Cross-reactions in IgM ELISA tests to Legionella pneumophila sg1 and Bordetella pertussis among children suspected of legionellosis; Potential impact of vaccination against pertussis?

Abstract

The objective of this study was preliminary evaluation of IgM cross-reaction in sera collected from children hospitalized because of suspected legionellosis. Sera with positive IgM results to L. Pneumophila sgs1-7, B. Pertussis or with simultaneous detection of IgM antibodies to L. Pneumophila sgs1-7 and B. Pertussis, or IgM to L. Pneumophila sgs1-7 and M. Pneumoniae in routine tests, were selected. In total, an adapted pre-absorption test was used for the serological confirmation of legionellosis in the sera of 19 children suspected of legionellosis, and also in 3 adult persons with confirmed Legionnaires¡¯ disease. Sera were pre-absorbed with antigens of L. Pneumophila sg1, B. Pertussis or both, and tested by ELISA tests. The reduction of IgM antibody level by pre-absorption with antigen/antigens was determined. Reduction of anti-Lpsgs1-7 IgM by pre-absorption with L.pneumophila sg1 antigen ranged from 1.5 to 80, and reduction of anti-Bp IgM by pre-absorption with B. Pertussis ranged from 2.0 to 23.8. Reduction by both antigens varied depending on the age of the patients: among children <4 yrs.old, the reduction of anti-B. Pertussis IgM by both antigens was higher than for B. Pertussis antigen alone. Based on the high difference (≥ 2 times) between reduction by L.pneumophila sg1 and by B. Pertussis antigen, legionellosis was confirmed in 8/19 children. The majority of them also indicated IgM positive/borderline results for B. Pertussis or M.pneumoniae in routine ELISA tests. As a preliminary, we posed a hypothesis of a potential impact of an anti-pertussis vaccination on the results obtained in anti-L. Pneumophila ELISA IgM tests among young children.