Legionella pneumophila cases in a community hospital: A 12-month retrospective review

BACKGROUND: Legionella pneumonia has long been recognized as an important cause of community-acquired pneumonia associated with significant morbidity and mortality; however, the description of the incidence of this disease is restricted to sporadic cases in the literature. With the advent of an inexpensive and rapid urine antigen test, routine testing has become more common. We report findings of a retrospective review of 266 patients who were admitted with a clinical diagnosis of community-acquired pneumonia over a 12-month period and were tested for Legionella pneumophila serogroup 1, reporting the prevalence and determinants of Legionella infection. METHODS: Chart reviews of 266 patients admitted for community-acquired pneumonia and who underwent urine antigen testing for Legionella pneumophila during a 1-year time period were conducted, looking at demographic information as well as clinical and laboratory presentation, reporting on the prevalence and determinants of urine antigen positivity using multivariate logistic regression analysis. RESULTS: Legionella pneumophila serogroup 1 was found in 2.3% of cases of community-acquired pneumonia. We also found that altered mental status, diarrhea, history of lung disease, and alcohol intake were significantly associated with pneumonia associated with Legionella. The presence of these four factors had a low sensitivity in predicting Legionella infection (33%); however, they had a positive predictive value of 98%, with a specificity of 100. All the Legionella-infected patients in our study required admission to the intensive care unit, and one of them developed Guillain–Barré syndrome, which to our knowledge represents the only reported case of this syndrome related to Legionella infection in an adult in the English scientific literature. CONCLUSION: Legionella pneumophila serogroup 1 is a common cause of sporadic cases of community-acquired pneumonia associated with a high morbidity and protean manifestations. Clinical features have a poor sensitivity in identifying cases, and routine urine antigen testing in patients with suggestive clinical symptoms appears to be a rational approach in the evaluation of community-acquired pneumonia.