In a waterborne outbreak, what epidemiologic pattern is often observed and what control measures are appropriate?

• A. A seasonal pattern with gradual increases
• B. A common-source pattern with a sharp rise and fall; controls include ensuring safe water supply, boil-water advisories, system disinfection, and public advisories
• C. A propagated outbreak spreading through contact
• D. A chronic disease pattern with steady incidence

Answer: (B)

Waterborne outbreaks are typically driven by a single contamination event, producing a common-source pattern: cases rise quickly after exposure to the contaminated water and then fall as the source is identified and exposure ceases. This reflects an acute, point-source exposure rather than ongoing person-to-person spread. The appropriate controls focus on removing or neutralizing the exposure and preventing further ingestion of contaminated water: ensuring a safe water supply, issuing boil-water advisories to inactivate pathogens, disinfecting the distribution system, and providing public advisories to inform people and reduce exposure. This approach aligns with the rapid rise-and-fall dynamic of a common-source outbreak, unlike the seasonal gradual increases, propagated outbreaks, or chronic steady incidence seen in other patterns.