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

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 Epidemiological Studies

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