[Evaluation of the incidence of serological cross reactions between Legionella and Mycoplasma or Chlamydia].

Because of the possible serological cross reactions frequently described in the literature between L. pneumophila and M. pneumoniae or between L. pneumophila and Chlamydia, we decided to determine their frequency with our sera and our own methods. The anti M. pneumoniae and Chlamydia antibodies were researched in 162 sera samples from 46 cases of legionellosis serologically diagnosed and in 51 sera from 26 hyperimmunised rabbits. Conversely, anti L. pneumophila antibodies were researched in 165 sera from mycoplasmosis (61) or chlamydiosis (25 cases). None of the sera from mycoplasmosis or chlamydiosis tested by IFA and MA had antilegionella antibodies. None of the rabbits' sera hyperimmunised with Legionella had anti M. pneumoniae or Chlamydia antibodies. On the contrary, by complement fixation and IFA, out of the 46 cases of legionellosis under study, 6 showed a seroconversion in M. pneumoniae and 2 in Chlamydia. The Ig class determination did not show IgM titers in 7 of these 8 sera. The mechanisms of these cross reactions are discussed: antigens and methods used, booster effect during legionellosis, concurrent mycoplasmosis or chlamydiosis.