Communicable diseases: Legionnaires disease source: 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: Legionnaires disease source

Sample item

Several guests of a hotel with a central air-conditioning system develop high fever, confusion, diarrhoea and pneumonia with low serum sodium. There is no spread from patients to their carers. What is the most likely mode of transmission?

ADirect contact with contaminated fomitesBFaecal-oral spread through contaminated foodCInhalation of aerosols from contaminated cooling tower waterDDroplet spread from coughing patients

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

The answer and the reasoning

C. Inhalation of aerosols from contaminated cooling tower water

Legionella pneumophila grows in warm water systems such as cooling towers, hot water tanks and showers, and infects when contaminated aerosols are inhaled. Person-to-person spread does not occur, so control focuses on maintaining and disinfecting water systems.

Option by option

A. Direct contact with contaminated fomites
Fomite spread is not the recognised route for this pneumonia.
B. Faecal-oral spread through contaminated food
The gastrointestinal symptoms here are a feature of the illness and do not indicate a faecal-oral route.
C. Inhalation of aerosols from contaminated cooling tower water (correct)
Correct. Aerosols from contaminated water systems are the usual source, with no person-to-person spread.
D. Droplet spread from coughing patients
Droplet spread from patients does not occur in this infection.

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, Inhalation of aerosols from contaminated cooling tower water. Legionella pneumophila grows in warm water systems such as cooling towers, hot water tanks and showers, and infects when contaminated aerosols are inhaled.

Why is "Direct contact with contaminated fomites" not the answer?

Fomite spread is not the recognised route for this pneumonia.

Why is "Faecal-oral spread through contaminated food" not the answer?

The gastrointestinal symptoms here are a feature of the illness and do not indicate a faecal-oral route.

Why is "Droplet spread from coughing patients" not the answer?

Droplet spread from patients does not occur in this infection.

What concept does this question test?

It tests Communicable diseases: Legionnaires disease source in PSM. Person-to-person spread does not occur, so control focuses on maintaining and disinfecting water systems.

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: Legionnaires disease source?

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.