Source and agent CER
Thu, Nov 19, 2026 · Week 13 · Principles of Biomedical Technology (Principles of Biomedical Science)
Today's goal: Students write a CER identifying the likely source and infectious agent of the outbreak.
This is a model of the work you should turn in today. Use it to check your own: match the structure and the level of detail, do not copy it. Your data and wording should be your own.
This is a MODEL from a different case, not the answer to today's reunion outbreak. Study how the pieces fit together, then build your own argument from your own curve, map, and test.\n\nScenario (parallel case): Campers at a lakeside summer camp fall ill with watery diarrhea over one week. Investigators have an epidemic curve, a spot map of cases by cabin, and a water sample result. They must name a likely source and agent.\n\nClaim: The likely source of the outbreak was untreated water from the camp's shallow well, and the likely agent was a waterborne protozoan parasite (Giardia).\n\nEvidence (three independent sources):\n- Epidemic curve: cases rose gradually and stayed elevated for about a week, a continuous-source pattern rather than one sharp peak.\n- Spot map: cases were spread across cabins on the well-fed side of camp, not clustered around any single meal or event.\n- Agent ID: a water sample from the well tested positive for Giardia cysts, a parasite spread through contaminated water.\n\nQuantitative measure: Attack rate = (24 cases / 80 campers using the well) x 100 = 30 percent.\n\nReasoning: A continuous-source curve means people kept getting exposed over days rather than all at once, which fits ongoing use of a water supply instead of one shared meal. The map locates the exposure with the campers who drank from the well, and the water test names the organism. Each tool answers a different question (when, where, what), and only together do they point to one explanation. A single peak would have suggested a one-time source, so the shape of the curve matters as much as the map and the test.\n\nAssumptions and limitations: I assume the count of 80 well users is accurate; if some listed campers actually drank bottled water, the true attack rate is higher. Onset dates were partly self-reported, so the curve's start could shift by a day. The positive sample shows the parasite was present in the water, but it does not prove every case drank from that well, so matching individual cases to well use would strengthen the claim.
This model shows the level of evidence and organization needed to complete: Parallel worked CER (different scenario) modeling the outbreak source-and-agent format: a claim naming a likely source and agent, three independent evidence sources (curve, map, test), a quantitative measure, reasoning that ties the tools together, and stated limitations.
- Write one defensible claim.
- Choose specific evidence that supports the claim.
- Explain the scientific rule that connects the evidence to the claim.
Keep the structure. Replace the question, facts, measurements, and evidence. Then recheck units, vocabulary, and whether the conclusion goes beyond the evidence.
Also due today: Submit your CER on the class site, or hand it to Mr. Mendoza in class before the end of the period.
Claim ceiling: Today's evidence supports a classroom claim about today's lesson. It cannot prove causation, diagnose a real patient, or justify action outside this room.
One exam-style question that uses exactly what you practiced today. Try it before you reveal the answer, then read why each choice is right or wrong.
Tap an answer to see the full explanation. Nothing is recorded or graded.
It builds this reusable test skill: Calculating an attack rate from case and exposure data.
- Name the concept or data pattern being tested.
- Cross out choices that violate that rule or the evidence.
- Justify the best remaining choice before checking the answer.