According to John Snow, which statement is sometimes unnecessary to prevent disease?

• A. Pathogenic mechanism
• B. Water source identification
• C. Vaccination
• D. Public health surveillance

Answer: (A)

Focusing on how people are exposed and how transmission occurs can be enough to stop an outbreak, even without knowing the exact biology of the pathogen. John Snow showed this during the cholera outbreak by tracing cases to a contaminated water source and removing the Broad Street pump handle, which interrupted transmission and saved lives. The immediate preventive move was to cut off exposure, not to understand the precise pathogenic mechanism of cholera. This illustrates that practical control measures—like identifying and eliminating the source of infection or interrupting transmission—can work even when the detailed biology isn’t yet known. While pinpointing the water source matters, and surveillance helps detect outbreaks and vaccination can be helpful in prevention, the specific way the pathogen causes disease isn’t always necessary for effective prevention in an outbreak context.