John Hay Biomedical · Medical Interventions · Outbreak research library
Research possible explanations
Question: How can we compare possible causes without calling a symptom match a diagnosis?
Use this library with your official PLTW Day 1 histories in Schoology. This is original support for Activity 1.1.2. It contains no official case facts or case answers.
Read the rule and Model R first. Then open the reference cards you need. You do not need an outside search. The source links let you check or extend the reading.
Read the rule
In Checkpoint A, you separated measured signs from reported symptoms. Those clues describe what happened. They may fit more than one explanation.
A hypothesis is an explanation we can test. An infectious agent is a biological cause of infection, such as a bacterium or virus. An illness name may describe a condition without naming its agent.
A diagnosis identifies a condition using the full clinical evidence. A short history may support possible explanations, but it usually cannot confirm one. This classroom work is not medical advice.
- Copy one relevant case clue and its source page.
- Compare it with a reference fact. Cite the card ID and source title.
- Name a missing or conflicting fact. A missing clue is not a negative test.
- Write what new record would help separate the possibilities.
Real example: CDC explains that flu and COVID-19 can share symptoms. Symptoms alone cannot reliably distinguish them. Laboratory testing may help separate those causes. See R2 and R3.
Our cards are a starting set, not every possible illness. Conditions can overlap. For example, influenza can lead to pneumonia. Do not assume each history has one unique answer.
Model R: practice before the case
Original simulated, AI-assisted practice. This is separate from PLTW. Record MR1: a fictional adult reports a runny nose and cough. Record MR2: symptoms began gradually. Record MR3: no laboratory result is supplied.
Worked comparison: A common cold is one possibility. R1 lists cough and a runny nose as possible clues. COVID-19 is another possibility because R2 also lists these clues. The records do not identify a virus.
Worked evidence note: MR1 fits both R1 and R2. MR3 leaves the cause untested. A clinician's assessment and an appropriate laboratory result could help distinguish causes. Gradual onset does not rule out every alternative.
Use it now: Does MR1 prove that two people with a cough share one infection? Explain in one sentence before checking below.
Check the practice answer
No. Similar symptoms can have different causes. A symptom match supports a possibility, not a shared infection or direction of spread.
What to notice: the sequence is source clue → reference fact → possible explanation → missing evidence. The same sequence works in a diagram or a written list.
Reference cards R1 to R8
Open cards that help compare your case clues. Record the ID, title, and source link in your notes. Never copy Model R into the official case record.
R1 · Common cold
Cause: several respiratory viruses can cause a cold. Rhinoviruses are common causes.
Possible clues: a runny or blocked nose, cough, sneezing, a sore throat, and mild aches. Symptoms often build gradually.
Limit: other infections can look similar. These clues do not identify a specific virus. Compare the timing and other findings; mark missing information as unknown.
Sources: CDC, About Common Cold (2026); CDC, Signs and Symptoms of Flu (2024, cold and flu comparison).
R2 · COVID-19
Cause: the SARS-CoV-2 virus.
Possible clues: fever, cough, fatigue, a sore throat, and nasal symptoms. Some people have a change in smell or taste. Symptoms vary.
Limit: symptoms alone cannot distinguish COVID-19 from flu. An appropriate laboratory test can help. A history with no test result does not establish either a positive or negative result.
Source: CDC, Symptoms of COVID-19 (2025).
R3 · Influenza, or flu
Cause: influenza viruses infect the respiratory system.
Possible clues: symptoms often start suddenly and may include cough, body aches, headache, and fatigue. Fever is common but is not always present.
Limit: several infections share these clues. Onset means when symptoms began. Compare onset and the whole history, then name the laboratory evidence that is still missing.
Source: CDC, Signs and Symptoms of Flu (2024).
R4 · Meningococcal disease
Cause: Neisseria meningitidis bacteria. They can cause infection around the brain and spinal cord, or in the bloodstream.
Possible clues: fever and headache may occur. Neck stiffness can occur with meningitis. Early illness can resemble flu and may worsen quickly.
Exposure: spread can involve close or lengthy contact with respiratory or throat secretions.
Limit: not every kind of meningitis has this cause. Missing symptoms do not rule it out. Clinical assessment and laboratory evidence are needed. This is a serious medical condition, not something to diagnose in class.
Sources: CDC, About Meningococcal Disease and Symptoms (2026).
R5 · Infectious mononucleosis, or mono
Cause: Epstein-Barr virus, or EBV, is the most common cause. Other infections can also cause mono.
Possible clues: marked fatigue, fever, a sore throat, and swollen lymph nodes. Lymph nodes are small structures involved in immune defense.
Exposure: EBV commonly spreads through saliva. Symptoms often begin several weeks after infection.
Limit: fatigue or shared drinks alone do not establish mono. Review the timeline and full clinical findings. A recent contact is not automatically the exposure that caused illness.
Source: CDC, About Infectious Mononucleosis (2024).
R6 · Pneumonia
Condition: pneumonia is an infection in the lungs. Bacteria and viruses are common causes; other agents can also cause it.
Possible clues: cough, fever, fatigue, shortness of breath, or chest pain with breathing or coughing.
Limit: pneumonia is not the name of one agent. Flu and COVID-19 can cause pneumonia. Cough and fever alone do not establish a lung infection. Clinical findings and tests would help evaluate it.
Source: CDC, About Pneumonia (2026).
R7 · Strep throat
Cause: group A Streptococcus bacteria.
Possible clues: a sore throat that starts quickly, painful swallowing, fever, and swollen neck lymph nodes. Close contact can increase exposure risk.
Limit: a sore throat has many possible causes. Cough or a runny nose points more toward a viral cause, but a clue alone is not a diagnosis. A clinician may use a throat test to check for group A strep.
Source: CDC, About Strep Throat (2026).
R8 · Sleep deficiency
Possible contributor: too little sleep, poor-quality sleep, or sleep at the wrong time can affect daytime function.
Possible clues: trouble staying alert, concentrating, or learning. Sleep deficiency itself is not an infectious agent.
Limit: this may contribute to fatigue without explaining all other findings. Do not use a sleep history to dismiss fever or exclude an infection. More than one factor may affect a person.
Source: NHLBI, Sleep Deprivation and Deficiency (2022).
Your research-note outline
Use this outline under each of your seven case notes. Short phrases are enough; you do not need a paragraph for every field. Compare two plausible possibilities when the sources support two. If they do not, name the missing evidence instead of forcing a second answer.
Then check your existing contact map. Correct unsupported connections. Keep each label tied to a Day 1 source fact. Do not circle a confirmed source of infection.
Below your map or connection list, write one testable explanation about a possible connection. Name a new record that could support or weaken it. This is the explanation you will discuss and revise at Checkpoint C.
I1 · Treatment and reducing spread
An intervention is an action intended to improve health. Treatment helps the ill person. Containment aims to reduce further spread.
Different causes call for different actions. Antibiotics treat certain bacterial infections. They do not treat viruses. Some viral infections have antiviral treatments. Clinicians choose care using the diagnosis and the person's needs.
Reducing spread also depends on the route of spread. For respiratory viruses, cleaner indoor air and hygiene can reduce exposure. Vaccination can help prevent illness. Public health teams guide disease-specific steps.
Use it: propose an action conditionally: “If evidence supports this cause, a health professional could consider __ because __.” Explain whether it treats illness or reduces spread. Do not prescribe a drug or dose.
Sources: MedlinePlus, Infectious Diseases (2024); CDC, Antibiotic Do's and Don'ts (2025); CDC, Preventing Respiratory Illnesses.
C1 · Contact tracing and privacy
Contact tracing helps public health teams find people who may have been exposed to an infection. Investigators ask about symptoms, when they began, places visited, and contacts.
A public health nurse may help people understand prevention and find health services. A classroom map is only practice; it is not an actual contact-tracing investigation.
Use it: name one missing time or contact detail in the fictional records. Explain how that detail could help an investigator. Use only the supplied fictional case. Do not share your family's or classmates' health information.
Source: CDC NERD Academy, Why is contact tracing so important? (2024). The video is optional; the information needed for our task is above.
Model R: explain and revise
For Checkpoint C, also read I1: treatment and reducing spread and C1: contact tracing and privacy.
Claim, evidence, reasoning (CER) is a way to explain a decision. The claim says what you think. Evidence gives source-backed facts. Reasoning explains why those facts support the claim.
Practice claim: a respiratory infection is a possible explanation for Model R, but its cause remains unknown.
Evidence and reasoning: MR1 reports cough and a runny nose. R1 and R2 show that these clues fit more than one infection. MR2 describes gradual onset, which can fit a cold. MR3 supplies no test result. Together, these facts support comparison and further evaluation, not a confirmed cause.
Revision: if a partner points out that symptoms overlap, replace “definitely a cold” with a tentative claim. A tentative claim is one you may change when more evidence arrives.
Your writing outline: My current explanation is __. The case record shows __ (page __). Reference __ says __. These facts matter because __. However, __ remains unknown. A new __ record could help by __.
Write one response about the tentative connection you wrote below your map or connection list at Checkpoint B. You do not need a separate response for every history. Use at least three evidence points from the official histories and your cited references together. Discuss what supports the explanation and what weakens it. Do not turn a possibility into a confirmed pathogen or source.
Next: official conclusions. Open Activity 1.1.2 in our Schoology materials hub. Answer all three conclusion questions on page 10 of its PDF. Use I1 where relevant.
Return to today's directions
For either checkpoint, submit the required parts together as one PDF. Include readable photos of any paper work. Keep an editable copy. The upload guide can help you check and submit your PDF.