[The role of the clinical microbiology laboratory during the outbreak of Legionella spp. in the municipality of Alcoy: the effectiveness of the different diagnosis methods].

BACKGROUND

The effectiveness of the different laboratory test methods to diagnose Legionella spp. in clinical specimens varies according to the epidemiological context. In this study, the usefulness of the laboratory methods used for an outbreak that occurred in the municipality of Alcoy (Alicante, Spain) are evaluated.

MATERIALS AND

METHODS

222 community-acquired cases of infection caused by Legionella pneumophila serogroup 1, subtype Pontiac-Knoxville, genotypes I and II were studied, that had been diagnosed by the Microbiology laboratory from January 1999 to December 2000, corresponding to patients residing in the municipality of Alcoy (Alicante). The methods used were direct antigen detection in respiratory specimens by immunoflurescence, direct antigen detection in urine, cultures and serology.

RESULTS

The detection of the antigen in urine diagnosed 201 cases (90,5%). Direct immunofluorescence provided a high number of false positives (n=24). A culture was essential to confirm the etiology of the outbreak (25 sputum) strains from 22 patients). Serology complemented the other methods and helped to retrospectively diagnose 21 patients (9%) when the other tests were not carried out or when they provided negative results.

CONCLUSIONS

A rapid diagnosis is essential to evaluate the patients and to control epidemical outbreaks, and the detection of the urinary antigen is very useful, but should be complemented with other methods. The culture of the respiratory specimens and the subsequent typing of the strains means that the etiology can be established with certainty and this helps to determine the source(s) of the infection. Serology complemented the diagnosis in 9% of the cases.