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Colonization of the respiratory tract with Legionella species
R Finkelstein1, W A Palutke, B B Wentworth
1Division of Infectious Diseases, Wayne State University School of Medicine, Detroit, Michigan.
Abstract:
Pneumonia is the most important manifestation of disease caused by Legionella species. However, it is still not known for certain how these organisms actually enter the lungs. During a 5-month period 318 hospitalized patients without clinical or radiologic features of pneumonia were enrolled in a survey of sputum colonization with Legionella. Diagnostic tests included cultures, direct fluorescent antibody test (DFA) and DNA probe assay of sputum. Colonization was considered to occur when at least one of these tests was positive. According to our definitions, 1.2-10% of of these patients could have been colonized by Legionella spp. However, all cultures were negative and in all but one of these patients the DFA was the only positive test. A case-control study comparing test-positive and test-negative patients failed to identify any different features of disease or epidemiologic characteristics. These findings suggest that a high rate of false-positive DFA results occurred in our study rather than any new evidence of colonization of the respiratory tract with Legionella.
Insights
This study investigated Legionella colonization in hospitalized patients. Findings suggest the direct fluorescent antibody test (DFA) may produce false-positive results, rather than indicating true respiratory tract colonization.
Area of Science:
- Microbiology
- Infectious Diseases
- Pulmonary Medicine
Background:
- Legionella species are a significant cause of pneumonia.
- The mechanism of Legionella entry into the lungs remains unclear.
- Understanding respiratory tract colonization is crucial for diagnosing Legionella infections.
Purpose of the Study:
- To investigate the prevalence and diagnostic methods of Legionella sputum colonization in hospitalized patients without pneumonia.
- To evaluate the reliability of diagnostic tests, including cultures, direct fluorescent antibody (DFA), and DNA probe assays.
- To determine if colonization indicates a risk for developing Legionella pneumonia.
Main Methods:
- A 5-month survey enrolled 318 hospitalized patients without clinical or radiologic pneumonia.
- Sputum samples were analyzed using cultures, DFA, and DNA probe assays.
- A case-control study compared patients with positive and negative test results.
Main Results:
- 1.2-10% of patients could have been colonized based on initial definitions.
- All cultures were negative; DFA was the only positive test in most cases.
- No significant differences in disease features or epidemiology were found between test-positive and test-negative groups.
Conclusions:
- The study suggests a high rate of false-positive results from the DFA test for Legionella.
- The findings do not provide new evidence for respiratory tract colonization with Legionella in this patient group.
- Re-evaluation of diagnostic methods is needed to accurately detect Legionella colonization.