Who built upon John Snow's work?

• A. Ignaz Semmelweis and Koch
• B. Edward Jenner and Benjamin Jetsy
• C. John Snow
• D. Louis Pasteur

Answer: (A)

This question tests how later scientists expanded from Snow’s demonstration that diseases can be transmitted and traced in populations to more detailed understandings of infection and causation. Semmelweis showed that handwashing dramatically reduced puerperal fever, linking medical practices to the transmission of infection and showing that prevention can cut mortality. Robert Koch built on the germ-theory idea to identify specific pathogens and prove causation, developing methods to isolate microbes and establishing criteria (Koch’s postulates) for linking a microbe to a disease. Together, their work extends Snow’s epidemiologic focus on transmission into a microbiological framework that identifies causes and prevents outbreaks, making this pairing the best fit.

Edward Jenner’s vaccine work and the misspelled Jetsey aren’t direct continuations of Snow’s transmission-focused findings, while Pasteur certainly advanced germ theory, the combination with Semmelweis most directly reflects expanding Snow’s epidemiologic approach into identifying specific pathogens and infection control.