Medical Detectives · Case File No. 003

The Fossil
Dig

A science-club dig. A cough that will not quit. Six suspects. Only one of them did it.

Case type: Disease Agents + Diagnosis · Difficulty: Detective, 3rd grade · You will need: the Case 3 Worksheet and everything from Activities 1.1 to 1.4.

The scene

Day 23.
Still coughing.

Marisol, age 12, loves fossils. Twenty-three days ago she spent a hot, windy Saturday at a science-club fossil dig. Ten days later the cough started. Then a fever. Then she woke up soaked in sweat. Then strange red bumps showed up on her shins.

Urgent care gave her an antibiotic. She took every dose. She got worse. Her parents brought her, and her medical file, to you.

Marisol is fictional. Her clues are real science. Your job: eliminate five suspects with evidence and name the one that did it.

The lineup

Six suspects. One did it.

Cartoon influenza virus
Suspect 1
Influenza virus
causes the flu
Virus
Cartoon measles virus
Suspect 2
Measles virus
causes measles
Virus
Cartoon pneumonia bacteria
Suspect 3
Streptococcus pneumoniae
causes pneumococcal pneumonia
Bacterium
Cartoon strep bacteria
Suspect 4
Group A Streptococcus
causes strep throat and scarlet fever
Bacterium
Cartoon ringworm fungus
Suspect 5
Trichophyton
causes ringworm
Fungus
Cartoon soil fungus
Suspect 6
Coccidioides
causes Valley fever
Fungus

Two viruses, two bacteria, two fungi. Their full files come after the evidence. Do not pick yet. A detective reads every clue before naming anyone.

Procedure

How to crack
the case

  • Read all six pieces of evidence: vitals, interview, exam, who got sick, labs, records.
  • Read the six suspect files.
  • Fill the elimination table on the Case 3 Worksheet: symptoms, timing, spread, labs.
  • Every ✗ needs a reason from the evidence.
  • The suspect still standing is your answer. Prove it with claim, evidence, reasoning.

Detective rule: a suspect is guilty only when every clue fits. The elimination board stays locked until all nine pieces of evidence are logged.

Evidence 1 · the vital signs · Activity 1.1

Read her vital signs

PatientMarisol T. (girl)
Age12
VisitDay 23
Height60 in.
Weight86 lb
Weight in August89 lb
TAP EACH VITAL SIGN · normal for a 12-year-old?

Think: three numbers are off. Which body system do they point to? And why would a girl lose 3 pounds in a month?

Evidence 2 · the interview · 23 days in order

What happened, day by day

Day 0 · SaturdayScience-club fossil dig in dry hills. Hot, dry, and windy. Marisol dug in the main pit for 4 hours. "Dust was everywhere. I was coughing up dirt."
Day 9The family adopts a kitten named Pepper. Marisol and her brother Leo hold her every day.
Day 10First symptom: very tired all day. A dry cough starts, slowly.
Day 12Fever and a headache.
Day 13Urgent care says, "Maybe a bacterial chest infection." She starts a 10-day antibiotic.
Day 17Wakes up soaked in sweat at night. Her chest hurts on deep breaths. Knees and ankles ache.
Day 21Tender red bumps appear on the front of both shins.
Day 23 · todayThe antibiotic ran out yesterday. She is not better. She is worse.

Also in the notes: no travel except the dig · no one at home is sick, not even Leo, who shares her bedroom · nobody in her class is sick except two other science-club kids.

Evidence 3 · the physical exam

What the doctor found

  • Eyes: normal. Not red, not watery.
  • Nose and throat: no runny nose. Tonsils normal, with no white spots. Nothing inside the cheeks.
  • Lungs: crackling sounds low on the right side. Breathing fast.
  • Skin: tender, raised, red-purple bumps on the front of both shins, each about the size of a quarter. They are not itchy, not scaly, and not ring-shaped. No rash on her face, chest, or scalp.
  • Joints: knees and ankles are sore but not swollen.

Detective rule: write down what is there AND what is not there. A missing symptom can clear a suspect.

Evidence 4 · who got sick? · think like Activity 1.2

Who else got sick?

The science-club advisor kept a sign-in sheet. Here is where everyone worked on Day 0, and who is sick now.

GroupWhere they were on Day 0PeopleSick now
Pit crew, no maskDigging in the main pit, in the wind and dust33
Pit crew, dust maskSam dug in the same pit but wore a dust mask all day10
Sifting crewScreening dirt under the shade tent, upwind of the pit60
AdultsThe bus and the snack table20
Families of the 3 sick kidsAt home with them: same houses, same bedrooms90

Lunch: all 12 people at the dig ate the same sandwiches and drank bottled water. Think: which group is like a control? What do the sick kids share that nobody else does?

Evidence 5 · the lab · read each result against its controls (Activity 1.4)

The lab results

Rapid flu test nose swab
Positive control
Negative control
Marisol

Which control does her sample match?

Rapid strep test throat swab
Positive control
Negative control
Marisol

Which control does her sample match?

Sputum culture on agar after 48 hours · Activity 1.3
Positive control
known bacteria
Negative control
nothing added
Marisol's sputum

Which plate does hers look like?

Evidence 6 · treatment so far and her records

Medicine, vaccines, and a kitten

The antibiotic

Amoxicillin, an antibiotic, for 10 days (Day 13 to Day 22). Mom checked off every dose:

Result: no better. Worse.

Immunization record

MMR vaccine (measles, mumps, rubella) · dose 1age 1 ✓
MMR vaccine · dose 2age 4 ✓
Flu shotnot yet this year

Two MMR doses protect about 97 of every 100 people from measles.

Pepper the kitten

Adopted on Day 9. The vet checked her: healthy, no bald or scaly patches. Leo holds Pepper every day, and Leo has no rash.

Activity 1.3 question: what kind of agent does an antibiotic kill? So what does it mean that 10 days of one did nothing?

Suspect files · 1 and 2 · viruses

The two viruses

Suspect 1 · virus

Influenza virus

The flu
Incubation
1 to 4 days
Symptoms
Starts suddenly. Fever or chills, cough, sore throat, runny or stuffy nose, muscle aches, headache, tiredness.
Spread
Person to person: droplets from coughs and sneezes, shared drinks, surfaces.
Treatment
Rest and fluids. An antiviral if caught early.
Suspect 2 · virus

Measles virus

Measles
Incubation
10 to 14 days
Symptoms
High fever, cough, runny nose, red, watery eyes, tiny white spots inside the mouth, then a flat red rash that starts on the face and spreads down to the feet.
Spread
Person to person. Extremely contagious: it can hang in the air of a room for 2 hours.
Treatment
Rest, fluids, fever control. Prevented by the MMR vaccine.
Suspect files · 3 and 4 · bacteria

The two bacteria

Suspect 3 · bacterium

Streptococcus pneumoniae

Pneumococcal pneumonia
Incubation
1 to 3 days
Symptoms
Fever, chills, cough, fast or hard breathing, chest pain, weakness, tiredness.
Spread
Person to person: droplets from an infected person's coughs and sneezes.
Treatment
Antibiotics.
Suspect 4 · bacterium

Group A Streptococcus

Strep throat and scarlet fever
Incubation
2 to 5 days
Symptoms
Throat pain, hard to swallow, red swollen tonsils with white spots, swollen neck glands, fever, headache, a red rash that feels like sandpaper.
Spread
Person to person: saliva, coughs, sneezes, shared food and drinks.
Treatment
Antibiotics.
Suspect files · 5 and 6 · fungi

The two fungi

Suspect 5 · fungus

Trichophyton

Ringworm
Incubation
4 to 14 days
Symptoms
Itchy, red, scaly, cracked skin in a ring-shaped rash. Sometimes blisters or patches of hair loss. It stays on the skin: no cough, no fever.
Spread
Touching an infected person or animal (cats, dogs), or shared towels and clothes.
Treatment
Antifungal cream.
Suspect 6 · fungus

Coccidioides

Valley fever
Incubation
1 to 3 weeks
Symptoms
Tiredness, cough, fever, chest pain, headache, night sweats, muscle or joint aches, a rash on the upper body or legs.
Spread
Lives in dry soil in parts of California and the Southwest. Digging or wind throws its spores into the air, and people breathe them in. Not spread from person to person.
Treatment
Rest. Antifungal medicine for serious cases.
Deduction · four questions for every suspect

The elimination board

Suspect 1 · Symptoms match?tired, dry cough, fever, night sweats, chest pain, aching joints, tender shin bumps; NO runny nose, red eyes, sore throat, or itch 2 · Timing fits?first symptom on Day 10; dig on Day 0; kitten on Day 9; no sick people near her 3 · Spread fits?only the unmasked pit crew got sick; nobody caught it from them 4 · Labs + treatment fit?flu and strep tests negative; no bacteria grew; antibiotic failed; 2 MMR doses ✔ total
Tap a suspect's name to see its file here.
✓ or ✗ in every box, then lock in:
Crack the case · a chain of three questions

Follow the chain

Link 1 · Bacteria or not?
Antibiotics kill bacteria. She took ten days of one and got worse. What did the agar plate show? Which two suspects does that clear?
Link 2 · A person or a place?
Leo shares her bedroom and is fine. The sifting crew is fine. If the agent jumped from person to person, who would have caught it? Which two suspects does that clear?
Link 3 · Two fungi left
Read the shin bumps in the exam word by word: tender, not itchy, not scaly, not a ring. And ringworm never makes you cough. Which fungus is left?
Bonus · the mask
Sam dug in the same pit as Marisol but wore a dust mask and stayed healthy. What does that tell you about how the agent got into her body?
Deliver your verdict

Name the
culprit

On the Case 3 Worksheet, finish the elimination table, follow the chain, and write your diagnosis.

  • "The agent is not a bacterium because ______."
  • "It did not spread from person to person. The clue that proves it is ______."
  • "Marisol has ______, caused by a fungus called ______."

Remember: exactly one suspect fits every clue. If two still fit, read the exam again.

Confirm it · after the worksheets are in

One blood test to be sure

A good detective confirms. The doctor orders one blood test for the agent the class named. Predict first: which control will Marisol's sample match?

Results for Valley fever blood test for Coccidioides
Positive control
Negative control
Marisol

POSITIVE. Her sample matches the positive control. Diagnosis confirmed.

1 · FluStarted slowly; no runny nose; no sick contact; flu test negative.
2 · MeaslesTiming fits, but no red eyes or mouth spots, wrong rash, nobody caught it, 2 MMR doses.
3 · PneumoniaSymptoms fit, but no sick contact, no bacteria grew, antibiotic failed.
4 · StrepNo sore throat, no sandpaper rash, strep test negative, antibiotic failed.
5 · RingwormThe decoy: a fungus and a new kitten, but no itch, no ring, and it never causes a cough.
6 · Valley feverEvery clue fits: the dusty dig, 10 days, only the unmasked diggers, a fungus.
Closing the case

Case
closed

🔒 Run the final test on the previous slide first.

Marisol has Valley fever. A fungus called Coccidioides lives in dry soil. Digging on a windy day threw its spores into the air, and she breathed them in. It never spreads from person to person, which is why Leo is fine.

Good news: most people get better with rest. Her doctor will watch her lungs and may give an antifungal medicine. The antibiotic never had a chance. Antibiotics only kill bacteria.

Protect yourself: wear a dust mask when digging in dry dirt, wet the soil first, and stay inside during dust storms.

Word Bank · Banco de Palabras

Tap a word for the full card.

Case 3 — Slide Index

— SLIDE 01/18