Clinical microbiology and hospital infection control: Clostridioides difficile testing algorithm: practice question

A Microbiology 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.

Try it

Microbiology · Clinical microbiology and hospital infection control: Clostridioides difficile testing algorithm

Sample item

A hospitalised patient on clindamycin has five loose stools a day. Stool glutamate dehydrogenase antigen is positive, but the toxin enzyme immunoassay is negative. What is the next step?

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

The answer and the reasoning

D. Nucleic acid amplification test for the toxin gene

GDH detects the organism but not toxin production, while toxin EIA is less sensitive. In the two-step algorithm, discordant GDH-positive, toxin-negative results are arbitrated by PCR for the toxin gene to detect toxigenic strains.

Option by option

  • A. Repeat the toxin immunoassay on the same sample

    Repeating the same insensitive assay on the same sample adds nothing.

  • B. Report that the infection is excluded

    A positive GDH with symptoms means infection cannot be excluded on the toxin EIA alone.

  • C. Send stool for ova and cysts

    Ova and cysts do not explain antibiotic-associated diarrhoea.

  • D. Nucleic acid amplification test for the toxin gene (correct)

    Correct. PCR for the toxin gene arbitrates a discordant GDH and toxin result.

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.

More Microbiology questions

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is D, Nucleic acid amplification test for the toxin gene. GDH detects the organism but not toxin production, while toxin EIA is less sensitive.

Why is "Repeat the toxin immunoassay on the same sample" not the answer?

Repeating the same insensitive assay on the same sample adds nothing.

Why is "Report that the infection is excluded" not the answer?

A positive GDH with symptoms means infection cannot be excluded on the toxin EIA alone.

Why is "Send stool for ova and cysts" not the answer?

Ova and cysts do not explain antibiotic-associated diarrhoea.

What concept does this question test?

It tests Clinical microbiology and hospital infection control: Clostridioides difficile testing algorithm in Microbiology. In the two-step algorithm, discordant GDH-positive, toxin-negative results are arbitrated by PCR for the toxin gene to detect toxigenic strains.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Clinical microbiology and hospital infection control: Clostridioides difficile testing algorithm?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology 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.