Public Health, Epidemiology, and Communicable Disease Emergencies
Epidemiology basics
Understand incidence (new cases) vs. prevalence (all cases), attack rate, case fatality rate, basic reproduction number (R0), and herd immunity. Know surveillance types: passive, active, syndromic, and sentinel. A frequent trap: confusing incidence with prevalence-incidence measures new cases over time and is used to track an outbreak's trajectory.
Outbreak investigation
Know the steps: establish case definition, find cases, describe by person, place, time (epidemic curve), generate hypotheses, test hypotheses, implement control, and communicate. The epidemic curve shape suggests transmission mode (point source vs. propagated).
Communicable disease control
Understand isolation (separating ill) vs. quarantine (separating exposed, well), contact tracing, PPE and transmission-based precautions, and notifiable disease reporting. Know the role of public health authorities in declaring emergencies and issuing orders.
Risk communication
Apply risk communication principles: transparency, timeliness, consistency, and acknowledging uncertainty. The worried well can overwhelm healthcare; public messaging must direct them appropriately.
Rule of thumb: A single epidemic curve peak suggests a point-source exposure; a series of progressively taller peaks suggests person-to-person propagation.
Worked example: After a banquet, 40 of 200 attendees develop gastroenteritis within 12 hours. The attack rate is 40/200 = 20%. A single sharp peak on the epidemic curve supports a point-source foodborne exposure.