Which pneumonia typically peaks in late summer and presents with high fever, toxic appearance, bradycardia, and diarrhea?

• A. Chlamydia pneumonia
• B. Legionnaires
• C. Pneumococcal pneumonia
• D. Mycoplasma

Answer: (B)

Legionella pneumonia (Legionnaires disease) is tested by recognizing a distinctive cluster of features: it often peaks in late summer when aerosolized water sources, such as air conditioning systems and decorative fountains, become culprits. Patients tend to look seriously ill with a high fever and a toxic appearance, and they frequently have gastrointestinal symptoms like diarrhea. A classic clue is relative bradycardia—the heart rate is not as fast as you’d expect for a high fever. Together, these signs point toward Legionella more than other common pneumonias.

Other pneumonias don’t usually present with this exact combination. Chlamydia pneumonia tends to be milder and more gradual, without the pronounced GI symptoms or bradycardia. Mycoplasma is typical in younger adults with a milder course and often a dry cough, sometimes bullous myringitis, rather than the severe systemic toxicity. Pneumococcal pneumonia classically presents with abrupt onset of high fever, a productive rusty sputum, and focal lobar consolidation, not the GI symptoms and relative bradycardia that point to Legionella.

Knowing these features helps distinguish Legionella from other causes and guides appropriate diagnostic testing, such as the urinary antigen test for Legionella pneumophila serogroup 1, and targeted therapy with a macrolide or fluoroquinolone.