Increase in titers of antibodies to Mycoplasma pneumoniae in patients with purulent meningitis.

A fourfold or greater increase in titer of complement-fixing (CF) antibodies to Mycoplasma pneumoniae was found in 40.7% of paired sera from 54 patients with bacterial meningitis that had been proven by culture and in 10.3% of 39 patients with other bacteremic infections, but in none of eight patients with whooping cough or 40 patients with mumps meningitis. The CF antigen used was a crude lipid antigen, but comparable antibody increases were found by an enzyme-linked immunosorbent assay using a crude M. pneumoniae protein antigen. Increases were also frequently seen in nonspecific antibodies to the capsular polysaccharide of group A Neisseria meningitidis; these increases were significantly, but not completely, correlated to the nonspecific reactions to the mycoplasmal antigens. The data call for caution in interpreting serologic tests for M. pneumoniae when dealing with diseases not commonly associated with M. pneumoniae.