What are the key clinical features that suggest a diagnosis of Legionnaires' disease in a patient presenting with pneumonia?

Key clinical features suggesting Legionnaires' disease in a patient with pneumonia include:

• A severe pneumonia presentation often accompanied by systemic symptoms such as high fever, chills, and malaise ¹.
• Relative bradycardia (a pulse-temperature dissociation where the heart rate is lower than expected for the degree of fever) is a distinctive clinical clue ¹[(Cunha, 2010)].
• Gastrointestinal symptoms such as diarrhoea, nausea, vomiting, and abdominal pain are more common in Legionnaires' disease compared to other pneumonias ¹[(Fairbank et al., 1991); (Cunha, 2010)].
• Neurological symptoms including headache, confusion, or other cognitive changes may be present, reflecting systemic involvement ¹[(Meyer and Finegold, 1980); (Cunha, 2010)].
• Hyponatraemia (low sodium levels) and elevated liver enzymes are common laboratory abnormalities that support the diagnosis ¹[(Cunha, 2010)].
• Chest X-ray findings may show patchy unilobar infiltrates that can progress rapidly, sometimes with pleural effusion ¹.
• Exposure history such as recent travel, stay in hotels, or contact with contaminated water sources (e.g., air conditioning systems) should raise suspicion ¹.

These features collectively help differentiate Legionnaires' disease from typical bacterial pneumonias and other atypical pneumonias, guiding appropriate diagnostic testing and management ¹[(Cunha, 2010)].