Epidemiology tools notes

Incidence vs prevalence (worked examples):

• Incidence = new cases in a defined period. Example: a school reports 12 new flu cases during one week. Incidence for that week is 12.
• Prevalence = all existing cases at one point in time. Example: on Friday, 20 students currently have the flu (some got sick earlier). Prevalence on Friday is 20.
• Memory hook: incidence is the faucet (new water in), prevalence is the water level in the tub (everyone still sick right now).

Line list:

• A table where each row is one case and each column is a piece of information: case ID, onset date, symptoms, location, exposure. It is the raw data everything else is built from.

Epidemic curve shapes (what each tells you):

• Point-source: one sharp peak, everyone exposed at about the same time and place (like one contaminated meal).
• Continuous common-source: a plateau, the source keeps exposing people over time (like an ongoing water contamination).
• Propagated: a series of rising peaks, person-to-person spread across generations of cases.

Spot map:

• Plot each case at its location. A tight cluster around one point suggests a common exposure source nearby, like a single water pump or food vendor.