8. CPH Domain 5: Infectious Disease, Hazards, and ICS
After this lesson you can
- Place a hazard in one of five categories and distinguish hazard from risk
- Name the six links of the chain of infection and classify transmission as direct or indirect
- Calculate an outbreak attack rate and explain herd immunity and its link to R naught
- Assign prevention activities to the primordial, primary, secondary or tertiary level
- Work through the four-step risk assessment paradigm and the routes of exposure
- Describe the five ICS functional areas, span of control and where public health staff fit in a response
Video coming soon
Scheduled for release on November 23, 2026.
The first of two lessons on Domain 5, Disease and Injury Prevention, which carries 11 percent of the exam. It covers tasks 1, 2, 4 and 7: hazard identification, the chain of infection and modes of transmission, non-infectious environmental hazards and risk assessment, and emergency management with NIMS and the Incident Command System, built around a Harbor County flood.
Questions and answers
Questions a learner would ask about this lesson. Think through your own answer before you open each one.
- What is the difference between a hazard and a risk?
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A hazard is an agent or condition with the potential to cause harm. Risk is the probability that harm occurs, weighted by its consequence. A hazard with no exposure produces no risk, and the same hazard with different exposure carries a different risk.
- What is the difference between isolation and quarantine?
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Isolation separates people who are ill and infectious from those who are not. Quarantine separates and restricts the movement of people who were exposed but are well, and it lasts for the incubation period. Both may be voluntary or legally ordered, with the authority coming from Domain 4.
- How does herd immunity work?
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Herd immunity is the indirect protection susceptible people receive when enough of the population around them is immune, because chains of transmission break before they reach the few who are not. The threshold rises with the basic reproduction number, R naught, so highly contagious agents such as measles need very high coverage. The exam asks for the concept and the direction of the relationship, not the arithmetic.
- What are the steps of the four-step risk assessment paradigm?
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Hazard identification asks whether the agent can cause the harm at all. Dose-response assessment asks how the effect changes with dose. Exposure assessment asks how much people actually contact, by what route and for how long. Risk characterization combines the three into an estimate of risk and its uncertainty, and risk management is a separate decision that weighs cost, feasibility, law and values.
- Where does public health usually sit in the Incident Command System?
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ICS has five functional areas: Command, Operations, Planning, Logistics, and Finance and Administration. Public health usually staffs Operations, for example shelter health, water and food inspection, and medication dispensing, or Planning, where the epidemiologist produces the situation report. A communications officer often serves on the command staff as public information officer.
Practice quiz
- Question 1In the Harbor County flood shelter, 23 of 400 residents became ill. What is the attack rate, rounded?
- Question 2Immunization acts on which link in the chain of infection?
- Question 3Large droplets from a sneeze travel a short distance and fall quickly. This is classed as:
- Question 4A vector that hosts part of the agent's life cycle, rather than just carrying it, is a:
- Question 5Screening young children to detect elevated blood lead levels early is which level of prevention?
- Question 6A study measures how the frequency of a health effect changes as the amount of a solvent increases. Which risk assessment step is this?
- Question 7Which option appears first in the hierarchy of controls for occupational hazards?
- Question 8Which ICS section collects information, tracks status and writes the incident action plan?
- Question 9One shelter supervisor directs twelve staff members. How does this compare with the recommended span of control?
- Question 10In ICS, unity of command means:
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