[Problems in the serological diagnosis of atypical pneumonia caused by Legionella pneumophila and Mycoplasma pneumoniae].

Introduction: The clinical presentation of atypical pneumonia is often similar to the presentation of more typical bacterial pneumonias and the etiological agent must be confirmed by laboratory diagnosis. This article will discuss the problems in the serological diagnosis of atypical pneumonia caused by Legionella pneumophila and Mycoplasma pneumoniae which are the agents most commonly associated with atypical pneumonia. Specifically, seeking the possibility of non-specific response, we evaluated the prevalence of antibodies to M. pneumoniae in serum samples obtained from patients suspected in clinical investigation for legionellosis.

Methods: The total numbers of 261 serum obtained from patients suspected in clinical investigation for legionellosis, were tested by in-house ELISA with M. pneumoniae sonicated antigen. Some of the positive sera were also re-tested by western-blot with high specific recombinant M. pneumoniae P1 protein.

Results: The diagnostic significant level of IgA antibodies to M. pneumoniae were diagnosed by ELISA in 71 (27,2%) of tested serum samples. Some of the IgA-positive sera have also high level of IgG and IgM antibodies to M pneumoniae (respectively 4,2% and 6,5%). Most from the 18 selected positive results obtained by ELISA were also confirmed by western-blot. It was characteristic that IgA antibodies to M pneumoniae were detected more than three times often in serum samples with positive serological tests for Legionnaires' disease than in samples with negative results for L. pneumophila.

Conclusions: This study showed the possibility of non-specific reactions in serological diagnosis of atypical pneumonia. However, according to the data of the literature, co-infections of L. pneumophila and M pneumoniae can not be excluded.