Bacteriology: Coxiella burnetii: 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 · Bacteriology: Coxiella burnetii

Sample item

A 45-year-old shepherd has fever for six weeks and a new aortic regurgitation murmur. Several blood cultures on routine media are negative and the Weil-Felix test is negative. Serology shows a very high phase I IgG titre. Which organism and conclusion fit best?

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

The answer and the reasoning

A. Coxiella burnetii, with a high phase I titre indicating chronic infection such as endocarditis

Q fever is caused by Coxiella burnetii and is acquired by inhaling aerosols from infected sheep, goats or cattle. It is a cause of culture-negative endocarditis, and a high phase I IgG titre indicates chronic disease, whereas acute infection shows rising phase II antibody. It is the rickettsia-like organism for which Weil-Felix is negative. Doxycycline with hydroxychloroquine is used for endocarditis.

Option by option

  • A. Coxiella burnetii, with a high phase I titre indicating chronic infection such as endocarditis (correct)

    Phase I IgG elevation after animal exposure with culture-negative endocarditis indicates chronic Q fever.

  • B. Bartonella quintana, spread by body lice and shown by Weil-Felix OX-K

    Bartonella quintana is louse-borne and not associated with sheep, and OX-K does not detect it.

  • C. Brucella melitensis, with a high phase I titre indicating acute infection

    Brucella can be cultured from blood and is detected by agglutination, and it lacks a phase I antigen.

  • D. Orientia tsutsugamushi, spread by trombiculid mites

    Orientia causes scrub typhus with an eschar and OX-K positivity, not endocarditis with phase I antibody.

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 Microbiology question

What is the answer to this Microbiology question?

The best answer is A, Coxiella burnetii, with a high phase I titre indicating chronic infection such as endocarditis. Q fever is caused by Coxiella burnetii and is acquired by inhaling aerosols from infected sheep, goats or cattle.

Why is "Bartonella quintana, spread by body lice and shown by Weil-Felix OX-K" not the answer?

Bartonella quintana is louse-borne and not associated with sheep, and OX-K does not detect it.

Why is "Brucella melitensis, with a high phase I titre indicating acute infec…" not the answer?

Brucella can be cultured from blood and is detected by agglutination, and it lacks a phase I antigen.

Why is "Orientia tsutsugamushi, spread by trombiculid mites" not the answer?

Orientia causes scrub typhus with an eschar and OX-K positivity, not endocarditis with phase I antibody.

What concept does this question test?

It tests Bacteriology: Coxiella burnetii in Microbiology. It is a cause of culture-negative endocarditis, and a high phase I IgG titre indicates chronic disease, whereas acute infection shows rising phase II antibody. It is the rickettsia-like organism for which Weil-Felix is negative. Doxycycline with hydroxychloroquine is used for endocarditis.

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 Bacteriology: Coxiella burnetii?

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.