Source and agent CER
This page has four parts, in the order you use them. Part 1 is what you need to know. Part 2 says what to do, in plain English. Part 3 shows the work done once on a case that is not yours. Part 4 is your own work and where to turn it in.
Open your materials, follow the steps, then turn in your work.
Students write a CER identifying the likely source and infectious agent of the outbreak.
Check you have the right sheet: the top of it prints today's portal day, Source and agent CER. The PLTW activity itself is in myPLTW and is not posted here.
Optional: listen or watch a unit review▸
Part 1 of 4 · Background and definitions▸
💡 Big idea: A curve, a map, and an agent-ID test each measure something the others cannot, so an outbreak claim is trustworthy only because three independent lines of evidence agree on the same source.
- • Attack rate = (number of cases / number exposed) x 100: a quantitative measure of outbreak severity.
- • Multi-tool evidence means citing the curve, the map, and the test result independently, not as a single statement.
- • Assumptions reveal where the investigation could be wrong; limitations reveal where the data is incomplete.
Each identification test reads only one property of a , so narrowing to the true agent works by stacking several test results together to eliminate suspects, not by finding one test that names it.
A curve, a map, and an agent-ID test each measure something the others cannot, so an outbreak claim is trustworthy only because three independent lines of evidence agree on the same source.
Driving question: Can you write a claim naming the outbreak's source and agent that survives scrutiny because the curve, the map, and the test result each point to it on their own?
What you already know: Each identification test reads only one property of a , so narrowing to the true agent works by stacking several test results together to eliminate suspects, not by finding one test that names it.
New idea: A curve, a map, and an agent-ID test each measure something the others cannot, so an outbreak claim is trustworthy only because three independent lines of evidence agree on the same source.
- Observe or measure the relevant feature in today's lesson.
- Organize the observation with a stable evidence ID.
- Apply this rule: Patterns across time and connection can narrow a explanation without proving it by themselves.
- Choose the option the evidence supports and state the limit of the conclusion.
Real biomedical example: Can you write a claim naming the outbreak's source and agent that survives scrutiny because the curve, the map, and the test result each point to it on their own?
What the evidence supports: E1 to E3 and the figure support the daily take-home when the response meets the stated success criteria.
What it cannot prove: The package does not support claims beyond this lesson's or any real patient diagnosis.
- • epidemiology: The study of how diseases spread, who they affect, and what causes them across populations, used to find patterns and guide prevention.
- • : A table used in outbreak investigations where each row records one patient's key details, such as symptoms, dates, and exposures.
- • : A bar graph showing the number of new disease cases over time, used to track how fast an outbreak is growing or shrinking.
- • : Keeping samples or cultures at a controlled warm temperature for a set time so cells, microbes, or reactions can grow or proceed.
- • prevalence: The share of a population that has a particular disease or condition at a given time, often shown as a percentage.
- • incidence: The number of new cases of a disease that appear in a population during a set period of time.
- • : The specific organism or factor, such as a bacterium, virus, or , that directly produces a particular disease.
Use it now: Choose one decision option. Cite E1 and E3, then explain how the rule connects the evidence to your choice. This is thinking practice for the one turn-in named under Turn in, not a second submission.
Go further, optional: The source links below are optional enrichment. Every fact required for today's local evidence decision appears in this lesson package.
Patterns across person, place, and time can narrow an outbreak hypothesis, but they require case definitions, comparison data, and laboratory or epidemiological confirmation before a source is established.
Limit: A classroom map or curve can support a limited hypothesis and next investigation step, not a confirmed source or individual diagnosis.
Patterns across time and connection can narrow a explanation without proving it by themselves.
Limit: People change behavior, infections have periods, and surveillance data can be incomplete.
Write a CER naming source and agent with multi-tool evidence.
Limit: E3 defines the classroom product or success criterion. It is not independent scientific evidence and cannot justify a clinical or causal claim.
Today's decision · Simulated classroom evidence scenario
Your role: biomedical investigator
Decision: Your team must decide what the evidence from today's lesson supports before submitting the claim-evidence-reasoning response named on today's page.
- • Support the claim by saying the curve, the map, and the test all show the same dish caused it.
- • Gather comparison data on who ate the suspected dish and who did not, because case counts alone cannot show what differed.
- • Name the source only when the curve's timing, the map's location, and the test's biology each point there independently.
Response: State one choice, cite at least two evidence IDs, explain the rule that connects them, and add one limitation. Use it inside the one turn-in named under Turn in; it is not a separate submission.
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.
Reason for review: Your team must decide what the evidence from today's lesson supports before submitting the claim-evidence-reasoning response named on today's page.
Context: A strong outbreak claim earns trust by triangulation: the same source is pointed to independently by the timing (curve), the geography (map), and the biology (agent ID), and a claim standing on only one of these is weak no matter how confident it sounds.
- • T1: State a claim naming the likely source and agent of the outbreak.
- • T2: Cite epidemic-curve, map, and identification-test evidence.
- • T3: Explain reasoning that links exposure patterns to the proposed source.
- • T4: Quantify the outbreak using incidence and attack-rate values.
- • T5: Identify assumptions and limitations in the data and methods.
- • E1: Patterns across person, place, and time can narrow an outbreak hypothesis, but they require case definitions, comparison data, and laboratory or epidemiological confirmation before a source is established.
- • E2: Patterns across time and connection can narrow a explanation without proving it by themselves.
- • E3: Write a CER naming source and agent with multi-tool evidence.
Measurements: Use only the measurements, units, graph, or counts supplied in today's task. No additional patient measurement is implied.
Figure finding: Three boxes labeled curve when, map where and test what, with arrows converging on an empty dashed source-and-agent box, and the attack-rate formula written beneath.
Uncertainty: This is a composite classroom scenario. Missing history, measurements, or confirmation tests remain unknown and limit the conclusion.
Students often think citing evidence means restating their conclusion a few times in different words, so 'the curve, map, and test all show it was the same dish' reads to them like three pieces of evidence. The trap: That is one claim stated three times, not three pieces of evidence, because real triangulation means each source contributes something the others cannot (the curve gives timing, the map gives location, the test gives biology), and only when three independent lines agree does the claim actually get stronger.
- CER:
- Claim, Evidence, Reasoning: make a claim, back it with evidence, explain your reasoning.
- SOP:
- Standard Operating Procedure, the exact steps to follow (especially in a lab).
- Tracker:
- Your PLTW progress log where you record completed evidence.
- myPLTW:
- The PLTW course site where you do the online activities. Find it in Clever with your Microsoft sign-in, right next to Schoology.
Tap the speaker to hear a term. Add two of these to your notebook glossary with a definition and an example in your own words.
Pick just 2 or 3 words from today and make them yours: write what each one means in your own words, name the context clue or evidence that helped, then give one example from what you actually did in Source and agent CER. Try your own words first; the glossary is there if you get stuck. This is voluntary and counts as extra credit, so keep it short.
Saved on this device. Show Mr. Mendoza or add these to your notebook glossary to claim the extra credit.
Part 2 of 4 · Directions in plain English▸
2.1 Open your materials
Practice outbreak dataset (made-up practice data, not the class outbreak and not real patients)
The setting
- A practice hospital watched three units for 12 days, Day 1 to Day 12. A case is a patient with a new wound infection or fever that started on one of those days.
- Use this dataset only if you do not have your class line list, curve, map and agent-ID results. Write "practice dataset" on anything you build from it.
Line list: one row per case
| Case | Unit and room | Onset day | Main sign | Dressing change from the 3 North supply cart? | Gram stain | Colony: color, form, elevation, margin | Oxidase test |
|---|---|---|---|---|---|---|---|
| 1 | 4 East, room 412 | Day 2 | Red, painful wound | No | Positive, rods | Tan, circular, raised, entire | Negative |
| 2 | 3 North, room 306 | Day 3 | Wound drainage and fever | Yes | Negative, rods | Cream with a green tint, irregular, flat, undulate | Positive |
| 3 | 3 North, room 312 | Day 4 | Wound drainage | Yes | Negative, rods | Cream with a green tint, irregular, flat, undulate | Positive |
| 4 | 3 North, room 308 | Day 4 | Fever | Yes | Negative, rods | Cream with a green tint, irregular, flat, undulate | Positive |
| 5 | 3 North, room 314 | Day 5 | Wound drainage | Yes | Negative, rods | Cream with a green tint, irregular, flat, undulate | Positive |
| 6 | 3 North, room 303 | Day 5 | Wound drainage and fever | Yes | Negative, rods | Cream with a green tint, irregular, flat, undulate | Positive |
| 7 | 3 North, room 310 | Day 5 | Fever | Yes | Negative, rods | Cream with a green tint, irregular, flat, undulate | Positive |
| 8 | 3 North, room 316 | Day 6 | Wound drainage | Yes | Negative, rods | Cream with a green tint, irregular, flat, undulate | Positive |
| 9 | 3 North, room 311 | Day 6 | Wound drainage and fever | Yes | Negative, rods | Cream with a green tint, irregular, flat, undulate | Positive |
| 10 | 3 North, room 318 | Day 7 | Fever | No | Negative, rods | Cream with a green tint, irregular, flat, undulate | Positive |
| 11 | 3 North, room 305 | Day 8 | Wound drainage | Yes | Negative, rods | Cream with a green tint, irregular, flat, undulate | Positive |
| 12 | 3 South, room 327 | Day 10 | Fever | No | Negative, rods | Cream, circular, convex, entire | Negative |
Patients at risk, Day 1 to Day 12
| Unit | Patients on the unit during Day 1 to Day 12 | Of those, patients who had a dressing change from the 3 North supply cart |
|---|---|---|
| 3 North | 40 | 20 |
| 3 South | 50 | 0 |
| 4 East | 30 | 0 |
Map key for the spot map
- Each unit is one hallway. 3 North is rooms 301 to 320, odd numbers on the left side and even numbers on the right. The 3 North supply room, where the dressing cart is kept, sits between rooms 309 and 311.
- 3 South is rooms 321 to 340 on the same floor, across the elevator lobby from 3 North. 4 East is rooms 401 to 420, one floor up.
Practice candidate key (made-up candidates, not the class culture key)
| Candidate | Gram stain | Colony color | Oxidase test |
|---|---|---|---|
| Candidate A | Positive, rods | Tan | Negative |
| Candidate B | Positive, cocci in chains | White or gray, small | Negative |
| Candidate C | Negative, rods | Cream | Negative |
| Candidate D | Negative, rods | Cream with a green tint | Positive |
- Cross a candidate off as soon as one result does not fit it. A match narrows the field; it does not confirm an identity.
The two rates you calculate
- Incidence: new cases during Day 1 to Day 12, divided by the patients at risk during Day 1 to Day 12, times 100. Say which group you used: the whole hospital or one unit.
- Attack rate: cases among the patients who had the exposure, divided by all patients who had that exposure, times 100. Compare it with the same rate for patients on the unit who did not have the exposure.
2.2 Start the work
State a claim naming the likely source and agent of the outbreak.
Show all 5 required steps
- State a claim naming the likely source and agent of the outbreak.
- Cite epidemic-curve, map, and identification-test evidence.
- Explain reasoning that links exposure patterns to the proposed source.
- Quantify the outbreak using incidence and attack-rate values.
- Identify assumptions and limitations in the data and methods.
Lost your place? You are writing a CER. Check your progress: claim naming source and agent (1), cited curve, map, and test evidence separately (2), reasoning that links exposure pattern to source (3), incidence and attack-rate numbers (4), assumptions and limitations (5). Resume at your first missing piece.
- 0-8 minReview the lab data: confirm curve shape, map cluster location, and agent-ID result.
- 8-20 minWrite the claim: name the likely source (location/event) and infectious agent in one sentence.
- 20-45 minWrite evidence: cite curve shape, map cluster, and agent-ID result as three separate points.
- 45-60 minWrite reasoning: connect exposure patterns to the proposed source for each evidence point.
- 60-70 minCalculate and insert the incidence and the attack rate, each with its numerator, denominator and time period; add assumptions and limitations.
- 70-80 min: confirm three evidence sources are cited, incidence and attack rate are both present, limitation stated.
- • The you Gram stain today comes from the plates Mr. Mendoza streaked in advance; they incubated at 30 degrees C for 48 hours before you read them on the day. If your class opens plates and Gram stains today (the 3.1.6 sheet), comes first, and the sheet's rule is absolute: all the flame work happens first, in one go, with the ethanol still in the cupboard. Then every lamp in the room is out and confirmed out loud before anything flammable is opened. Goggles and a lab coat on, plates open only at the bench, slides and plates into the biohazard container.
- • You have the curve, the map, and the agent-ID results from the lab: today you build the argument.
- • Every piece of evidence must be cited by the tool that produced it, not just described generically.
- • The quantitative section is mandatory: an incidence value and an attack rate turn a description into a measure.
- • Your limitation should point to one specific gap in the lab data that could change your conclusion.
PLTW connection and today's work
In myPLTW, open Lesson 3.1 Nosocomial Nightmare and go to Activity 3.1.6 Gram Staining. Use it as the scaffold for your source-identification CER.
Today's stopping point: Platform prompts done in first 15 minutes; full CER submitted before end of period.
PLTW activity titles identify the course connection. If your account will not open, use the posted materials for today and tell Mr. Mendoza. Do not mark an online activity complete unless you completed it.
Use the turn-in directions in Part 4 of this page. Do not create a second submission unless your teacher asks for one.
Show another explanation or a smaller first step
Need help? Choose a starting point
Finish the assigned lab safely before starting extra practice.
Part 3 of 4 · Worked example▸
This is a parallel case, not your own. Read it for the order of the work, then do your own in Part 4.
This is a MODEL from a different case, not the answer to today's outbreak. Study how the pieces fit together, then build your own argument from your own curve, map, and test.
Scenario (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.
Claim: 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).
Evidence (three independent sources):
- Epidemic curve: cases rose gradually and stayed elevated for about a week, a continuous-source pattern rather than one sharp peak.
- Spot map: cases were spread across cabins on the well-fed side of camp, not clustered around any single meal or event.
- Agent ID: a water sample from the well tested positive for Giardia cysts, a parasite spread through contaminated water.
Quantitative measure: Attack rate = (24 cases / 80 campers using the well) x 100 = 30 percent.
Reasoning: 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.
Assumptions 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 as one PDF in Schoology.
Wet footprints appear across connected rooms after one person enters from the rain.
- Which footprint came first?
- Which rooms connect?
- What pattern would support more than one entry point?
Patterns across time and connection can narrow a explanation without proving it by themselves.
People change behavior, infections have periods, and surveillance data can be incomplete.
- • Footprints map to recorded cases.
- • Room connections map to exposures.
- • The route hypothesis maps to a limited claim.
Part 4 of 4 · Your work▸
Check your work before submitting
- Write a CER naming source and agent with multi-tool evidence.
- Include a quantitative measure and at least one limitation.
Before lab work: read the safety rules
- The colony you Gram stain today comes from the plates Mr. Mendoza streaked in advance; they incubated at 30 degrees C for 48 hours before you read them on the isolation day. If your class opens plates and Gram stains today (the 3.1.6 sheet), safety comes first, and the sheet's rule is absolute: all the flame work happens first, in one go, with the ethanol still in the cupboard. Then every lamp in the room is out and confirmed out loud before anything flammable is opened. Goggles and a lab coat on, plates open only at the bench, slides and plates into the biohazard container.
- If the stain is a demonstration or the results are printed, there are no bench hazards today.
4.1 Turn in your work
DueCheck the Schoology assignment for this day- Hand in
- CER naming the likely outbreak source and infectious agent, citing epidemic curve, spot map, and agent-ID evidence, including both an incidence value and an attack rate, and stating assumptions and limitations.
How to submit and name your file
Submit as one PDF in Schoology.
In Schoology, open your course and the assignment for this lesson. Attach your file, select Submit, and check that it appears in the submission.
PDF upload helpYou get two school days for every day you were absent, so this deadline moves with you.
Today's lesson is in Schoology
Each school day has one lesson page in Schoology that holds everything for the day: the goal, the story so far, every table and data value, the numbered steps, and what to turn in. Open it first and work from it. The other rows for this day, if any, are the score line for a paper quiz or test and the John Carroll debate item; they do not add work. Check Schoology for each deadline.
- Today's Lesson · Mon 11/30 · Wk15 · Narrow down the agent, then trace the chain of infection(today's lesson page: the goal, the data, the steps, and what to turn in are all on it)
Link will not open? Open Schoology, choose your course and section, and find the title shown above.
- CompleteEvery required part of the artifact is present, nothing left blank.
- AccurateThe science and the data are correct and match the evidence.
- Scientific reasoningYou explain your claim with evidence and reasoning (CER), not just an answer.
- Professional communicationClear, organized, labeled, and written the way a clinician or scientist would.
- SubmittedGo to Schoology to turn this in. Submit one PDF. Schoology attaches your name to your upload; on the page itself, write your period and code. Name the file: FirstName LastName - Assignment Title - YYYY-MM-DD.pdf. If you cannot get in, see Mr. Mendoza. Do not skip the work.
- Error analysis and method · counts doubleName a specific limit of the method and how it moved your result, and compare what you predicted to what happened. "Human error" does not count; say what about the procedure or instrument caused it.
How this lesson connects
Keep using what you learned last class: Each identification test reads only one property of a pathogen, so narrowing to the true agent works by stacking several test results together to eliminate suspects, not by finding one test that names it. Today: A curve, a map, and an agent-ID test each measure something the others cannot, so an outbreak claim is trustworthy only because three independent lines of evidence agree on the same source.
Practice: try a question, then check your answer▸
Claim ceiling for this check: 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.
A student writes: 'The source was dish A. Evidence: the curve shows dish A, the map shows dish A, the test shows dish A.' What is wrong with this as multi-tool evidence, and how should each line actually read?
Write an answer and pick a confidence to unlock the key.
Fast retrieval with instant answers, not the commit-then-reveal check above. Try each from memory first: write what you remember about the earlier units, then check yourself here.
Missed class or ready for more?▸
Run this before you touch the bench. It is built from the real lab procedure, so the decisions you make here are the ones you will make with the equipment in your hands.
I can name the procedure's purpose and the evidence I will record. I can name today's hazards and the control for each: The colony you Gram stain today comes from the plates Mr. Mendoza streaked in advance; they incubated at 30 degrees C for 48 hours before you read them on the isolation day. If your class opens plates and Gram stains today (the 3.1.6 sheet), safety comes first, and the sheet's rule is absolute: all the flame work happens first, in one go, with the ethanol still in the cupboard. Then every lamp in the room is out and confirmed out loud before anything flammable is opened. Goggles and a lab coat on, plates open only at the bench, slides and plates into the biohazard container. My data table is ready before materials are handled.
Finish the checklist before you handle any material.
- • The colony you Gram stain today comes from the plates Mr. Mendoza streaked in advance; they incubated at 30 degrees C for 48 hours before you read them on the isolation day. If your class opens plates and Gram stains today (the 3.1.6 sheet), safety comes first, and the sheet's rule is absolute: all the flame work happens first, in one go, with the ethanol still in the cupboard. Then every lamp in the room is out and confirmed out loud before anything flammable is opened. Goggles and a lab coat on, plates open only at the bench, slides and plates into the biohazard container.
- • If the stain is a demonstration or the results are printed, there are no bench hazards today.
- 1Before materials are handled, identify the purpose, variables or comparison, controls, measurement units, and stop-work condition.
- 2State a claim naming the likely source and agent of the outbreak.
- 3Cite epidemic-curve, map, and identification-test evidence.
- 4Explain reasoning that links exposure patterns to the proposed source.
- 5Quantify the outbreak using incidence and attack-rate values.
- 6Identify assumptions and limitations in the data and methods.
- 7Record each result in the prepared table before interpreting it. Mark missing, repeated, or invalid results truthfully.
- 8Complete the named cleanup and waste route, remove PPE safely, wash hands when required, and confirm the station is ready for the next group.
| Which trial or sample this row is | What you changed on purpose | What you measured, with units | What you saw, before you explain it | Anything that could make this reading wrong |
|---|---|---|---|---|
Before the procedure, predict the result and cite the rule behind the prediction.
After the procedure, compare the result with the prediction and name one limitation or source of uncertainty.
What today's skills lead to. These are real health-science careers this course builds toward. Tap one to see, on the US Department of Labor's O*NET site, what the job actually involves, what it pays, and how fast it is growing.
Missed the lab days, or do not have your curve, map and agent-ID results? Use the practice outbreak dataset in Part 2 of this page: plot the and spot map, narrow the candidates with the practice key, and calculate the incidence and the attack rate from its population table. Then write the same CER from that data, write "practice dataset" at the top, and submit it as one PDF in Schoology.
Submit as one PDF in Schoology.
Class still runs. Complete today's work as this page describes (it is self-guided). Need the concept taught without a teacher? Use this authoritative explainer:
CDC: principles of epidemiology and outbreak investigationThe optional extra-credit track is open. Complete reserved-unit work from home, including virtual labs, for extra credit. Each item shows its correct submission route.
Open the extra-credit trackSources: slides, readings, and resources▸
The deck carries the prior idea forward, lets you inspect an analogy, maps the rule to biology, and ends with the same evidence decision and exit ticket used on this page.
Play the cold open at the start of the unit to set the scene. Each recording is AI-generated and simulated (fictional callers, no real people or student data).
Hand-picked readings and interactives for this lesson, from authoritative open organizations and PLTW's own public course outline.
This week
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