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Difficulty: HardDisease Surveillance and Outbreak Management

A corporate medical director at a large manufacturing facility is investigating a cluster of employees who presented with high fever, cough, coryza, conjunctivitis, and a descending maculopapular rash. The initial cluster of three employees developed symptoms between April 2 and April 4. A subsequent cluster of five employees developed symptoms between April 14 and April 17. No other employees reported symptoms between April 5 and April 13. The suspected pathogen transmits via airborne respiratory particles and has a typical incubation period of 10 to 14 days. Several exposed coworkers, who are in their second trimester of pregnancy and lack immunity to the suspected pathogen, had documented close face-to-face contact with the second cluster of employees two days ago. They are currently asymptomatic. Which of the following represents the most accurate epidemiological classification of this outbreak pattern and the most appropriate immediate intervention for the pregnant coworkers?

  1. A
    Point source outbreak; administer the live-attenuated measles, mumps, and rubella vaccine to the exposed pregnant coworkers
  2. B
    Propagated outbreak; prescribe empiric broad-spectrum antibiotic prophylaxis to the exposed pregnant coworkers to prevent secondary pneumonia
  3. C
    Continuous common source outbreak; disclose the specific identities of the infected employees to the entire factory floor to ensure comprehensive contact tracing
  4. Propagated outbreak; administer pooled human immune globulin to the exposed pregnant coworkersAnswer
  5. E
    Propagated outbreak; initiate a case-control study by initially categorizing the remaining asymptomatic employees based on their exposure status to the ill workers

Answer

Propagated outbreak; administer pooled human immune globulin to the exposed pregnant coworkers
The outbreak demonstrates two distinct clusters of illness separated by approximately 10 to 13 days. Because this gap perfectly aligns with the pathogen's 10-14 day incubation period, the pattern strongly indicates secondary cases arising directly from contact with primary cases. This is the hallmark of a propagated (person-to-person) outbreak. Clinically, the combination of high fever, cough, coryza, conjunctivitis, and a descending maculopapular rash is highly specific for measles (rubeola). The exposed coworkers are pregnant and lack immunity. For susceptible pregnant women exposed to measles, the live-attenuated MMR vaccine is strictly contraindicated due to the theoretical risk of fetal infection. Instead, these high-risk contacts must receive pooled human immune globulin to provide immediate, safe passive immunity.

Step-by-Step Solution

1
Analyze the temporal distribution of cases relative to the incubation period.
The 10-13 day gap between the first cluster (April 2-4) and the second cluster (April 14-17) exactly matches the pathogen's 10-14 day incubation period.
Identifying the interval between peaks is essential to determine the mechanism of transmission in an outbreak.
2
Classify the outbreak pattern based on the epidemic curve data.
The outbreak is classified as a propagated (person-to-person) outbreak.
Successive peaks separated by one incubation period are the defining epidemiological hallmark of a propagated outbreak.
3
Identify the suspected pathogen based on the clinical presentation.
The classic presentation of cough, coryza, conjunctivitis, and a descending maculopapular rash indicates measles (rubeola).
Pathogen identification dictates the appropriate infection control and post-exposure prophylaxis protocols.
4
Determine the safest and most effective post-exposure prophylaxis for the specific exposed population (non-immune pregnant women).
Pooled human immune globulin is selected over the live-attenuated vaccine.
Live-attenuated vaccines are contraindicated in pregnancy due to theoretical fetal risks, making passive immunization with immune globulin the standard of care.

Key Concept

Epidemic curve interpretation of propagated outbreaks and appropriate post-exposure prophylaxis in contraindicated populations.
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Topics

Disease Surveillance and Outbreak Management

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