Outbreak Investigation
Learning Objectives
Students will be able to:
- Apply epidemiological thinking to analyze outbreak scenarios
- Use data to identify likely transmission sources and routes
- Calculate attack rates to compare exposures
- Propose evidence-based explanations for outbreak patterns
You Are Disease Detectives!
The health department has received reports of 27 people sick with flu-like symptoms from Roosevelt Middle School. Your mission: Figure out what happened, where people got infected, and what should be done.
Investigation Framework: Person, Place, Time
Person
- Who got sick?
- What do they have in common?
- Age, activities?
Place
- Where were they?
- What locations overlap?
- Indoor vs. outdoor?
Time
- When did symptoms start?
- Work backward: exposure date
- Incubation period: 1-3 days
The Evidence
Outbreak Summary
- Cases: 23 students, 4 adults (27 total)
- Symptoms: Fever, cough, sore throat, body aches
- First cases reported: Wednesday, October 15
- Peak cases: Friday-Saturday, October 17-18
School Calendar
- Saturday, Oct 11: Fall Choir Concert, 7pm, School Auditorium
- Sunday, Oct 12: No school activities
- Monday, Oct 13: Regular classes, Choir practice 3-5pm
- Tuesday, Oct 14: Regular classes
Witness Statements
- "The choir concert was packed. Standing room only. It was really stuffy in there." — Parent
- "Our choir practice Monday was intense. We sang for 2 hours straight." — Student
- "The auditorium doors were kept closed due to cold, rainy weather." — Staff
Attack Rate Calculation
Attack rate = (Number sick / Number exposed) × 100%
| Group | Total People | Got Sick | Attack Rate |
|---|---|---|---|
| Choir members | 35 | 18 | 51% |
| Concert audience | 350 | 8 | 2.3% |
| Soccer team | 25 | 2 | 8% |
Key finding: Choir members had a MUCH higher attack rate than the audience. Why?
Solve the Mystery
Investigation Questions:
- What was the likely source event?
Hint: Work backward from symptoms (Wed-Fri) using 1-3 day incubation
- What type of transmission occurred?
Hint: Why did choir members get infected more than audience?
- What made this event high-risk?
Hint: Think about the 5 risk factors from Lesson 2
- What recommendations would you make?
Hint: How can future events be safer?
Solution Analysis
Click to reveal the analysis
Source Event: Fall Choir Concert, Saturday October 11
Why this setting was high-risk:
- Singing produces 10-50× more aerosol particles than talking
- 2-hour performance = extended exposure time
- Stuffy auditorium = poor ventilation
- Closed doors (due to weather) = no fresh air
- Packed audience = many potential susceptibles
Why choir higher than audience:
- Choir was actively singing (more particle production)
- Choir was on stage, closer together
- Choir had additional exposure at Monday practice
Transmission route: Aerosol (airborne)
Recommendations: Better ventilation at future events, open doors/windows when possible, don't perform when sick, consider portable air cleaners
Key Takeaway
Outbreak investigation uses Person, Place, and Time data to identify sources and transmission routes. Attack rates help compare which groups were most affected. In this case, the high attack rate among choir members (who were singing) compared to audience members (just sitting) points clearly to aerosol transmission as the main route—exactly what we'd expect from our earlier lessons!