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Internal Medicine

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A 65-year-old man is seen for pneumonia. He has had a non-productive cough, fever, headache, and anorexia for five days.

He says two friends currently are hospitalized for pneumonia at another institution. The last time he saw his hospitalized friends was three weeks ago when they gathered with two other friends to have dinner at a friend’s rural home. Now three of 6 individuals at that gathering have acute, febrile pneumonias.

He remembers the evening well because the family cat gave birth to a litter in the same room during the dinner.

  • T 102.2°F; P 70; BP128/88; RR 28.

  • Chest clear.

  • WBC 6,200 with normal differential.

  • Platelet count 55,000

  • AST and ALT 3x normal

  • X-ray = infiltrate right lower lobe.

Which one of the following is the most likely cause of pneumonia in the three friends?

  • Streptococcus pneumoniae

  • Legionella

  • Coxiella

  • Listeria

Mazen Kherallah

The incubation period for Q Fever (Coxiella burnettii) is usually 14-22 days (range 9-39 days) while Legionella is shorter (2-10 days). Listeria and Brucella don’t cause pneumonia typically, so they don’t fit although Brucella has an incubation period similar to Q fever. The cluster and incubation period do not fit pneumococcal disease.

Humans acquire Q Fever pneumonia due to Coxiella burnetii by inhaling infected aerosols from animals, particularly cattle, goats and sheep, but also cats, dogs, and rabbits. In infected animals, high concentrations of Coxiella are found in the placenta, so aerosols at the time of parturition are often the source of human infection. The incubation period is about 3 weeks. Simultaneous pneumonia and hepatitis should always raise the possibility of Q fever. Thrombocytopenia and a temperature-pulse disparity are common.

The above scenario is based on a well-known outbreak published many years ago that question writers might remember!

Common source outbreaks of pneumococcal pneumonia are rare and usually seen with severe crowding as in jail settings.

Legionella can cause pneumonia, hepatitis, and a temperature-pulse disparity, but the incubation period here is too long and most patients with Legionnaire’s have leukocytosis.


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