On investigating an outbreak, an epidemiologist plots an epidemic curve of acute febrile illness showing successive clusters separated by approximately 1 incubation period apart. Which of the following diseases shows this pattern of propagated spread?

1. A

   A. Measles

2. B

   B. Salmonellosis

3. C

   C. Typhoid

4. D

   D. Food poisoning

Appeared in: INI-CET EXAM -2026

Explanation

• The question describes a propagated epidemic curve, which has successive peaks of cases separated by one incubation period.
• This pattern is characteristic of diseases that spread directly from person to person.
• Measles is a highly contagious viral illness transmitted through respiratory droplets from an infected person to a susceptible person.
• Therefore, an outbreak of measles in a susceptible population would result in a propagated epidemic curve as the infection spreads from one individual to the next.

Why Other Options Were Wrong

• Option B: Salmonellosis is typically a foodborne illness resulting from a common-source exposure, such as consuming a contaminated food item. This leads to a point-source epidemic curve with a single, sharp peak, not successive waves.
• Option C: Typhoid fever is often spread through contaminated water or food (fecal-oral route). This usually results in a continuous common-source epidemic if the source (like a contaminated well) is not removed, leading to a plateau in the epidemic curve rather than distinct peaks.
• Option D: Food poisoning is the classic example of a point-source common-source epidemic. Exposure is brief and simultaneous for a group of people, causing a rapid, explosive rise and fall in cases within one incubation period. It does not show the person-to-person spread pattern of a propagated epidemic.

Related Visual

Clinical Relevance

• Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Epidemiological curves and patterns of disease spread as background academic context rather than a clinical decision trigger.
• For a community health nurse, identifying the type of epidemic curve is crucial for implementing the correct public health interventions.
• A propagated curve (like for measles) indicates person-to-person spread, necessitating measures like isolation, quarantine, contact tracing, and vaccination campaigns to break the chain of transmission.
• A common-source curve (like for food poisoning) points to a contaminated source (e.g., food, water), requiring investigation to identify and remove the source to prevent further cases.

How to Approach the Question

• First, analyze the description of the epidemic curve provided in the question: 'successive clusters separated by approximately 1 incubation period apart'.
• Recognize this description as the hallmark of a 'propagated' or 'progressive' epidemic.
• Understand that a propagated epidemic is caused by the transmission of an infectious agent from one person to another.
• Review the options and determine the primary mode of transmission for each disease.
• Measles is spread person-to-person. Salmonellosis, Typhoid, and Food Poisoning are typically spread through a common source (food or water).
• Select the disease that matches the person-to-person transmission model required for a propagated epidemic.

Concept Tested & Keywords

• Concept Tested: Epidemiological curves and patterns of disease spread
• Stem keywords: epidemic curve, successive clusters, 1 incubation period apart, propagated spread
• Lead-in keywords: shows this pattern
• Negative lead-in flag: false

Question ID

Qlc7SU-AgM6KjpctKBv6kE

Copy ID

Reference Book

E6 Parks TextBook of Preventive & Social Medicine part 1 — Subpart A (pp 26-201 of 604) pp. 57-59, 58-60