Which theory built upon John Snow's germ theory by introducing the idea that microorganisms cause disease?

• A. Theory of Multiple Causality
• B. Handwashing Theory
• C. Miasma Theory
• D. Koch Postulates Theory

Answer: (D)

Proving that a specific microorganism causes disease requires a rigorous framework to demonstrate causation, not just association. The Koch postulates provide that framework, building on germ theory by turning the idea that microbes can cause illness into a testable sequence of steps. The idea is that the suspected microbe must be found in every case of the disease, isolated and grown in pure culture, cause the disease when introduced into a healthy host, and then be re-isolated from that newly diseased host. This formal set of criteria gave scientists a clear method to prove causation rather than mere correlation, which is why it’s considered the concept that extends germ theory in this way. The other options don’t offer that explicit causal proving method: the miasma idea attributes illness to bad air with no microbial causation; the prevention-focused notions (like handwashing) address control rather than proving causation; and a broad multiple-causality idea doesn’t provide the specific steps for linking a microbe to a disease.