[Francisella tularensis: update on microbiological diagnosis after an epidemic outbreak]

Francisella tularensis is a facultative intracellular gramnegative aerobic coccobacilli which is difficult to isolate. The appearance of an epidemic outbreak of tularemia in Castilla y Leon (Spain) during the first months of 1998 led bur microbiology laboratory to develop the diagnostic methods of this disease which, up to then, were unknown by the authors.

During the months of January and February, 1998, 25 samples were processed for culture (17, adenopathy pus and 8 necrotic skin ulcers) using enriched culture mediums. In 20, direct immunofluorescence was performed on the sample spread. Serologic study was carried out in 352 patients by the agglutination technique in tubes, with titers > or = 1/160 being considered as positive. Susceptibility tests were performed by the disk plate technique in chocolate agar.

Three isolates of F. tularensis were achieved (12%). Seven samples (38.8%) were positive by direct immunofluorescence. By serology 149 negative (42%) and 203 positive (58%) results were obtained. Seroconversion was observed in 53 patients (increase in titer value 4-fold above the basal determination). The strains isolated were sensitive to third generation cephalosporins, aminoglycosides, macrolides and quinolones.

F. tularensis is a microorganism which is highly demanding of its culture. Serology and direct immunofluorescence are more effective techniques for the diagnosis of tularemia than cultures. The strains presented high sensitivity to the antibiotics tested. Since the appearance of this outbreak, tularemia should be included in the differential diagnosis of the infectious processes observed in Spain.