Communicable diseases: measles communicability: practice question

A PSM question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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PSM · Communicable diseases: measles communicability

Sample item

A 6-year-old boy attending a primary school develops a maculopapular rash that began behind the ears and spread downwards. The class teacher asks for how long he should stay away from school to protect classmates. Which period best describes the communicability of measles?

AFrom 7 days before the rash until desquamation is completeBOnly during the prodromal phase, before the rash appearsCFrom about 4 days before to 4 to 5 days after the onset of the rashDFrom the onset of rash until 3 weeks later

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. From about 4 days before to 4 to 5 days after the onset of the rash

Measles is most infectious in the prodromal (catarrhal) phase and remains communicable until about 4 to 5 days after the rash appears. Isolation of the patient for this period limits spread in schools. Because infectivity starts before the rash, many contacts are exposed before the diagnosis is made.

Option by option

A. From 7 days before the rash until desquamation is complete
Desquamation is not required for the end of infectivity; the communicable period ends about 4 to 5 days after the rash.
B. Only during the prodromal phase, before the rash appears
Infectivity does not end when the rash appears; it continues for about 4 to 5 days afterwards.
C. From about 4 days before to 4 to 5 days after the onset of the rash (correct)
Correct. Communicability spans roughly 4 days before to 4 to 5 days after rash onset.
D. From the onset of rash until 3 weeks later
A 3-week period is far too long; this is closer to the shedding pattern of some other infections, not measles.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this PSM question

What is the answer to this PSM question?

The best answer is C, From about 4 days before to 4 to 5 days after the onset of the rash. Measles is most infectious in the prodromal (catarrhal) phase and remains communicable until about 4 to 5 days after the rash appears.

Why is "From 7 days before the rash until desquamation is complete" not the answer?

Desquamation is not required for the end of infectivity; the communicable period ends about 4 to 5 days after the rash.

Why is "Only during the prodromal phase, before the rash appears" not the answer?

Infectivity does not end when the rash appears; it continues for about 4 to 5 days afterwards.

Why is "From the onset of rash until 3 weeks later" not the answer?

A 3-week period is far too long; this is closer to the shedding pattern of some other infections, not measles.

What concept does this question test?

It tests Communicable diseases: measles communicability in PSM. Isolation of the patient for this period limits spread in schools. Because infectivity starts before the rash, many contacts are exposed before the diagnosis is made.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Communicable diseases: measles communicability?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.