Legionella pneumophila is one of the important pathogens in community-acquired (CAP) and hospital-acquired pneumonia that can cause severe pneumonia. Early diagnosis and treatment of Legionella pneumonia (LP) are essential because inappropriate therapy for Legionella pneumonia has been reported to worsen the prognosis. The most frequently identified causative pathogen of Legionella pneumonia is Legionella pneumophila serogroup 1. Legionella pneumonia due to non-Legionella pneumophila serogroup 1 is seen in 20% of cases. In diagnosing Legionella pneumonia caused by non-Legionella pneumophila serogroup 1, the urinary antigen test is usually negative; therefore, we need to suspect Legionella pneumonia by clinical information such as symptoms, vital signs, laboratory findings, and radiological findings. Based on our previous report, Legionella pneumonia due to non-Legionella pneumophila serogroup 1 was a mild to severe pneumonia. In addition, in about half of the patients, we could not suspect Legionella pneumonia using a six-point scoring system, which is one of the diagnostic scoring systems. Recently, a new urinary antigen test kit that could theoretically diagnose Legionella pneumonia due to non-Legionella pneumophila serogroup 1 was released in Japan. This can help in early diagnosis of Legionella pneumonia, including the one caused by non-Legionella pneumophila serogroup 1.
Part of the book: Hospital Acquired Infection and Legionnaires' Disease