Identify A Causative Agent
Use infection evidence to identify a causative agent step by step.
- Transmission basics: Outbreak work depends on agent, host, route, time, and place.
- Case definition: Students need a rule for who counts as a case before counting cases.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
Use infection evidence to identify a causative agent step by step.
| Evidence | Result |
|---|---|
| Symptoms | vomiting + cramps |
| Timing | 6 hours after meal |
| Lab | bacteria found in food |
| Control | unopened food negative |
Use the infection figure/table. Which evidence best supports a shared-source outbreak?
Reviewed| Evidence | Result |
|---|---|
| Symptoms | vomiting + cramps |
| Timing | 6 hours after meal |
| Lab | bacteria found in food |
| Control | unopened food negative |
- A.Cases with onset dates spread evenly over six weeks
- B.One person is much sicker than the others, with no exposure recorded
- C.A large total case count, even when the exposures are all different
- D.Several cases share the same exposure and close onset times
Show the worked solution ▾
Answer: D. Several cases share the same exposure and close onset times
- Step 1: Find shared exposure: A shared source means cases have a common exposure.
- Step 2: Check timing: Close onset times strengthen the pattern.
Why it's right: Shared exposure plus close timing supports a shared-source outbreak.
- A: Onsets spread evenly over weeks fit person-to-person spread, not one source.
- B: How sick one person is does not show that other people shared a source.
- C: A big count with different exposures points to many sources, not one.
Aligned to Biotechnology Research and Experiments · reading level ~grade 9
Under the microscope, cells from a patient sample are rod shaped and lined up end to end in chains. Using the three basic bacterial shapes, what is the shape called?
Reviewed- A.Chain, a shape all its own
- B.Spirillum, the spiral shape
- C.Coccus, the sphere shape
- D.Bacillus, the rod shape
Show the worked solution ▾
Answer: D. Bacillus, the rod shape
- Step 1: Read the shape of one cell: Each single cell is a rod.
- Step 2: Match the name: The rod shape is called a bacillus. How the rods line up is arrangement, not shape.
Why it's right: The three basic shapes are coccus for a sphere, bacillus for a rod, and spirillum for a spiral. These cells are rods, so they are bacilli.
- A: A chain describes how the cells are arranged, not the shape of one cell.
- B: A spirillum is spiral and never forms chains.
- C: A coccus is round. These cells are rods.
Aligned to Biotechnology Research and Experiments · reading level ~grade 9
- In Unit 3.1 Outbreak Evidence, this skill turns class evidence into a result another person can check.
Fill these in as you work through the lesson.
- Pathogen (disease-causing agent):
- Transmission (how a pathogen spreads):
- Reservoir (where pathogen lives):
- Case (person who fits outbreak definition):
Track the , route of transmission, time pattern, and exposed before making an outbreak claim.
- Who fits the case definition?
- What exposure do cases share?
- What timing pattern appears?
Use the infection diagram or line list to practice identify a causative agent.