Communicable diseases: bacteriological index in leprosy: 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: bacteriological index in leprosy

Sample item

A slit-skin smear from a patient with leprosy shows 10 to 100 acid-fast bacilli in an average oil-immersion field. What bacteriological index is recorded on Ridley's logarithmic scale?

A3+B2+C4+D5+

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

The answer and the reasoning

C. 4+

On Ridley's logarithmic scale the bacteriological index runs from 0 to 6+: 1+ is 1 to 10 bacilli per 100 fields, 2+ is 1 to 10 per 10 fields, 3+ is 1 to 10 per field, 4+ is 10 to 100 per field, 5+ is 100 to 1000 per field and 6+ is over 1000 per field.

Option by option

A. 3+
A grade of 3+ corresponds to 1 to 10 bacilli per field.
B. 2+
A grade of 2+ corresponds to 1 to 10 bacilli per 10 fields.
C. 4+ (correct)
Correct. Ten to 100 bacilli per average field is graded 4+.
D. 5+
A grade of 5+ corresponds to 100 to 1000 bacilli per field.

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, 4+. On Ridley's logarithmic scale the bacteriological index runs from 0 to 6+: 1+ is 1 to 10 bacilli per 100 fields, 2+ is 1 to 10 per 10 fields, 3+ is 1 to 10 per field, 4+ is 10 to 100 per field, 5+ is 100 to 1000 per field and 6+ is over 1000 per field.

Why is "3+" not the answer?

A grade of 3+ corresponds to 1 to 10 bacilli per field.

Why is "2+" not the answer?

A grade of 2+ corresponds to 1 to 10 bacilli per 10 fields.

Why is "5+" not the answer?

A grade of 5+ corresponds to 100 to 1000 bacilli per field.

What concept does this question test?

It tests Communicable diseases: bacteriological index in leprosy in PSM. The correct option holds because: Correct. Ten to 100 bacilli per average field is graded 4+.

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: bacteriological index in leprosy?

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.