Legionnaires' disease at a Dutch flower show: prognostic factors and impact of therapy - Research

Emerging Infectious Diseases, Dec, 2002 by Kamilla D. Lettinga, Annelies Verbon, Gerrit-Jan Weverling, Joop F.P. Schellekens, Jeroen W. Den Boer, Ed P.F. Yzerman, Jacobus Prins, Wim G. Boersma, Ruud J. van Ketel, Jan M. Prins, Peter Speelman

Identification of patients with Legionnaires' disease has important implications for the choice of initial therapy. Studies comparing the clinical manifestations of Legionella pneumonia to other types of pneumonia have indicated that Legionnaires' disease is not "atypical" and that individual clinical features such as diarrhea, confusion, hyponatremia, and chest x-ray findings are not sufficiently distinctive to distinguish Legionnaires' disease from other types of community-acquired pneumonia (18,24-26). The results of cultures require several days, and serum antibody tests have a low sensitivity. In patients with Legionnaires' disease related to this outbreak, sensitivity was approximately 43% for one of the three separate antibody tests and 61% for any of the tests, using a positive culture result, a urinary antigen test with positive results, or both as the criterion standard (E. Yzerman, pers. comm.).

Detection of L. pneumophila antigens in a urine sample provides a diagnosis within 1 hour, with a specificity of 95% to 100% (11) (Binax Now Legionella urinary antigen test, Binax). Patients in our study with a positive urine test during hospitalization had an increased risk for ICU admission or death, in accordance with data indicating that the percentage of positive test results increased with the clinical severity of the disease (27). Although the urinary antigen test was done retrospectively in many patients (median 9 days after the first symptoms, range 0-25 days), the number of positive urinary tests is not lower during the first 3 days after symptoms than after 3 weeks of illness (28). The urinary antigen test used during this outbreak detects L. pneumophila serogroup 1, which is responsible for approximately 70%-80% of Legionnaires' disease cases in the United States and Europe.

Increased deaths associated with delay of adequate treatment for Legionnaires' disease has been reported earlier (1,5); in patients suspected of having Legionnaires' disease, adequate therapy should therefore be started as soon as possible. To ensure coverage of potential

L. pneumophila infections in every patient, the recommendations for treatment of patients with community-acquired pneumonia have been expanded. The new guidelines from the Infectious Diseases Society of America recommend an extended-spectrum cephalosporin plus a macrolide or a fluoroquinolone alone, for every hospitalized patient in whom no pathogen is defined (6). This approach may lead to overtreatment since 2%-13% of community-acquired pneumonia is caused by L. pneumophila (18,29,30). Therefore, this approach is costly and, in addition, may contribute to macrolide and fluoroquinolone resistance.

The results of our study suggest that a more tailored approach of patients with community-acquired pneumonia may be possible. When Legionnaires' disease is considered in the differential diagnosis of patients with community-acquired pneumonia, a urinary antigen test should be done on admission. If test results are positive, the patient should be treated immediately with a fluoroquinolone or a macrolide since a positive urinary test on admission identifies the patients with Legionnaires' disease caused by L. pneurnophila serogroup 1 and a high risk for ICU admission or death. If the urinary antigen test gives negative results, deferring anti-Legionella therapy for the first 24 hours after admission, pending the diagnostic work-up, may be justified because the outcome in Legionnaires' disease is not influenced. In this way, unnecessary use of antibiotics in patients hospitalized with community-acquired pneumonia may be avoided.