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Difficulty: HardDisease Surveillance and Outbreak Management

A regional epidemiologist is reviewing initial surveillance reports from four distinct clusters of infectious diseases. To guide the investigation strategy, match each cluster description to its classic epidemiological curve pattern and primary transmission dynamic.

  • Dozens of attendees of a single-afternoon outdoor festival develop sudden-onset severe nausea and vomiting roughly 4 hours after the event.A curve with a single, sharp peak where all cases fall within one incubation period; indicates a point source outbreak.
  • A community observes an initial small cluster of bloody diarrhea and tenesmus, followed by a larger wave of identical cases in household contacts 2 to 3 days later.A curve with progressively taller peaks separated by roughly one incubation period; indicates a propagated outbreak.
  • A steady, uninterrupted stream of Legionnaires' disease cases is reported over two months in a hospital, halting only when the HVAC cooling towers are chemically decontaminated.A curve with a rapid ascent that plateaus and remains elevated until the exposure ends; indicates a continuous common source outbreak.
  • Cases of acute gastroenteritis repeatedly surge every 10 to 14 days among patrons of a specific recreational swimming lake, corresponding to heavy rainfall events.A curve with multiple irregular peaks not separated by a consistent incubation period; indicates an intermittent common source outbreak.

Answer

Festival attendees match to point source outbreak; household diarrhea clusters match to propagated outbreak; hospital Legionnaires' matches to continuous common source; lake gastroenteritis matches to intermittent common source.
Outbreaks are classified by their exposure source and transmission dynamics, which generate characteristic epidemic curves. Point source outbreaks stem from a single, brief exposure, causing a single sharp peak. Continuous common source outbreaks result from prolonged exposure, creating a plateau. Intermittent common source outbreaks arise from recurring discrete exposures, forming irregular peaks. Propagated outbreaks involve person-to-person spread, resulting in successively larger peaks separated by the disease's typical incubation period.

Step-by-Step Solution

1
Analyze the exposure duration for each cluster.
The festival is a brief, single exposure. The hospital cooling tower is a prolonged, constant exposure. The lake is a recurring but discontinuous exposure. The bloody diarrhea involves secondary spread.
Identifying the exposure duration and continuity distinguishes common source types.
2
Determine if secondary person-to-person transmission is occurring.
The household clusters of bloody diarrhea occur 2-3 days after initial cases, indicating secondary transmission.
Person-to-person spread defines a propagated outbreak rather than a common source outbreak.
3
Correlate findings to classic epidemiological curve shapes.
Brief exposures create a single peak (point source). Constant exposures create a plateau (continuous). Recurring exposures create irregular peaks (intermittent). Secondary spread creates progressively taller peaks separated by incubation periods (propagated).
Epidemic curves are graphical representations of these distinct outbreak dynamics.

Key Concept

Epidemic curve interpretation based on transmission dynamics
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Topics

Disease Surveillance and Outbreak Management

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