Cross-reaction to Legionella pneumophila antigen in sera with elevated titers to Pseudomonas pseudomallei.

A significantly greater incidence (P less than 0.005) of Legionella pneumophila microagglutination titers greater than or equal to 32 was found in sera with elevated titers to Pseudomonas pseudomallei as compared with sera with negative titers for P. pseudomallei antibodies. The greater incidence of L. pneumophila titers in these sera suggests that L. pneumophila and P. pseudomallei share an antigen. The incidence of L. pneumophila microagglutination titers of greater than or equal to 32 in sera with elevated titers to Brucella abortus or Francisella tularensis is not statistically significant.