Communicable diseases: nocturnal periodicity in filariasis surveys: 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: nocturnal periodicity in filariasis surveys

Sample item

A survey team in a coastal district of India plans to collect thick blood films to detect microfilariae of Wuchereria bancrofti in residents. At what time should the blood be collected?

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

The answer and the reasoning

B. Between 10 pm and 2 am

Wuchereria bancrofti microfilariae in India show nocturnal periodicity, appearing in peripheral blood mainly at night with a peak around midnight. A night blood survey is therefore done between about 10 pm and 2 am to detect microfilaraemia.

Option by option

  • A. Between 6 am and 8 am

    Early morning is after the peak, when counts are falling and sensitivity is lower.

  • B. Between 10 pm and 2 am (correct)

    Correct. The microfilariae are in peripheral blood at night, with a peak close to midnight.

  • C. Between 12 noon and 2 pm

    Midday blood contains few or no microfilariae of the nocturnally periodic parasite.

  • D. Between 4 pm and 6 pm

    Late afternoon is before the microfilariae appear in the peripheral circulation.

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.

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Questions about this PSM question

What is the answer to this PSM question?

The best answer is B, Between 10 pm and 2 am. Wuchereria bancrofti microfilariae in India show nocturnal periodicity, appearing in peripheral blood mainly at night with a peak around midnight.

Why is "Between 6 am and 8 am" not the answer?

Early morning is after the peak, when counts are falling and sensitivity is lower.

Why is "Between 12 noon and 2 pm" not the answer?

Midday blood contains few or no microfilariae of the nocturnally periodic parasite.

Why is "Between 4 pm and 6 pm" not the answer?

Late afternoon is before the microfilariae appear in the peripheral circulation.

What concept does this question test?

It tests Communicable diseases: nocturnal periodicity in filariasis surveys in PSM. A night blood survey is therefore done between about 10 pm and 2 am to detect microfilaraemia.

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: nocturnal periodicity in filariasis surveys?

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.