital environment
• Health care workers
– Endogenous
• Patient’s own normal flora
• Transmission of nosocomial pathogens:
– Medical devices
– Health care workers
– Airborne