Communicable Disease Prevention and Control
Core concepts
Communicable disease control requires surveillance, case definitions, notification, outbreak investigation, and rapid response. Know transmission routes, incubation and latent periods, infectiousness, basic reproduction number, effective reproduction number, and herd-immunity threshold. Distinguish isolation of cases from quarantine of contacts, and chemoprophylaxis from treatment. Understand contact tracing, ring vaccination, cold-chain management, infection prevention and control, antimicrobial stewardship, and the epidemiology of tuberculosis, HIV, malaria, dengue, measles, and polio. Outbreak investigation proceeds through verification, case definition, descriptive analysis, hypothesis generation, analytic study, control measures, and communication.
Traps
Quarantine applies to exposed contacts; isolation applies to cases. Case fatality is not the same as attack rate or mortality rate. Herd-immunity threshold is 1−1/R0 only for a simple homogeneously mixing population. Vaccine efficacy is measured in trials; vaccine effectiveness is measured in real-world use. A long incubation period shapes quarantine duration. Notifiable disease reporting is a legal duty, not optional surveillance.
Worked example
If R0 for a measles-like infection is 5, the herd-immunity threshold is 1−1/5 = 0.80, or 80%, assuming perfect vaccine protection. If vaccine efficacy is 90%, the required coverage is 0.80/0.90 = 0.89, or about 89%. This illustrates why highly transmissible diseases demand very high coverage.
Rule of thumb
Break the chain at its weakest link: reservoir, mode of transmission, or susceptible host.