FALSE-POSITIVE LEGIONELLA TITERS IN ROUTINE CLINICAL SEROLOGY TESTINGDETECTED BY ABSORPTION WITH CAMPYLOBACTER - IMPLICATIONS FOR THE SEROLOGICAL DIAGNOSIS OF LEGIONNAIRES-DISEASE

A simple absorption step using blocking fluid prepared from a selected campylobacter strain was introduced in parallel with routine legionel la serology tests. Over 12 months, 2716 patients were tested for legio nella antibodies by the Indirect Fluorescent Antibody Test of whom 58 (2.1%) had a positive titre (greater than or equal to 16) in one or mo re sera. Campylobacter blocking fluid significantly reduced the legion ella titres in 17 of these patients (29%) including four patients with diagnostic serology results (two of whom had pneumonia) and 13 patien ts with non-diagnostic titres. Absorption with campylobacter however h ad no effect on the legionella titres in 10 patients with positive ser ology, in whom legionnaires' disease had been confirmed by culture of Legionella pneumophila from sputum or detection of legionella urinary antigen by ELISA. These results indicate that the serological cross-re action between legionella and campylobacter is encountered in routine legionella serology tests. The important implications for the diagnosi s of legionnaires' disease are discussed.