An outbreak of Legionnaires' disease associated with a circulating bathwater system at a public bathhouse. I: a clinical analysis

Few reports have analyzed the clinical manifestations of patients with Legionnaires' disease in large outbreaks throughout the world. We retrospectively evaluated the clinical presentation and prognostic factors in 76 patients with Legionnaires' disease, reported by local physicians, in a large outbreak resulting from contamination of the water in a public bathhouse in Miyazaki, Japan. Fever, gastrointestinal tract symptoms, and abnormal neurological findings were seen in 95%, 35%, and 21% of the 76 patients, respectively. Respiratory tract symptoms were seen in only 42% of the patients, although all of these patients revealed pneumonia on chest X-ray. Only 20 (31%) of the 64 patients who had microbiological tests were reported to have positive results for one of the three microbiological tests (sputum culture, serology, and urinary antigen) which are specific for Legionella infection. Based on univariate analysis, the existence of neurological symptoms, elevated levels of C-reactive protein and transaminases, hyponatremia, a positive urinary antigen test, and serological evidence of Legionella infection were independent risk factors for poor clinical courses in patients with Legionnaires' disease. Patients treated with antimicrobial agents, such as macrolides, tetracyclines, and/or fluoroquinolones, within 3 days of onset of illness exhibited significantly better outcomes, when assessed by a multivariate logistic-regression model, after adjusting for the severity of pneumonia. Taking a careful history and documenting potential Legionella exposure, as well as microbiological testing, is important for an accurate diagnosis of Legionnaires' disease. Antimicrobials effective against Legionella bacteria should be administered without delay in subjects with suspected Legionnaires' disease.