Communicable diseases: cryptosporidiosis in HIV: 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: cryptosporidiosis in HIV

Sample item

A man with advanced HIV infection has had profuse watery diarrhoea for 3 weeks. A stool smear stained by modified Ziehl-Neelsen shows small round acid-fast oocysts. The organism is also known to survive routine chlorination of water. Which pathogen is it?

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

The answer and the reasoning

C. Cryptosporidium parvum

Cryptosporidium causes self-limiting diarrhoea in the immunocompetent but chronic severe diarrhoea in advanced HIV infection. Its oocysts are acid-fast and resistant to ordinary chlorine concentrations, so filtration is needed for water treatment.

Option by option

  • A. Vibrio cholerae

    Vibrio cholerae is a bacterium killed by routine chlorination.

  • B. Entamoeba histolytica

    Entamoeba histolytica cysts are not acid-fast and the disease is typically dysenteric.

  • C. Cryptosporidium parvum (correct)

    Correct. Acid-fast oocysts and resistance to chlorination identify Cryptosporidium.

  • D. Balantidium coli

    Balantidium coli is a large ciliated protozoan seen on wet mount, not an acid-fast oocyst.

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 PSM questions

Questions about this PSM question

What is the answer to this PSM question?

The best answer is C, Cryptosporidium parvum. Cryptosporidium causes self-limiting diarrhoea in the immunocompetent but chronic severe diarrhoea in advanced HIV infection.

Why is "Vibrio cholerae" not the answer?

Vibrio cholerae is a bacterium killed by routine chlorination.

Why is "Entamoeba histolytica" not the answer?

Entamoeba histolytica cysts are not acid-fast and the disease is typically dysenteric.

Why is "Balantidium coli" not the answer?

Balantidium coli is a large ciliated protozoan seen on wet mount, not an acid-fast oocyst.

What concept does this question test?

It tests Communicable diseases: cryptosporidiosis in HIV in PSM. Its oocysts are acid-fast and resistant to ordinary chlorine concentrations, so filtration is needed for water treatment.

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: cryptosporidiosis in HIV?

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.