Epidemiology

• Epidemiology involves:– determining etiology of infectious disease– reservoirs of disease– disease transmission – identifying patterns associated with outbreaks – outlining diagnostic tools and treatment options

– Incidence

– Prevalence

– Endemic

– Epidemic

– Pandemic

• In order for disease to spread:– Pathogen must have reservoir– Pathogen must be transmitted to susceptible

host

• Reservoirs of infectious disease:– Humans– Non-human animals– Environmental (non-living)

• Recognizing reservoir can help protect population from disease

• Human reservoirs– Infected humans most significant reservoirs

• If only reservoir disease is easier to control• Symptomatic or Asymptomatic carriers

• 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 levels could lead to reemergence of

disease• Small pox

• Reduction and eradication of disease– Some success

– 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)

– Notifiable Diseases

• World Health Organization (WHO)

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