Health Protection and Communicable Disease Control
Core concepts
Understand the chain of infection (agent, reservoir, portal of exit, mode of transmission, portal of entry, susceptible host) and how interventions break each link. Know the main transmission routes - contact, droplet, airborne, vector-borne, foodborne, bloodborne, vertical - and the corresponding precautions. Be fluent in incubation periods, infectious periods, basic reproduction number (R0), effective reproduction number (Rt), and herd immunity threshold (roughly 1 − 1/R0).
Surveillance and control
Know the purposes of surveillance (detect outbreaks, monitor trends, evaluate interventions), the difference between passive and active surveillance, and notification requirements. Understand outbreak investigation steps: verify diagnosis, define cases, describe by person/place/time, generate hypotheses, test them, implement control, communicate. Recognise epidemic curves (point source, propagated, continuous common source) and what each implies.
Specific disease control
Know vaccine types and schedules conceptually, the principles of immunisation programmes, antimicrobial stewardship, and infection prevention and control (hand hygiene, isolation, PPE). Be aware of the legal and ethical framework for public health powers (notification, exclusion, contact tracing) balanced against proportionality.
Traps
Confusing isolation (of cases) with quarantine (of contacts); assuming R0 is fixed (it is context-dependent); misreading an epidemic curve's peak to infer transmission route; and forgetting that herd immunity thresholds rise steeply as R0 increases.
Rule of thumb
For R0 = 4, herd immunity threshold = 1 − 1/4 = 75% - meaning 75% of the population must be immune to stop sustained transmission.