A case report of legionaire's disease in an immunocompromised patient

Legionella pneumophila is one of the most important pathogens that can cause severe community-acquired pneumonia. It may present as Pontiac fever, a mild and self-limiting disease, or Legionnaire's disease, which usually causes severe pneumonia with high mortality. Although there are several unique features of Legionnaire's disease, it remains a challenge to differentiate Legionnaire's disease from influenza pneumonia due to the clinical and radiological similarities or overlapping between these two diseases. However, early initiation of appropriate therapy reduces mortality. Here, we present the case of a 48-year-old female patient, who had systemic lupus erythematous and underwent long-term steroid treatment. She presented with severe community-acquired pneumonia during the influenza season. Influenza pneumonia was suspected initially according to her travel history and clinical presentation, but Legionnaire's disease was confirmed according to urine antigen assay and sputum culture. The patient died of multiple organ failure in three weeks despite aggressive antibiotic treatment. This article reviewed the clinical features of legionellosis in both immunocompetent and immunocompromised hosts, and compared the difference in clinical presentation between legionellosis and influenza infection.