• (the number of new cases of a disease occuring in a population during a specific time period)/(number of persons at risk of developing the disease during that period of time)

• (number of cases of a disease present in the population at a specified time)/(number of persons in the popuation at that specified time at risk)

• in America, the biggest public health problems we delt with around 1900 were infectious diseases
• now, the biggest public health problems consist of chronic noncommunicable diseases

• preclinical- not yet clinically manifested, but destined to progress to clinical disease
• subclinical- not clinically apparent and not destined to become clinical apparant
• chronic disease- individual fails to shake off disease and it persists for years at a time
• latent disease- infection with no active multiplication
• carrier- individuals harbor organism, but not infected while still can infect others
• reservoir- any person, animal, plant, soil, substance, or combo of these where infectious agent normally lives and depends on for survival and can multiply there

• host interacts with agent and environment
• envir. w/ agent and host
• agent w/host and envir.
• vector intersects all these

Used to study ID's

• contact
  • direct- skin, sex
  • indirect- infected fomite, blood, body fluid
• food and water born
• airborn (inhale contaminated air)
• vector born (depends on biology of vector and infectivity of organism)
• perinatal (during pregnancy)

• as far as getting infected with an ID, people vary in whether or not they get infected, the intensity of it, clinical outcomes, spatial distribution, and eve age

1. susceptibility of host
2. become infected (laten period)
3. become infective, and symptomotology will soon begin after
4. eventually, there is removal via immunity or death due to infection