Agent / host / environement triad = Chain of transmission
- Agent / Host / Environment = agent capable of causing disease and its source + host or persons susceptible to agent + environment allowing them to get together
- Infectious groups: viruses, bacteria, protistans (protozoa), fungi, animals (worms)
- Testable - hypothesis must be in a form that is testable
- Current knowledge and background - it should be based upon current knowledge and be updated or modified as new information is uncovered !!!