Hospital infection control: surveillance calculation: 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.

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Microbiology · Hospital infection control: surveillance calculation

Sample item

An ICU records 6 central line-associated bloodstream infections in a month during which central lines were in place for a total of 3,000 catheter-days. What is the CLABSI rate?

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

The answer and the reasoning

C. 2 per 1000 catheter-days

Device-associated infection rates use device-days as denominator, so they account for the time at risk: 6 divided by 3,000 catheter-days gives 0.002, and multiplying by 1,000 gives 2 per 1000 catheter-days. Using patient-days instead of device-days would distort comparisons between units with different line utilisation.

Option by option

  • A. 20 per 1000 catheter-days

    This multiplies by 10,000 and overstates the rate tenfold.

  • B. 0.2 per 1000 catheter-days

    This multiplies by 100 instead of 1000.

  • C. 2 per 1000 catheter-days (correct)

    Correct. 6 / 3000 x 1000 = 2 per 1000 catheter-days.

  • D. 500 per 1000 catheter-days

    This inverts the fraction: 3000 / 6 = 500 catheter-days per infection, which is not a rate per 1000 catheter-days.

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 C, 2 per 1000 catheter-days. Device-associated infection rates use device-days as denominator, so they account for the time at risk: 6 divided by 3,000 catheter-days gives 0.

Why is "20 per 1000 catheter-days" not the answer?

This multiplies by 10,000 and overstates the rate tenfold.

Why is "0.2 per 1000 catheter-days" not the answer?

This multiplies by 100 instead of 1000.

Why is "500 per 1000 catheter-days" not the answer?

This inverts the fraction: 3000 / 6 = 500 catheter-days per infection, which is not a rate per 1000 catheter-days.

What concept does this question test?

It tests Hospital infection control: surveillance calculation in Microbiology. 002, and multiplying by 1,000 gives 2 per 1000 catheter-days. Using patient-days instead of device-days would distort comparisons between units with different line utilisation.

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 Hospital infection control: surveillance calculation?

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.